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Koo B, Lee KH, Ming GL, Yoon KJ, Song H. Setting the clock of neural progenitor cells during mammalian corticogenesis. Semin Cell Dev Biol 2023; 142:43-53. [PMID: 35644876 PMCID: PMC9699901 DOI: 10.1016/j.semcdb.2022.05.013] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2022] [Revised: 05/06/2022] [Accepted: 05/16/2022] [Indexed: 10/18/2022]
Abstract
Radial glial cells (RGCs) as primary neural stem cells in the developing mammalian cortex give rise to diverse types of neurons and glial cells according to sophisticated developmental programs with remarkable spatiotemporal precision. Recent studies suggest that regulation of the temporal competence of RGCs is a key mechanism for the highly conserved and predictable development of the cerebral cortex. Various types of epigenetic regulations, such as DNA methylation, histone modifications, and 3D chromatin architecture, play a key role in shaping the gene expression pattern of RGCs. In addition, epitranscriptomic modifications regulate temporal pre-patterning of RGCs by affecting the turnover rate and function of cell-type-specific transcripts. In this review, we summarize epigenetic and epitranscriptomic regulatory mechanisms that control the temporal competence of RGCs during mammalian corticogenesis. Furthermore, we discuss various developmental elements that also dynamically regulate the temporal competence of RGCs, including biochemical reaction speed, local environmental changes, and subcellular organelle remodeling. Finally, we discuss the underlying mechanisms that regulate the interspecies developmental tempo contributing to human-specific features of brain development.
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Affiliation(s)
- Bonsang Koo
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Ki-Heon Lee
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Guo-Li Ming
- Department of Neuroscience and Mahoney Institute for Neurosciences, Perelman School for Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Institute for Regenerative Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Department of Psychiatry, Perelman School for Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Ki-Jun Yoon
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea.
| | - Hongjun Song
- Department of Neuroscience and Mahoney Institute for Neurosciences, Perelman School for Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Department of Cell and Developmental Biology, Perelman School for Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Institute for Regenerative Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; The Epigenetics Institute, Perelman School for Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
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2
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Kim EJY, Sorokin L, Hiiragi T. ECM-integrin signalling instructs cellular position-sensing to pattern the early mouse embryo. Development 2021; 149:273721. [PMID: 34908109 PMCID: PMC8881741 DOI: 10.1242/dev.200140] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2021] [Accepted: 12/03/2021] [Indexed: 11/20/2022]
Abstract
Development entails patterned emergence of diverse cell types within the embryo. In mammals, cells positioned inside the embryo give rise to the inner cell mass (ICM), which eventually forms the embryo itself. Yet, the molecular basis of how these cells recognise their ‘inside’ position to instruct their fate is unknown. Here, we show that provision of extracellular matrix (ECM) to isolated embryonic cells induces ICM specification and alters the subsequent spatial arrangement between epiblast (EPI) and primitive endoderm (PrE) cells that emerge within the ICM. Notably, this effect is dependent on integrin β1 activity and involves apical-to-basal conversion of cell polarity. We demonstrate that ECM-integrin activity is sufficient for ‘inside’ positional signalling and is required for correct EPI/PrE patterning. Thus, our findings highlight the significance of ECM-integrin adhesion in enabling position sensing by cells to achieve tissue patterning. Summary: The importance of patterned cell-extracellular matrix (ECM) interactions in early mouse development: ECM signals can modulate both cell fate and the relative spatial arrangement between cells.
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Affiliation(s)
- Esther Jeong Yoon Kim
- European Molecular Biology Laboratory (EMBL), Heidelberg, Germany.,Collaboration for joint PhD degree between EMBL and Heidelberg University, Faculty of Biosciences, Universität Heidelberg, Heidelberg, Germany
| | - Lydia Sorokin
- Institute of Physiological Chemistry and Pathobiochemistry and Cells in Motion Interfaculty Centre (CiMIC), University of Muenster, Germany