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Molecular characterization of the gastrula in the turtle Emys orbicularis: an evolutionary perspective on gastrulation. PLoS One 2008; 3:e2676. [PMID: 18628985 PMCID: PMC2442194 DOI: 10.1371/journal.pone.0002676] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2008] [Accepted: 05/23/2008] [Indexed: 11/19/2022] Open
Abstract
Due to the presence of a blastopore as in amphibians, the turtle has been suggested to exemplify a transition form from an amphibian- to an avian-type gastrulation pattern. In order to test this hypothesis and gain insight into the emergence of the unique characteristics of amniotes during gastrulation, we have performed the first molecular characterization of the gastrula in a reptile, the turtle Emys orbicularis. The study of Brachyury, Lim1, Otx2 and Otx5 expression patterns points to a highly conserved dynamic of expression with amniote model organisms and makes it possible to identify the site of mesoderm internalization, which is a long-standing issue in reptiles. Analysis of Brachyury expression also highlights the presence of two distinct phases, less easily recognizable in model organisms and respectively characterized by an early ring-shaped and a later bilateral symmetrical territory. Systematic comparisons with tetrapod model organisms lead to new insights into the relationships of the blastopore/blastoporal plate system shared by all reptiles, with the blastopore of amphibians and the primitive streak of birds and mammals. The biphasic Brachyury expression pattern is also consistent with recent models of emergence of bilateral symmetry, which raises the question of its evolutionary significance.
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Knack BA, Iguchi A, Shinzato C, Hayward DC, Ball EE, Miller DJ. Unexpected diversity of cnidarian integrins: expression during coral gastrulation. BMC Evol Biol 2008; 8:136. [PMID: 18466626 PMCID: PMC2397394 DOI: 10.1186/1471-2148-8-136] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2007] [Accepted: 05/09/2008] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Adhesion mediated through the integrin family of cell surface receptors is central to early development throughout the Metazoa, playing key roles in cell-extra cellular matrix adhesion and modulation of cadherin activity during the convergence and extension movements of gastrulation. It has been suggested that Caenorhabditis elegans, which has a single beta and two alpha integrins, might reflect the ancestral integrin complement. Investigation of the integrin repertoire of anthozoan cnidarians such as the coral Acropora millepora is required to test this hypothesis and may provide insights into the original roles of these molecules. RESULTS Two novel integrins were identified in Acropora. AmItgalpha1 shows features characteristic of alpha integrins lacking an I-domain, but phylogenetic analysis gives no clear indication of its likely binding specificity. AmItgbeta2 lacks consensus cysteine residues at positions 8 and 9, but is otherwise a typical beta integrin. In situ hybridization revealed that AmItgalpha1, AmItgbeta1, and AmItgbeta2 are expressed in the presumptive endoderm during gastrulation. A second anthozoan, the sea anemone Nematostella vectensis, has at least four beta integrins, two resembling AmItgbeta1 and two like AmItgbeta2, and at least three alpha integrins, based on its genomic sequence. CONCLUSION In two respects, the cnidarian data do not fit expectations. First, the cnidarian integrin repertoire is more complex than predicted: at least two betas in Acropora, and at least three alphas and four betas in Nematostella. Second, whereas the bilaterian alphas resolve into well-supported groups corresponding to those specific for RGD-containing or laminin-type ligands, the known cnidarian alphas are distinct from these. During early development in Acropora, the expression patterns of the three known integrins parallel those of amphibian and echinoderm integrins.
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Affiliation(s)
- Brent A Knack
- ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Queensland, 4811, Australia.
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Blomberg L, Hashizume K, Viebahn C. Blastocyst elongation, trophoblastic differentiation, and embryonic pattern formation. Reproduction 2008; 135:181-95. [DOI: 10.1530/rep-07-0355] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The molecular basis of ungulate and non-rodent conceptus elongation and gastrulation remains poorly understood; however, use of state-of-the-art genomic technologies is beginning to elucidate the mechanisms regulating these complicated processes. For instance, transcriptome analysis of elongating porcine concepti indicates that protein synthesis and trafficking, cell growth and proliferation, and cellular morphology are major regulated processes. Furthermore, potential autocrine roles of estrogen and interleukin-1-β in regulating porcine conceptus growth and remodeling and metabolism have become evident. The importance of estrogen in pig is emphasized by the altered expression of essential steroidogenic and trophoblast factors in lagging ovoid concepti. In ruminants, the characteristic mononucleate trophoblast cells differentiate into a second lineage important for implantation, the binucleate trophoblast, and transcriptome profiling of bovine concepti has revealed a gene cluster associated with rapid trophoblast proliferation and differentiation. Gene cluster analysis has also provided evidence of correlated spatiotemporal expression and emphasized the significance of the bovine trophoblast cell lineage and the regulatory mechanism of trophoblast function. As a part of the gastrulation process in the mammalian conceptus, specification of the germ layers and hence definitive body axes occur in advance of primitive streak formation. Processing of the transforming growth factor-β-signaling molecules nodal and BMP4 by specific proteases is emerging as a decisive step in the initial patterning of the pre-gastrulation embryo. The topography of expression of these and other secreted molecules with reference to embryonic and extraembryonic tissues determines their local interaction potential. Their ensuing signaling leads to the specification of axial epiblast and hypoblast compartments through cellular migration and differentiation and, in particular, the specification of the early germ layer tissues in the epiblast via gene expression characteristic of endoderm and mesoderm precursor cells.
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Abstract
Proper cell-cell communication is necessary to orchestrate the cell fate determination, proliferation, movement, and differentiation that occurs during the development of a complex, multicellular organism. Members of the Wnt family of secreted signaling molecules regulate these processes in virtually every embryonic tissue and during the homeostatic maintenance of adult tissues. Mammalian genetic studies have been particularly useful in illustrating the specific roles that Wnt signaling pathways play in embryonic development, and in the etiology of diseases such as cancer. This chapter will largely focus on the functional roles that Wnts, signaling through the Wnt/-catenin pathway, play during early mammalian development.
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Affiliation(s)
- Terry P Yamaguchi
- Cancer and Developmental Biology Laboratory, Center for Cancer Research, National Cancer Institute-Frederick, the National Institutes of Health, Frederick, MD, USA
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Ueda Y, Yamaguchi R, Ikawa M, Okabe M, Morii E, Maeda Y, Kinoshita T. PGAP1 knock-out mice show otocephaly and male infertility. J Biol Chem 2007; 282:30373-80. [PMID: 17711852 DOI: 10.1074/jbc.m705601200] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
A palmitate linked to the inositol in glycosylphosphatidylinositol (GPI) is removed in the endoplasmic reticulum immediately after the conjugation of GPI with proteins in most cells. Previously, we identified PGAP1 (post GPI attachment to proteins 1) as a GPI inositoldeacylase that removes the palmitate from inositol. A defect in PGAP1 caused a delay in the transport of GPI-anchored proteins (GPI-APs) from the endoplasmic reticulum to the cell surface in Chinese hamster ovary cells, although the cell-surface expression of GPI-APs in the steady state was normal. Nevertheless, in most cells, GPI-APs undergo deacylation. To elucidate the biological significance of PGAP1 in vivo, we established PGAP1 knock-out mice. Most PGAP1 knock-out mice showed otocephaly, a developmental defect, and died right after birth. However, some survived with growth retardation. Male knock-out mice showed severely reduced fertility despite the capability of ejaculation. Their spermatozoa were normal in number, motility, and ability to ascend the uterus, but were unable to go into the oviduct. In vitro, PGAP1-deficient spermatozoa showed weak attachment to the zona pellucida and a severely diminished rate of fertilization. Therefore, an extra acyl chain in GPI anchors caused severe deleterious effects to development and sperm function.
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Affiliation(s)
- Yasutaka Ueda
- Department of Immunoregulation, Osaka University, Osaka, Japan
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56
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Furushima K, Yamamoto A, Nagano T, Shibata M, Miyachi H, Abe T, Ohshima N, Kiyonari H, Aizawa S. Mouse homologues of Shisa antagonistic to Wnt and Fgf signalings. Dev Biol 2007; 306:480-92. [PMID: 17481602 DOI: 10.1016/j.ydbio.2007.03.028] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2006] [Revised: 03/12/2007] [Accepted: 03/19/2007] [Indexed: 12/28/2022]
Abstract
In an effort to identify Otx2 targets in mouse anterior neuroectoderm we identified a gene, mShisa, which is homologous to xShisa1 that we previously reported as a head inducer in Xenopus. mShisa encodes an antagonist against both Wnt and Fgf signalings; it inhibits these signalings cell-autonomously as xShisa1 does. The mShisa expression is lost or greatly reduced in Otx2 mutant visceral endoderm, anterior mesendoderm and anterior neuroectoderm. However, mShisa mutants exhibited no defects in head development. Shisa is composed of five subfamilies, but normal head development in mShisa mutants is unlikely to be explained in terms of the compensation of mShisa deficiency by its paralogues or by known Wnt antagonists in anterior visceral endoderm and/or anterior mesendoderm.
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Affiliation(s)
- Kenryo Furushima
- Laboratory for Animal Resources and Genetic Engineering, Center for Developmental Biology (CDB), RIKEN Kobe, 2-2-3 Minatojima Minami, Chuo-ku, Kobe 650-0047, Japan
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57
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Abstract
During early mouse embryogenesis, temporal and spatial regulation of gene expression and cell signalling influences lineage specification, embryonic polarity, the patterning of tissue progenitors and the morphogenetic movement of cells and tissues. Uniquely in mammals, the extraembryonic tissues are the source of signals for lineage specification and tissue patterning. Here we discuss recent discoveries about the lead up to gastrulation, including early manifestations of asymmetry, coordination of cell and tissue movements and the interactions of transcription factors and signalling activity for lineage allocation and germ-layer specification.
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Affiliation(s)
- Patrick P L Tam
- Embryology Unit, Children's Medical Research Institute and Faculty of Medicine, University of Sydney, Westmead, NSW 2145, Australia.
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Novel gene expression patterns along the proximo-distal axis of the mouse embryo before gastrulation. BMC DEVELOPMENTAL BIOLOGY 2007; 7:8. [PMID: 17302988 PMCID: PMC1821012 DOI: 10.1186/1471-213x-7-8] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/02/2006] [Accepted: 02/15/2007] [Indexed: 01/29/2023]
Abstract
BACKGROUND To date, the earliest stage at which the orientation of the anterior-posterior axis in the mouse embryo is distinguishable by asymmetric gene expression is shortly after E5.5. At E5.5, prospective anterior markers are expressed at the distal tip of the embryo, whereas prospective posterior markers are expressed more proximally, close to the boundary with the extraembryonic region. RESULTS To contribute to elucidating the mechanisms underlying the events involved in early patterning of the mouse embryo, we have carried out a microarray screen to identify novel genes that are differentially expressed between the distal and proximal parts of the E5.5 embryo. Secondary screening of resulting candidates by in situ hybridisation at E5.5 and E6.5 revealed novel expression patterns for known and previously uncharacterised genes, including Peg10, Ctsz1, Cubilin, Jarid1b, Ndrg1, Sfmbt2, Gjb5, Talia and Plet1. The previously undescribed gene Talia and recently identified Plet1 are expressed specifically in the distal-most part of the extraembryonic ectoderm, adjacent to the epiblast, and are therefore potential candidates for regulating early patterning events. Talia and the previously described gene XE7 define a gene family highly conserved among metazoans and with a predicted protein structure suggestive of a post-transcriptional regulative function, whilst Plet1 appears to be mammal-specific and of unknown function. CONCLUSION Our approach has allowed us to compare expression between dissected parts of the egg cylinder and has identified multiple genes with novel expression patterns at this developmental stage. These genes are potential candidates for regulating tissue interactions following implantation.
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Pfister S, Steiner KA, Tam PPL. Gene expression pattern and progression of embryogenesis in the immediate post-implantation period of mouse development. Gene Expr Patterns 2007; 7:558-73. [PMID: 17331809 DOI: 10.1016/j.modgep.2007.01.005] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2006] [Revised: 01/17/2007] [Accepted: 01/22/2007] [Indexed: 10/23/2022]
Abstract
During development of the mouse conceptus from implantation to the early gastrula stage, a multitude of genes encoding structural proteins, transcription factors and components of signalling pathways are expressed in the extraembryonic and embryonic tissues derived from the trophectoderm and the inner cell mass. Some genes are expressed widely in the extraembryonic ectoderm, the visceral endoderm or the epiblast, while others display more restricted expression domains in these tissues or are expressed upon the specification of the germ layers at gastrulation. Overall, the developmental changes in gene expression mirror key events of embryogenesis, and reveal the regionalization of signalling activity and the emergence of tissue patterning.
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Affiliation(s)
- Sabine Pfister
- Embryology Unit, Children's Medical Research Institute, University of Sydney, Locked Bag 23, Wentworthville, NSW 2145, Australia
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60
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Evolution of the mechanisms and molecular control of endoderm formation. Mech Dev 2007; 124:253-78. [PMID: 17307341 DOI: 10.1016/j.mod.2007.01.001] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2006] [Revised: 12/24/2006] [Accepted: 01/03/2007] [Indexed: 01/13/2023]
Abstract
Endoderm differentiation and movements are of fundamental importance not only for subsequent morphogenesis of the digestive tract but also to enable normal patterning and differentiation of mesoderm- and ectoderm-derived organs. This review defines the tissues that have been called endoderm in different species, their cellular origin and their movements. We take a comparative approach to ask how signaling pathways leading to embryonic and extraembryonic endoderm differentiation have emerged in different organisms, how they became integrated and point to specific gaps in our knowledge that would be worth filling. Lastly, we address whether the gastrulation movements that lead to endoderm internalization are coupled with its differentiation.
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61
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Depew MJ, Simpson CA. 21st century neontology and the comparative development of the vertebrate skull. Dev Dyn 2006; 235:1256-91. [PMID: 16598716 DOI: 10.1002/dvdy.20796] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Classic neontology (comparative embryology and anatomy), through the application of the concept of homology, has demonstrated that the development of the gnathostome (jawed vertebrate) skull is characterized both by a fidelity to the gnathostome bauplan and the exquisite elaboration of final structural design. Just as homology is an old concept amended for modern purposes, so are many of the questions regarding the development of the skull. With due deference to Geoffroy-St. Hilaire, Cuvier, Owen, Lankester et al., we are still asking: How are bauplan fidelity and elaboration of design maintained, coordinated, and modified to generate the amazing diversity seen in cranial morphologies? What establishes and maintains pattern in the skull? Are there universal developmental mechanisms underlying gnathostome autapomorphic structural traits? Can we detect and identify the etiologies of heterotopic (change in the topology of a developmental event), heterochronic (change in the timing of a developmental event), and heterofacient (change in the active capacetence, or the elaboration of capacity, of a developmental event) changes in craniofacial development within and between taxa? To address whether jaws are all made in a like manner (and if not, then how not), one needs a starting point for the sake of comparison. To this end, we present here a "hinge and caps" model that places the articulation, and subsequently the polarity and modularity, of the upper and lower jaws in the context of cranial neural crest competence to respond to positionally located epithelial signals. This model expands on an evolving model of polarity within the mandibular arch and seeks to explain a developmental patterning system that apparently keeps gnathostome jaws in functional registration yet tractable to potential changes in functional demands over time. It relies upon a system for the establishment of positional information where pattern and placement of the "hinge" is driven by factors common to the junction of the maxillary and mandibular branches of the first arch and of the "caps" by the signals emanating from the distal-most first arch midline and the lamboidal junction (where the maxillary branch meets the frontonasal processes). In this particular model, the functional registration of jaws is achieved by the integration of "hinge" and "caps" signaling, with the "caps" sharing at some critical level a developmental history that potentiates their own coordination. We examine the evidential foundation for this model in mice, examine the robustness with which it can be applied to other taxa, and examine potential proximate sources of the signaling centers. Lastly, as developmental biologists have long held that the anterior-most mesendoderm (anterior archenteron roof or prechordal plate) is in some way integral to the normal formation of the head, including the cranial skeletal midlines, we review evidence that the seminal patterning influences on the early anterior ectoderm extend well beyond the neural plate and are just as important to establishing pattern within the cephalic ectoderm, in particular for the "caps" that will yield medial signaling centers known to coordinate jaw development.
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Affiliation(s)
- Michael J Depew
- Department of Craniofacial Development, King's College London, Guy's Hospital, London Bridge, London, United Kingdom.
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Luxardi G, Galli A, Forlani S, Lawson K, Maina F, Dono R. Glypicans are differentially expressed during patterning and neurogenesis of early mouse brain. Biochem Biophys Res Commun 2006; 352:55-60. [PMID: 17107664 DOI: 10.1016/j.bbrc.2006.10.185] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2006] [Accepted: 10/26/2006] [Indexed: 10/23/2022]
Abstract
Glypicans are essential modulators of cell signalling during embryogenesis. Little is known about their functions in brain development. We show here that mouse glypicans (gpc-1 to gpc-6) are differentially expressed in embryonic brains during key morphogenetic events. In gastrulating embryos, gpc-4 is the only glypican expressed in anterior visceral endoderm. During neural tube closure, gpc-4 transcripts are restricted to the anterior neural ridge and telencephalon. At this stage, gpc-1 expression shifts from trunk and head mesenchyme to neural tube. Gpc-3 mRNA appears across the ventral neural tube, then in the lamina terminalis and hypothalamus. Gpc-2 and gpc-6 transcripts are in all brain compartments. Gpc-5 is found in ventral brains as neurogenesis starts. Onset of neurogenesis also coincides with differential expression of glypican genes either in neural progenitors or in differentiating neurons. The novel expression sites of glypicans shown here contribute to the identification of signalling molecules involved in brain patterning.
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Affiliation(s)
- Guillaume Luxardi
- IBDML-CNRS UMR 6216, INSERM UMR623, Campus de Luminy, Case 907, 13288 Marseille Cedex 09, France
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Albazerchi A, Stern CD. A role for the hypoblast (AVE) in the initiation of neural induction, independent of its ability to position the primitive streak. Dev Biol 2006; 301:489-503. [PMID: 17010966 DOI: 10.1016/j.ydbio.2006.08.057] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2006] [Revised: 07/29/2006] [Accepted: 08/23/2006] [Indexed: 10/24/2022]
Abstract
The mouse anterior visceral endoderm (AVE) has been implicated in embryonic polarity: it helps to position the primitive streak and some have suggested that it might act as a "head organizer", inducing forebrain directly. Here we explore the role of the hypoblast (the chick equivalent of the AVE) in the early steps of neural induction and patterning. We report that the hypoblast can induce a set of very early markers that are later expressed in the nervous system and in the forebrain, but only transiently. Different combinations of signals are responsible for different aspects of this early transient induction: FGF initiates expression of Sox3 and ERNI, retinoic acid can induce Cyp26A1 and only a combination of low levels of FGF8 together with Wnt- and BMP-antagonists can induce Otx2. BMP- and Wnt-antagonists and retinoic acid, in different combinations, can maintain the otherwise transient induction of these markers. However, neither the hypoblast nor any of these factors or combinations thereof can induce the definitive neural marker Sox2 or the formation of a mature neural plate or a forebrain, suggesting that the hypoblast is not a head organizer and that other signals remain to be identified. Interestingly, FGF and retinoids, generally considered as caudalizing factors, are shown here to play a role in the induction of a transient "pre-neural/pre-forebrain" state.
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Affiliation(s)
- Amanda Albazerchi
- Department of Anatomy and Developmental Biology, University College London, Gower Street, London WC1E 6BT, UK
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Abe Y, Chen W, Huang W, Nishino M, Li YP. CNBP regulates forebrain formation at organogenesis stage in chick embryos. Dev Biol 2006; 295:116-27. [PMID: 16626683 DOI: 10.1016/j.ydbio.2006.03.012] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2004] [Revised: 01/15/2006] [Accepted: 03/13/2006] [Indexed: 11/17/2022]
Abstract
We recently demonstrated that Cellular Nucleic acid Binding Protein (CNBP)(-/-) mouse embryos exhibit forebrain truncation due to a lack of proper morphogenetic movements of the anterior visceral endoderm (AVE) during pre-gastrulation stage (Chen, W., Liang, Y., Deng, W., Shimizu, K., Ashique, A.M., Li, E., Li, Y.P., 2003. The zinc-finger protein CNBP is required for forebrain formation in the mouse, Development 130, 1367-1379). However, CNBP expression pattern in the mouse forebrain suggests that CNBP may have more direct effects during forebrain development. Our data show that CNBP is expressed in tissues of early chick embryo that are the equivalent to the mouse embryo. Using a combination of RNAi-silencing and Retrovirus-misexpression approaches, we investigated the temporal function of CNBP in the specification/development of the chick forebrain during organogenesis. The silencing of CNBP expression resulted in forebrain truncation and the absence of BF-1, Six3 and Hesx1 expression, but not Otx2 in chick embryos. Misexpression of CNBP induced the expression of BF-1, Six3 and Hesx1 in the hindbrain, but not the expression of Otx2. These results offer novel insights into the function of CNBP during organogenesis as the regulator of forebrain formation and a number of rostral head transcription factors. Moreover, CNBP and Otx2 may play roles as regulators of forebrain formation in two parallel pathways. These new insights into CNBP functions underscore the essential role of CNBP in forebrain formation during chick embryo organogenesis.
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Affiliation(s)
- Yoko Abe
- Department of Cytokine Biology, The Forsyth Institute, Boston, MA 02115, USA
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Ware SM, Harutyunyan KG, Belmont JW. Zic3 is critical for early embryonic patterning during gastrulation. Dev Dyn 2006; 235:776-85. [PMID: 16397896 DOI: 10.1002/dvdy.20668] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Mutations in the zinc finger transcription factor ZIC3 are associated with human left-right patterning abnormalities (X-linked heterotaxy, HTX1, MIM 306955), and mice null for Zic3 show a similar phenotype. However, the developmental function of Zic3 is largely unknown and its expression in early embryonic development suggests a role prior to organ formation. The current study of Zic3 null mice identifies a novel function for Zic3 in the gastrula-stage embryo. Analysis of Zic3 function at early embryonic stages shows that it ensures the fidelity of embryonic patterning, including patterning of the anterior visceral endoderm, the initiation of gastrulation, and positioning of the primitive streak. At later stages, deficiency of Zic3 results in abnormal mesoderm allocation. These results indicate a requirement for Zic3 during early embryogenesis prior to cardiac and visceral organ patterning.
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Affiliation(s)
- Stephanie M Ware
- Department of Pediatrics, Cincinnati Children's Hospital Medical Center, University of Cincinnati College of Medicine, Cincinnati, Ohio 45229, USA.
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Richardson L, Torres-Padilla ME, Zernicka-Goetz M. Regionalised signalling within the extraembryonic ectoderm regulates anterior visceral endoderm positioning in the mouse embryo. Mech Dev 2006; 123:288-96. [PMID: 16517131 DOI: 10.1016/j.mod.2006.01.004] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2005] [Revised: 01/17/2006] [Accepted: 01/22/2006] [Indexed: 11/26/2022]
Abstract
The development of the anterior-posterior (AP) axis in the mammalian embryo is controlled by interactions between embryonic and extraembryonic tissues. It is well established that one of these extraembryonic tissues, the anterior visceral endoderm (AVE), can repress posterior cell fate and that signalling from the other, the extraembryonic ectoderm (ExE), is required for posterior patterning. Here, we show that signals from the prospective posterior ExE repress AVE gene expression and affect the distribution of the AVE cells. Surgical ablation of the prospective posterior, but not the anterior, extraembryonic region at 5.5 days of development (E5.5) perturbs the characteristic distal-to-anterior distribution of AVE cells and leads to a dramatic expansion of the AVE domain. Time-lapse imaging studies show that this increase is due to the ectopic expression of an AVE marker, which results in a symmetrical positioning of the AVE. Surgical ablation of this same ExE region after the distal-to-anterior migration has already commenced, at E5.75, does not affect the localisation of the AVE, indicating that this effect takes place within a short time window. Conversely, transplanting the prospective posterior, but not the anterior, extraembryonic region onto isolated E5.5 embryonic explants drastically reduces the AVE domain. Further, transplantation experiments demonstrate that the signalling regulating AVE gene expression originates from the posterior ExE, rather than its surrounding VE. Together, our results show that signals emanating from the future posterior ExE within a temporal window both restrict the AVE domain and promote its specific positioning. This indicates for the first time that the ExE is already regionalised a day before the onset of gastrulation in order to correctly set the orientation of the AP axis of the mouse embryo. We propose a reciprocal function of the posterior ExE and the AVE in establishing a balance between the antagonistic activities of these two tissues, essential for AP patterning.
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Affiliation(s)
- Lucy Richardson
- The Wellcome Trust/Cancer Research UK Gurdon Institute, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
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Dickinson K, Leonard J, Baker JC. Genomic profiling of mixer and Sox17beta targets during Xenopus endoderm development. Dev Dyn 2006; 235:368-81. [PMID: 16278889 PMCID: PMC4510981 DOI: 10.1002/dvdy.20636] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The transcription factors Mixer and Sox17beta have well-characterized roles in endoderm specification during Xenopus embryogenesis. In order to more thoroughly understand the mechanisms by which these endodermal regulators act, we expressed Mixer and Sox17beta in naïve ectodermal tissue and, using oligonucleotide-based microarrays, compared their genomic transcriptional profile to that of unaffected tissue. Using this approach, we identified 71 transcripts that are upregulated by Mixer or Sox17beta, 63 of which have previously uncharacterized roles in endoderm development. Furthermore, an in situ hybridization screen using antisense probes for several of these clones identified six targets of Mixer and/or Sox17beta that are expressed in the endoderm during gastrula stages, providing new and regional markers of the endoderm. Our results contribute further insight into the functions of Mixer and Sox17beta and bring us closer to understanding at the molecular level the pathways that regulate endoderm development.
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Affiliation(s)
| | | | - Julie C. Baker
- Corresponding Author, Julie C. Baker, Genetics Department, Stanford University, 300 Pasteur Drive, MC 5120, Stanford, CA 94062, 650-723-1082, 650-725-1534 (fax),
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Bohnsack BL, Lai L, Northrop JL, Justice MJ, Hirschi KK. Visceral endoderm function is regulated byquaking and required for vascular development. Genesis 2006; 44:93-104. [PMID: 16470614 DOI: 10.1002/gene.20189] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The quaking (qkI) gene produces three major alternatively spliced variants (qkI-5,-6,-7) that encode for proteins that share the RNA binding, KH domain. Previous studies utilizing the qk(k2) allele, which contains an N-ethyl-N-nitrosourea (ENU)-induced point mutation in the KH domain, demonstrate that this functional region of qkI is required for embryonic vascular development. In the current studies we demonstrate that qk(l-1)/qk(l-1) mutants, which lack the QKI-5 splice variant, also died at midgestation due to vascular remodeling defects. In addition, although all three QKI isoforms were expressed in the visceral endoderm of wildtype yolk sacs, qkI-6 and qkI-7 transcript and protein expression were suppressed in qk(k2)/qk(k2) and qk(l-1)/qk(l-1) mutant yolk sacs, suggesting that the KH-domain of QKI-5 was required for qkI-6 and qkI-7 expression. Further studies revealed that the cellular role of qkI is to regulate visceral endoderm function, including the local synthesis of retinoic acid (RA) and the subsequent control of endothelial cell proliferation, matrix production, and visceral endoderm survival. Although these defects were rescued by exogenous RA, visceral endoderm function or vascular remodeling were not restored. Thus, we conclude that qkI regulates visceral endoderm function, which is critical for vascular remodeling.
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Affiliation(s)
- Brenda L Bohnsack
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030, USA
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69
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Abstract
The Anterior Visceral Endoderm is an extraembryonic tissue that plays a pivotal role during embryogenesis, being responsible for the proper orientation of the anterior-posterior axis of the embryo and for appropriate pattering of adjacent embryonic tissue. In this review I discuss the formation and migration of the AVE, and attempt to place some recent findings in the context of a working model.
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Affiliation(s)
- Shankar Srinivas
- Department of Physiology, Anatomy & Genetics, University of Oxford, Oxford, United Kingdom.
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70
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Kimura-Yoshida C, Nakano H, Okamura D, Nakao K, Yonemura S, Belo JA, Aizawa S, Matsui Y, Matsuo I. Canonical Wnt Signaling and Its Antagonist Regulate Anterior-Posterior Axis Polarization by Guiding Cell Migration in Mouse Visceral Endoderm. Dev Cell 2005; 9:639-50. [PMID: 16256739 DOI: 10.1016/j.devcel.2005.09.011] [Citation(s) in RCA: 141] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2004] [Revised: 04/28/2005] [Accepted: 09/22/2005] [Indexed: 11/28/2022]
Abstract
The mouse embryonic axis is initially formed with a proximal-distal orientation followed by subsequent conversion to a prospective anterior-posterior (A-P) polarity with directional migration of visceral endoderm cells. Importantly, Otx2, a homeobox gene, is essential to this developmental process. However, the genetic regulatory mechanism governing axis conversion is poorly understood. Here, defective axis conversion due to Otx2 deficiency can be rescued by expression of Dkk1, a Wnt antagonist, or following removal of one copy of the beta-catenin gene. Misexpression of a canonical Wnt ligand can also inhibit correct A-P axis rotation. Moreover, asymmetrical distribution of beta-catenin localization is impaired in the Otx2-deficient and Wnt-misexpressing visceral endoderm. Concurrently, canonical Wnt and Dkk1 function as repulsive and attractive guidance cues, respectively, in the migration of visceral endoderm cells. We propose that Wnt/beta-catenin signaling mediates A-P axis polarization by guiding cell migration toward the prospective anterior in the pregastrula mouse embryo.
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Affiliation(s)
- Chiharu Kimura-Yoshida
- Vertebrate Body Plan Group, RIKEN Center for Developmental Biology (CDB), 2-2-3 Minatojima-minami-cho, Chuou-ku Kobe, Hyogo 650-0047, Japan
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71
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Acampora D, Annino A, Tuorto F, Puelles E, Lucchesi W, Papalia A, Simeone A. Otx genes in the evolution of the vertebrate brain. Brain Res Bull 2005; 66:410-20. [PMID: 16144623 DOI: 10.1016/j.brainresbull.2005.02.005] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2004] [Indexed: 12/01/2022]
Abstract
Only until a decade ago, animal phylogeny was traditionally based on the assumption that evolution of bilaterians went from simple to complex through gradual steps in which the extant species would represent grades of intermediate complexity that reflect the organizational levels of their ancestors. The advent of more sophisticated molecular biology techniques combined to an increasing variety of functional experiments has provided new tools, which lead us to consider evolutionary studies under a brand new light. An ancestral versus derived low-complexity of a given organism has now to be carefully re-assessed and also the molecular data so far accumulated needs to be re-evaluated. Conserved gene families expressed in the nervous system of all the species have been extensively used to reconstruct evolutionary steps, which may lead to identify the morphological as well as molecular features of the last common ancestor of bilaterians (Urbilateria). The Otx gene family is among these and will be here reviewed.
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Affiliation(s)
- Dario Acampora
- MRC Centre for Developmental Neurobiology, New Hunt's House, 4th Floor, King's College London, UK
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72
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Woda JM, Calzonetti T, Hilditch-Maguire P, Duyao MP, Conlon RA, MacDonald ME. Inactivation of the Huntington's disease gene (Hdh) impairs anterior streak formation and early patterning of the mouse embryo. BMC DEVELOPMENTAL BIOLOGY 2005; 5:17. [PMID: 16109169 PMCID: PMC1208873 DOI: 10.1186/1471-213x-5-17] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/21/2005] [Accepted: 08/18/2005] [Indexed: 12/01/2022]
Abstract
Background Huntingtin, the HD gene encoded protein mutated by polyglutamine expansion in Huntington's disease, is required in extraembryonic tissues for proper gastrulation, implicating its activities in nutrition or patterning of the developing embryo. To test these possibilities, we have used whole mount in situ hybridization to examine embryonic patterning and morphogenesis in homozygous Hdhex4/5 huntingtin deficient embryos. Results In the absence of huntingtin, expression of nutritive genes appears normal but E7.0–7.5 embryos exhibit a unique combination of patterning defects. Notable are a shortened primitive streak, absence of a proper node and diminished production of anterior streak derivatives. Reduced Wnt3a, Tbx6 and Dll1 expression signify decreased paraxial mesoderm and reduced Otx2 expression and lack of headfolds denote a failure of head development. In addition, genes initially broadly expressed are not properly restricted to the posterior, as evidenced by the ectopic expression of Nodal, Fgf8 and Gsc in the epiblast and T (Brachyury) and Evx1 in proximal mesoderm derivatives. Despite impaired posterior restriction and anterior streak deficits, overall anterior/posterior polarity is established. A single primitive streak forms and marker expression shows that the anterior epiblast and anterior visceral endoderm (AVE) are specified. Conclusion Huntingtin is essential in the early patterning of the embryo for formation of the anterior region of the primitive streak, and for down-regulation of a subset of dynamic growth and transcription factor genes. These findings provide fundamental starting points for identifying the novel cellular and molecular activities of huntingtin in the extraembryonic tissues that govern normal anterior streak development. This knowledge may prove to be important for understanding the mechanism by which the dominant polyglutamine expansion in huntingtin determines the loss of neurons in Huntington's disease.
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Affiliation(s)
- Juliana M Woda
- Molecular Neurogenetics Unit, Center for Human Genetic Research, Massachusetts General Hospital, CNY-149, 13th Street, Charlestown MA 02129, USA
| | - Teresa Calzonetti
- Molecular Neurogenetics Unit, Center for Human Genetic Research, Massachusetts General Hospital, CNY-149, 13th Street, Charlestown MA 02129, USA
| | | | - Mabel P Duyao
- Department of Pathology, Harvard Medical School, 77 Avenue Louis Pasteur, NRB-850A, Boston MA 02115, USA
| | - Ronald A Conlon
- Department of Genetics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Marcy E MacDonald
- Molecular Neurogenetics Unit, Center for Human Genetic Research, Massachusetts General Hospital, CNY-149, 13th Street, Charlestown MA 02129, USA
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73
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Chiao E, Leonard J, Dickinson K, Baker JC. High-throughput functional screen of mouse gastrula cDNA libraries reveals new components of endoderm and mesoderm specification. Genome Res 2005; 15:44-53. [PMID: 15632089 PMCID: PMC540274 DOI: 10.1101/gr.2993405] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
This study describes a cross-species functional screen of mouse gastrula cDNA libraries for components of endoderm and mesoderm specification. Pools of 96 cDNAs from arrayed mouse gastrula cDNA libraries were transcribed into mRNA and injected into either the presumptive mesoderm or the ectoderm of one-cell Xenopus laevis embryos. Injected embryos were examined at gastrula stage by in situ hybridization with endoderm or mesoderm markers. Using this approach, we screened over 700 pools or approximately 60,000 cDNAs. We identified 17 unique cDNAs that function during mesoderm and/or endoderm specification and 16 that cause general morphology changes. Identified molecules fall into eight general functional groups as follows: cell cycle components (seven), transcription factors (four), extracellular secreted molecules (seven), transmembrane receptors (one), intracellular signaling components (five), microtubule components (two), metabolism molecules (three), and unknown (four). Several of the genes we identified would not have been predicted to be involved in endoderm or mesoderm specification, highlighting the usefulness of nonbiased screening approaches. This includes Otx2, which we show is a downstream target of Xsox17beta. The speed, low cost, and high efficiency of this cross-species screen makes it an ideal method for examining cDNAs from difficult-to-obtain sources. Therefore, this approach complements the current mouse molecular genetics systems and provides a powerful means for the genome-wide examination of mammalian gene function.
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Affiliation(s)
- Eric Chiao
- Department of Genetics, Stanford University Medical School, Stanford, California 94062, USA
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74
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Wada S, Sudou N, Saiga H. Roles of Hroth, the ascidian otx gene, in the differentiation of the brain (sensory vesicle) and anterior trunk epidermis in the larval development of Halocynthia roretzi. Mech Dev 2005; 121:463-74. [PMID: 15147764 DOI: 10.1016/j.mod.2004.03.017] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2003] [Revised: 02/17/2004] [Accepted: 03/25/2004] [Indexed: 10/26/2022]
Abstract
Otx genes are expressed in the anterior neural tube and endoderm in all of the chordates so far examined. In mouse embryos, important roles of otx genes in the brain development have been well documented. However, roles of otx genes in other chordate species have been less characterized. To advance our understanding about roles of otx genes in chordates, we have studied Hroth, otx of the ascidian, Halocynthia roretzi. Hroth is expressed in the anterior part of the neural tube (the sensory vesicle), the endoderm and anterior epidermis in the development. In this study, we investigated roles of Hroth in the larval development through an antisense morpholino oligonucleotides (MOs) approach. Embryos injected with Hroth-targeting MO (Hroth knockdown embryos) developed into larvae without the adhesive organ, sensory pigment cells and cavity of the sensory vesicle. The tissues, in which defects were observed, are derived from anterior-animal cells of the embryo in early cleavage stages. During cleavage stages, Hroth is also expressed in the endoderm precursors of the vegetal hemisphere. However, Hroth expression in the anterior endoderm precursors do not seem to be essential for the above defects, since MO injection into the anterior-animal but not anterior-vegetal pair cells at the 8-cell stage gave the defects. Analysis of marker gene expression demonstrated that the fate choice of the sensory vesicle precursors and the specification of the sensory vesicle territory occurred normally, but the subsequent differentiation of the sensory vesicle was severely affected in Hroth knockdown embryos. The anterior trunk epidermis including the adhesive organ-forming region was also affected, indicating that anterior epidermal patterning requires Hroth function. Based on these findings, similarities and differences in the roles of otx genes between ascidians and mice are discussed.
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Affiliation(s)
- Shuichi Wada
- Department of Biological Sciences, Graduate School of Science, Tokyo Metropolitan University, 1-1 Minamiohsawa, Hachiohji, Tokyo 192-0397, Japan
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75
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Vallier L, Reynolds D, Pedersen RA. Nodal inhibits differentiation of human embryonic stem cells along the neuroectodermal default pathway. Dev Biol 2005; 275:403-21. [PMID: 15501227 DOI: 10.1016/j.ydbio.2004.08.031] [Citation(s) in RCA: 282] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2004] [Revised: 08/12/2004] [Accepted: 08/20/2004] [Indexed: 01/04/2023]
Abstract
Genetic studies in fish, amphibia, and mice have shown that deficiency of Nodal signaling blocks differentiation into mesoderm and endoderm. Thus, Nodal is considered as a major inducer of mesendoderm during gastrulation. On this basis, Nodal is a candidate for controlling differentiation of pluripotent human embryonic stem cells (hESCs) into tissue lineages with potential clinical value. We have investigated the effect of Nodal, both as a recombinant protein and as a constitutively expressed transgene, on differentiation of hESCs. When control hESCs were grown in chemically defined medium, their expression of markers of pluripotency progressively decreased, while expression of neuroectoderm markers was strongly upregulated, thus revealing a neuroectodermal default mechanism for differentiation in this system. hESCs cultured in recombinant Nodal, by contrast, showed prolonged expression of pluripotency marker genes and reduced induction of neuroectoderm markers. These Nodal effects were accentuated in hESCs expressing a Nodal transgene, with striking morphogenetic consequences. Nodal-expressing hESCs developing as embryoid bodies contained an outer layer of visceral endoderm-like cells surrounding an inner layer of epiblast-like cells, each layer having distinct gene expression patterns. Markers of neuroectoderm were not upregulated during development of Nodal-expressing embryoid bodies, nor was there induction of markers for definitive mesoderm or endoderm differentiation. Moreover, the inner layer expressed markers of pluripotency, characteristic of undifferentiated hESCs and of epiblast in mouse embryos. These results could be accounted for by an inhibitory effect of Nodal-induced visceral endoderm on pluripotent cell differentiation into mesoderm and endoderm, with a concomitant inhibition of neuroectoderm differentiation by Nodal itself. There could also be a direct effect of Nodal in the maintenance of pluripotency. In summary, analysis of the Nodal-expressing phenotype suggests a function for the transforming growth factor-beta (TGF-beta) growth factor superfamily in pluripotency and in early cell fate decisions leading to primary tissue layers during in vitro development of pluripotent human stem cells. The effects of Nodal on early differentiation illustrate how hESCs can augment mouse embryos as a model for analyzing mechanisms of early mammalian development.
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Affiliation(s)
- Ludovic Vallier
- Department of Surgery, University of Cambridge, Cambridge CB2 2QQ, United Kingdom.
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76
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Furushima K, Murata T, Kiyonari H, Aizawa S. Characterization ofOpr deficiency in mouse brain: Subtle defects in dorsomedial telencephalon and medioventral forebrain. Dev Dyn 2005; 232:1056-61. [PMID: 15736266 DOI: 10.1002/dvdy.20253] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Opr/Zic5 is a zinc-finger gene belonging to, and unique in, the opa/Zic family. Its expression is found in the anterior epiblast and anterior neuroectoderm during gastrulation and early neurulation. Later, we found the expression characteristic in the dorsomedial parts of forebrain and midbrain. However, no defects were apparent in embryonic day 10.5 Opr null mutants, and subtle defects were later found in medial pallium and ventral structures of forebrain, suggesting the compensation of Opr deficiency by its cognate(s).
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Affiliation(s)
- Kenryo Furushima
- Laboratory for Animal Resources and Genetic Engineering, Center for Developmental Biology (CDB), RIKEN Kobe, Kobe, Japan
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77
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Idkowiak J, Weisheit G, Plitzner J, Viebahn C. Hypoblast controls mesoderm generation and axial patterning in the gastrulating rabbit embryo. Dev Genes Evol 2004; 214:591-605. [PMID: 15480760 DOI: 10.1007/s00427-004-0436-y] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2004] [Accepted: 08/16/2004] [Indexed: 10/26/2022]
Abstract
Gastrulation in higher vertebrate species classically commences with the generation of mesoderm cells in the primitive streak by epithelio-mesenchymal transformation of epiblast cells. However, the primitive streak also marks, with its longitudinal orientation in the posterior part of the conceptus, the anterior-posterior (or head-tail) axis of the embryo. Results obtained in chick and mouse suggest that signals secreted by the hypoblast (or visceral endoderm), the extraembryonic tissue covering the epiblast ventrally, antagonise the mesoderm induction cascade in the anterior part of the epiblast and thereby restrict streak development to the posterior pole (and possibly initiate head development anteriorly). In this paper we took advantage of the disc-shape morphology of the rabbit gastrula for defining the expression compartments of the signalling molecules Cerberus and Dickkopf at pre-gastrulation and early gastrulation stages in a mammal other than the mouse. The two molecules are expressed in novel expression compartments in a complementary fashion both in the hypoblast and in the emerging primitive streak. In loss-of-function experiments, carried out in a New-type culturing system, hypoblast was removed prior to culture at defined stages before and at the beginning of gastrulation. The epiblast shows a stage-dependent and topographically restricted susceptibility to express Brachyury, a T-box gene pivotal for mesoderm formation, and to transform into (histologically proven) mesoderm. These results confirm for the mammalian embryo that the anterior-posterior axis of the conceptus is formed first as a molecular prepattern in the hypoblast and then irrevocably fixed, under the control of signals secreted from the hypoblast, by epithelio-mesenchymal transformation (primitive streak formation) in the epiblast.
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Affiliation(s)
- Jan Idkowiak
- Department of Anatomy and Cell Biology, Martin-Luther-University, Grosse Steinstrasse 52, 06097, Halle, Germany
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78
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Abstract
In mammalian embryos, molecular cross-talk with extraembryonic tissues is essential to elaborate the primary body axes. Here, we review a series of reciprocal interactions that occur shortly after implantation in the uterus, and discuss how they are integrated in a complex signaling network to establish antero-posterior and dorso-ventral polarity. At the heart of this signaling network is the TGFbeta-related protein Nodal which acts on extraembryonic tissues to induce positive and negative feedback regulators at opposite poles of the egg cylinder. This likely results in an activity gradient which is instrumental to pattern the embryo proper.
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Affiliation(s)
- Siew-Lan Ang
- Division of Developmental Neurobiology, NIMR, The Ridgeway, Mill Hill, London NW7 1AA, UK.
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79
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Abstract
Embryonic patterning of the mouse during gastrulation and early organogenesis engenders the specification of anterior versus posterior structures and body laterality by the interaction of signalling and modulating activities. A group of cells in the mouse gastrula, characterised by the expression of a repertoire of "organiser" genes, acts as a source and the conduit for allocation of the axial mesoderm, floor plate and definitive endoderm. The organiser and its derivatives provide the antagonistic activity that modulates WNT and TGFbeta signalling. Recent findings show that the organiser activity is augmented by morphogenetic activity of the extraembryonic and embryonic endoderm, suggesting embryonic patterning is not solely the function of the organiser.
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Affiliation(s)
- Lorraine Robb
- The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Vic. 3050, Australia
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80
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Abstract
The main aim of the gastrulation process is commonly regarded to be the generation of the definitive germ layers known as mesoderm, endoderm and ectoderm. Here we discuss how the topography of gene expression, cellular migration and proliferative activity in the preliminary germ layers (hypoblast and epiblast) of the rabbit embryo reveal the sequence of events that establishes the three major body axes. We present a testable model in which a combination of cellular movement in the hypoblast with a morphogen gradient created by the (extraembryonic) trophoblast creates morphological polarity in the embryo and, hence, the co-ordinates for germ layer formation.
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Affiliation(s)
- Jan Idkowiak
- Department of Anatomy and Cell Biology, Martin-Luther University, Grosse Steinstrasse 56, 06097 Halle, Germany
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81
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Lu CC, Robertson EJ. Multiple roles for Nodal in the epiblast of the mouse embryo in the establishment of anterior-posterior patterning. Dev Biol 2004; 273:149-59. [PMID: 15302604 DOI: 10.1016/j.ydbio.2004.06.004] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2004] [Revised: 06/08/2004] [Accepted: 06/10/2004] [Indexed: 11/19/2022]
Abstract
The TGFbeta family member Nodal has been shown to be involved in a variety of processes in development, including early axis formation. Here, we use a conditional gene inactivation strategy to show a specific requirement for Nodal in the epiblast. Complete inactivation of the Nodal locus in the epiblast using the Sox2-Cre deleter strain results in a failure to establish global anterior-posterior patterning, a phenotype that resembles the Nodal null phenotype. By contrast, mosaic inactivation of Nodal in the epiblast using the Mox2-Cre (MORE) deleter strain affects formation of the anterior mesendoderm and subsequent anterior neurectoderm patterning. Furthermore, ES cell chimera experiments indicate that Nodal-deficient ES cells preferentially populate the anterior compartment of the epiblast, suggesting that cell mixing in the epiblast is not random and that Nodal signaling mediates a novel anterior-posterior cell-sorting process within the epiblast before gastrulation.
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Affiliation(s)
- Cindy C Lu
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA
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82
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Mesnard D, Filipe M, Belo JA, Zernicka-Goetz M. The Anterior-Posterior Axis Emerges Respecting the Morphology of the Mouse Embryo that Changes and Aligns with the Uterus before Gastrulation. Curr Biol 2004; 14:184-96. [PMID: 14761650 DOI: 10.1016/j.cub.2004.01.026] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2003] [Revised: 12/24/2003] [Accepted: 12/30/2003] [Indexed: 11/24/2022]
Abstract
BACKGROUND When the anterior-posterior axis of the mouse embryo becomes explicit at gastrulation, it is almost perpendicular to the long uterine axis. This led to the belief that the uterus could play a key role in positioning this future body axis. RESULTS Here, we demonstrate that when the anterior-posterior axis first emerges it does not respect the axes of the uterus but, rather, the morphology of the embryo. Unexpectedly, the emerging anterior-posterior axis is initially aligned not with the long, but the short axis of the embryo. Then whether the embryo develops in vitro or in utero, the anterior-posterior axis becomes aligned with the long axis of embryo just prior to gastrulation. Of three mechanisms that could account for this apparent shift in anterior-posterior axis orientation-cell migration, spatial change of gene expression, or change in embryo shape-lineage tracing studies favor a shape change accompanied by restriction of the expression domain of anterior markers. This property of the embryo must be modulated by interactions with the uterus as ultimately the anterior-posterior and long axes of the embryo align with the left-right uterine axis. CONCLUSIONS The emerging anterior-posterior axis relates to embryo morphology rather than that of the uterus. The apparent shift in its orientation to align with the long embryonic axis and with the uterus is associated with a change in embryo shape and a refinement of anterior gene expression pattern. This suggests an interdependence between anterior-posterior gene expression, the shape of the embryo, and the uterus.
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Affiliation(s)
- Daniel Mesnard
- Wellcome Trust/Cancer Research Gurdon Institute, Tennis Court Road, Cambridge CB2 1QR, United Kingdom
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83
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Shibamoto S, Winer J, Williams M, Polakis P. A blockade in Wnt signaling is activated following the differentiation of F9 teratocarcinoma cells. Exp Cell Res 2004; 292:11-20. [PMID: 14720502 DOI: 10.1016/j.yexcr.2003.08.009] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Aberrant activation of the Wnt signaling pathway is a common event in human tumor progression. Wnt signaling has also been implicated in maintaining a variety of adult and embryonic stem cells by imposing a restraint to differentiation. To understand the effect of Wnt signaling on the differentiation of epithelial cells, we used mouse teratocarcinoma F9 cells as a model. The F9 cells can be differentiated into visceral endoderm (VE) resembling absorptive columnar epithelial cells. We performed comparative gene expression analysis on retinoic acid-differentiated and undifferentiated F9 cells and confirmed that markers of VE and intestinal epithelium were induced upon differentiation. The induction of these markers by retinoic acid was reduced in the presence of Wnt, although Wnt alone did not change their expression. This suggests that Wnt signaling inhibited the differentiation of F9 cells by altering gene expression. This inhibition was also reflected in the morphology of the F9 cells as their apical-basal polarity was disrupted by inclusion of Wnt during differentiation. These results support a model in which Wnt modulates the expression of genes required for normal terminal differentiation of the stem cells. However, it follows that progenitor cells must escape from Wnt signaling to attain the differentiated state. Accordingly, we found that differentiated F9 cells no longer responded to Wnt and that a blockade in Wnt signaling occurred upstream of Axin. Consistent with this, Wnt negative regulators, such as Dickkopf-1 and Disabled-2, were induced upon the differentiation of F9 cells. We propose that a similar system to produce Wnt inhibitors regulates homeostasis of certain stem cell compartments in vivo.
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Affiliation(s)
- Sayumi Shibamoto
- Departments of Molecular Oncology and Molecular Biology, Genentech, Inc, South San Francisco, CA 94080-4918, USA
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84
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DeYoung RA, Baker JC, Cado D, Winoto A. The orphan steroid receptor Nur77 family member Nor-1 is essential for early mouse embryogenesis. J Biol Chem 2003; 278:47104-9. [PMID: 13129926 DOI: 10.1074/jbc.m307496200] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nur77 and its family members, Nor-1 and Nurr1, are orphan steroid receptors implicated in a wide variety of biological processes, including apoptosis and dopamine neuron agenesis. Expression of these family members can be detected at low levels in many tissues but they are expressed at very high levels when cells are stimulated by outside signals, including serum, nerve growth factor, and receptor engagement. Introduction of a dominant negative Nur77 protein that blocks the activities of all family members led to inhibition of apoptosis in T cells. Nur77-deficient mice, however, exhibit no phenotype, and a line of Nor-1 mutant mice was reported to exhibit a mild ear development phenotype but no other gross abnormalities. Here, we report the generation of Nor-1-deficient mice with a block in early embryonic development. Nor-1 is expressed early during embryogenesis, and its loss leads to embryonic lethality around embryonic day 8.5 of gestation. The mutant embryos fail to complete gastrulation and display distinct morphological abnormalities, including a decrease in overall size, developmental delay and an accumulation of mesoderm in the primitive streak during gastrulation. Abnormal expression of a number of early developmental markers and defects in growth or distribution of emerging mesoderm cells were also detected. These data suggest that Nor-1 plays a crucial role in gastrulation.
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Affiliation(s)
- R Andrea DeYoung
- Department of Molecular and Cell Biology, Division of Immunology, University of California at Berkeley, Berkeley, CA 94720-3200, USA
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85
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Robertson EJ, Norris DP, Brennan J, Bikoff EK. Control of early anterior-posterior patterning in the mouse embryo by TGF-beta signalling. Philos Trans R Soc Lond B Biol Sci 2003; 358:1351-7; discussion 1357. [PMID: 14511481 PMCID: PMC1693235 DOI: 10.1098/rstb.2003.1332] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Prior to gastrulation the mouse embryo exists as a symmetrical cylinder consisting of three tissue layers. Positioning of the future anterior-posterior axis of the embryo occurs through coordinated cell movements that rotate a pre-existing proximal-distal (P-D) axis. Overt axis formation becomes evident when a discrete population of proximal epiblast cells become induced to form mesoderm, initiating primitive streak formation and marking the posterior side of the embryo. Over the next 12-24 h the primitive streak gradually elongates along the posterior side of the epiblast to reach the distal tip. The most anterior streak cells comprise the 'organizer' region and include the precursors of the so-called 'axial mesendoderm', namely the anterior definitive endoderm and prechordal plate mesoderm, as well as those cells that give rise to the morphologically patent node. Signalling pathways controlled by the transforming growth factor-beta ligand nodal are involved in orchestrating the process of axis formation. Embryos lacking nodal activity arrest development before gastrulation, reflecting an essential role for nodal in establishing P-D polarity by generating and maintaining the molecular pattern within the epiblast, extraembryonic ectoderm and the visceral endoderm. Using a genetic strategy to manipulate temporal and spatial domains of nodal expression reveals that the nodal pathway is also instrumental in controlling both the morphogenetic movements required for orientation of the final axis and for specification of the axial mesendoderm progenitors.
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Affiliation(s)
- Elizabeth J Robertson
- Department of Molecular and Cellular Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA.
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86
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Abstract
In pregastrula stage mouse embryos, visceral endoderm (VE) migrates from a distal to anterior position to initiate anterior identity in the adjacent epiblast. This anterior visceral endoderm (AVE) is then displaced away from the epiblast by the definitive endoderm to become associated with the extra-embryonic ectoderm and subsequently contributes to the yolk sac. Little is known about the molecules that regulate this proximal displacement. Here we describe a role for mouse angiomotin (amot) in VE movements. amot expression is initially detected in the AVE and subsequently in the VE associated with the extra-embryonic ectoderm. Most amot mutant mice die soon after gastrulation with distinct furrows of VE located at the junction of the embryonic and extra-embryonic regions. Mutant analysis suggests that VE accumulation in these furrows is caused by defects in cell migration into proximal extra-embryonic regions, although distal-to-anterior movements associated with the epiblast, definitive endoderm formation, and anterior specification of the epiblast appear to be normal. These results suggest that amot acts within subregions of the VE to regulate morphogenetic movements that are required for embryo viability.
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Affiliation(s)
- Akihiko Shimono
- Department of Molecular Genetics, University of Texas, M. D. Anderson Cancer Center, Houston, TX 77030, USA
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87
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Lagutin OV, Zhu CC, Kobayashi D, Topczewski J, Shimamura K, Puelles L, Russell HRC, McKinnon PJ, Solnica-Krezel L, Oliver G. Six3 repression of Wnt signaling in the anterior neuroectoderm is essential for vertebrate forebrain development. Genes Dev 2003; 17:368-79. [PMID: 12569128 PMCID: PMC195989 DOI: 10.1101/gad.1059403] [Citation(s) in RCA: 366] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2002] [Accepted: 12/09/2002] [Indexed: 01/20/2023]
Abstract
In vertebrate embryos, formation of anterior neural structures requires suppression of Wnt signals emanating from the paraxial mesoderm and midbrain territory. In Six3(-/-) mice, the prosencephalon was severely truncated, and the expression of Wnt1 was rostrally expanded, a finding that indicates that the mutant head was posteriorized. Ectopic expression of Six3 in chick and fish embryos, together with the use of in vivo and in vitro DNA-binding assays, allowed us to determine that Six3 is a direct negative regulator of Wnt1 expression. These results, together with those of phenotypic rescue of headless/tcf3 zebrafish mutants by mouse Six3, demonstrate that regionalization of the vertebrate forebrain involves repression of Wnt1 expression by Six3 within the anterior neuroectoderm. Furthermore, these results support the hypothesis that a Wnt signal gradient specifies posterior fates in the anterior neural plate.
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Affiliation(s)
- Oleg V Lagutin
- Department of Genetics, St. Jude Children's Research Hospital, Memphis, Tennessee 38105-2794, USA
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88
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Smithers LE, Jones CM. Xhex-expressing endodermal tissues are essential for anterior patterning in Xenopus. Mech Dev 2002; 119:191-200. [PMID: 12464432 DOI: 10.1016/s0925-4773(02)00361-1] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Two regions expressing Hex in the early gastrula contribute to organizing the anterior of the vertebrate embryo. In Xenopus, these include the anterior yolky endoderm and the suprablastoporal endoderm (SBE), which is fated to form the epithelial lining of the gut. These tissues may correspond to the anterior visceral endoderm and anterior definitive endoderm of amniotes. Genetic studies in mice have demonstrated the important roles of these tissues in producing anterior identity in the adjacent neural ectoderm. In Xenopus, both the anterior endoderm and the SBE have anterior inducing properties; furthermore, the SBE can organize a full anterior-posterior axis. Inhibition of Xhex function shows that both these Xhex-expressing endodermal tissues are required for anterior development in Xenopus.
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Affiliation(s)
- Lucy E Smithers
- Section of Gene Function and Regulation, Institute of Cancer Research, 237 Fulham Road, London SW3 6JB, UK
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89
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Beck S, Le Good JA, Guzman M, Ben Haim N, Roy K, Beermann F, Constam DB. Extraembryonic proteases regulate Nodal signalling during gastrulation. Nat Cell Biol 2002; 4:981-5. [PMID: 12447384 DOI: 10.1038/ncb890] [Citation(s) in RCA: 160] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2002] [Revised: 10/24/2002] [Accepted: 10/24/2002] [Indexed: 02/01/2023]
Abstract
During gastrulation, a cascade of inductive tissue interactions converts pre-existing polarity in the mammalian embryo into antero-posterior pattern. This process is triggered by Nodal, a protein related to transforming growth factor-beta (TFG-beta) that is expressed in the epiblast and visceral endoderm, and its co-receptor Cripto, which is induced downstream of Nodal. Here we show that the proprotein convertases Spc1 and Spc4 (also known as Furin and Pace4, respectively) are expressed in adjacent extraembryonic ectoderm. They stimulate Nodal maturation after its secretion and are required in vivo for Nodal signalling. Embryo explants deprived of extraembryonic ectoderm phenocopy Spc1(-/-); Spc4(-/-) double mutants in that endogenous Nodal fails to induce Cripto. But recombinant mature Nodal, unlike uncleaved precursor, can efficiently rescue Cripto expression. Cripto is also expressed in explants treated with bone morphogenetic protein 4 (BMP4). This indicates that Nodal may induce Cripto through both a signalling pathway in the embryo and induction of Bmp4 in the extraembryonic ectoderm. A lack of Spc1 and Spc4 affects both pathways because these proteases also stimulate induction of Bmp4.
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Affiliation(s)
- Séverine Beck
- Developmental Biology Group, Swiss Institute for Experimental Cancer Research (ISREC), Chemin des Boveresses 155, CH-1066 Epalinges, Switzerland
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90
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Perea-Gomez A, Vella FDJ, Shawlot W, Oulad-Abdelghani M, Chazaud C, Meno C, Pfister V, Chen L, Robertson E, Hamada H, Behringer RR, Ang SL. Nodal antagonists in the anterior visceral endoderm prevent the formation of multiple primitive streaks. Dev Cell 2002; 3:745-56. [PMID: 12431380 DOI: 10.1016/s1534-5807(02)00321-0] [Citation(s) in RCA: 275] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The anterior visceral endoderm plays a pivotal role in establishing anterior-posterior polarity of the mouse embryo, but the molecular nature of the signals required remains to be determined. Here, we demonstrate that Cerberus-like(-/-);Lefty1(-/-) compound mutants can develop a primitive streak ectopically in the embryo. This defect is not rescued in chimeras containing wild-type embryonic, and Cerberus-like(-/-);Lefty1(-/-) extraembryonic, cells but is rescued in Cerberus-like(-/-); Lefty1(-/-) embryos after removal of one copy of the Nodal gene. Our findings provide support for a model whereby Cerberus-like and Lefty1 in the anterior visceral endoderm restrict primitive streak formation to the posterior end of mouse embryos by antagonizing Nodal signaling. Both antagonists are also required for proper patterning of the primitive streak.
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Affiliation(s)
- Aitana Perea-Gomez
- IGBMC/CNRS/INSERM, Université Louis Pasteur, 67404 Illkirch cedex, CU de, Strasbourg, France
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91
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Stern CD. Induction and initial patterning of the nervous system - the chick embryo enters the scene. Curr Opin Genet Dev 2002; 12:447-51. [PMID: 12100891 DOI: 10.1016/s0959-437x(02)00324-6] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Until recently, almost everything known about the molecular controls of early neural development came from studies in amphibians. It is now possible to misexpress factors in chick embryos at relatively late stages in development, allowing careful dissection of the timing of cell interactions. This is starting to contribute significantly to our understanding of neural induction and early patterning.
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Affiliation(s)
- Claudio D Stern
- Department of Anatomy & Developmental Biology, University College London, UK.
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92
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Hallonet M, Kaestner KH, Martin-Parras L, Sasaki H, Betz UAK, Ang SL. Maintenance of the specification of the anterior definitive endoderm and forebrain depends on the axial mesendoderm: a study using HNF3beta/Foxa2 conditional mutants. Dev Biol 2002; 243:20-33. [PMID: 11846474 DOI: 10.1006/dbio.2001.0536] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
In mouse embryo, the early induction of the head region depends on signals from the anterior visceral endoderm (AVE) and the anterior primitive streak. Subsequently, node derivatives, including anterior definitive endoderm and axial mesendoderm, are thought to play a role in the maintenance and elaboration of anterior neural character. Foxa2 encodes a winged-helix transcription factor expressed in signaling centers required for head development, including the AVE, anterior primitive streak, anterior definitive endoderm, and axial mesendoderm. To address Foxa2 function during formation of the head, we used conditional mutants in which Foxa2 function is preserved in extraembryonic tissues during early embryonic stages and inactivated in embryonic tissues after the onset of gastrulation. In Foxa2 conditional mutants, the anterior neural plate and anterior definitive endoderm were initially specified. In contrast, the axial mesendoderm failed to differentiate. At later stages, specification of the anterior neural plate and anterior definitive endoderm was shown to be labile. As a result, head truncations were observed in Foxa2 conditional mutants. Our results therefore indicate that anterior definitive endoderm alone is not sufficient to maintain anterior head specification and that an interaction between the axial mesendoderm and the anterior definitive endoderm is required for proper specification of the endoderm. Foxa2 therefore plays an integral role in the formation of axial mesendoderm, which is required to maintain the specification of the forebrain and the anterior definitive endoderm.
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Affiliation(s)
- Marc Hallonet
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/Université Louis Pasteur, C.U. de Strasbourg, Illkirch, France
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93
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Tian E, Kimura C, Takeda N, Aizawa S, Matsuo I. Otx2 is required to respond to signals from anterior neural ridge for forebrain specification. Dev Biol 2002; 242:204-23. [PMID: 11820816 DOI: 10.1006/dbio.2001.0531] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Previous analysis employing chimeric and transgenic rescue experiments has suggested that Otx2 is required in the neuroectoderm for development of the forebrain region. In order to elucidate the precise role of Otx2 in forebrain development, we attempted to generate an allelic series of Otx2 mutations by Flp- and Cre-mediated recombination for the production of conditional knock-out mice. Unexpectedly, the neo-cassette insertion created a hypomorphic Otx2 allele; consequently, the phenotype of compound mutant embryos carrying both a hypomorphic and a null allele (Otx2(frt-neo/-)) was analyzed. Otx2(frt-neo/-) mutant mice died at birth, displaying rostral head malformations. Molecular marker analysis demonstrated that Otx2(frt-neo/-) mutant embryos appeared to undergo anterior-posterior axis generation and induction of anterior neuroectoderm normally; however, these mutants subsequently failed to correctly specify the forebrain region. As the rostral margin of the neural plate, termed the anterior neural ridge (ANR), plays crucial roles with respect to neural plate specification, we examined expression of molecular markers for the ANR and the neural plate; moreover, neural plate explant studies were performed. Analyses revealed that telencephalic gene expression did not occur in mutant embryos due to defects of the neural plate; however, the mutant ANR bore normal induction activity on gene expression. These results further suggest that Otx2 dosage may be crucial in the neural plate with respect to response to inductive signals primarily from the ANR for forebrain specification.
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Affiliation(s)
- E Tian
- Department of Morphogenesis, Kumamoto University, Honjo 2-2-1, Kumamoto, 860-0811, Japan
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94
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Abstract
Otx2 is a member of a highly conserved family of homeodomain-containing transcription factors that function in early brain development. Recent studies have identified a significant number of target genes downstream of Otx2, allowing us to address the question of how it fulfils its diverse developmental roles. Interestingly, many of these target genes are not transcription factors or signaling molecules, and they probably have no direct affect on gene expression. Furthermore, there is evidence that Otx2 coordinates the activity of unrelated genes that have overlapping functions, and that it does so directly without intermediate transcriptional or signaling activity.
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Affiliation(s)
- E Boncinelli
- Molecular Biology of Development, DIBIT, Instituto Scientifico H San Raffaele, via Olgettina, 58, 20132, Milan, Italy
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95
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Abstract
Cell-cell communication is critical during embryogenesis for organizing the vertebrate body plan. Members of the Wnt family of secreted signaling molecules possess axis-inducing and posteriorizing activity when overexpressed. Wnt signals are modulated extracellularly by a diverse group of secreted Wnt antagonists and cofactors. Recent work has revealed that inhibition of posteriorly localized Wnt signaling by anteriorly localized Wnt antagonists is critical for inducing the anterior structures, forebrain and heart, from neural ectoderm and mesoderm, respectively. This review centers on the role that Wnts and Wnt antagonists play in the patterning of the vertebrate anterior-posterior axis.
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Affiliation(s)
- T P Yamaguchi
- Cancer and Developmental Biology Laboratory, National Cancer Institute-Frederick, Frederick, MD 21702, USA.
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96
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Mukhopadhyay M, Shtrom S, Rodriguez-Esteban C, Chen L, Tsukui T, Gomer L, Dorward DW, Glinka A, Grinberg A, Huang SP, Niehrs C, Izpisúa Belmonte JC, Westphal H. Dickkopf1 is required for embryonic head induction and limb morphogenesis in the mouse. Dev Cell 2001; 1:423-34. [PMID: 11702953 DOI: 10.1016/s1534-5807(01)00041-7] [Citation(s) in RCA: 484] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Dickkopf1 (Dkk1) is a secreted protein that acts as a Wnt inhibitor and, together with BMP inhibitors, is able to induce the formation of ectopic heads in Xenopus. Here, we show that Dkk1 null mutant embryos lack head structures anterior of the midbrain. Analysis of chimeric embryos implicates the requirement of Dkk1 in anterior axial mesendoderm but not in anterior visceral endoderm for head induction. In addition, mutant embryos show duplications and fusions of limb digits. Characterization of the limb phenotype strongly suggests a role for Dkk1 both in cell proliferation and in programmed cell death. Our data provide direct genetic evidence for the requirement of secreted Wnt antagonists during embryonic patterning and implicate Dkk1 as an essential inducer during anterior specification as well as a regulator during distal limb patterning.
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Affiliation(s)
- M Mukhopadhyay
- Laboratory of Mammalian Genes and Development, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
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97
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Lu CC, Brennan J, Robertson EJ. From fertilization to gastrulation: axis formation in the mouse embryo. Curr Opin Genet Dev 2001; 11:384-92. [PMID: 11448624 DOI: 10.1016/s0959-437x(00)00208-2] [Citation(s) in RCA: 185] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Although much remains unknown about how the embryonic axis is laid down in the mouse, it is now clear that reciprocal interactions between the extraembryonic and embryonic lineages establish and reinforce patterning of the embryo. At early post-implantation stages, the extraembryonic ectoderm appears to impart proximal-posterior identity to the adjacent proximal epiblast, whereas the distal visceral endoderm signals to the underlying epiblast to restrict posterior identity as it moves anteriorward. At gastrulation, the visceral endoderm is necessary for specifying anterior primitive streak derivatives, which, in turn, pattern the anterior epiblast. Polarity of these extraembryonic tissues can be traced back to the blastocyst stage, where asymmetry has been linked to the point of sperm entry at fertilization.
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Affiliation(s)
- C C Lu
- 16 Divinity Avenue, Department of Molecular and Cellular Biology, Harvard University, 02138, Cambridge, Massachusetts, USA.
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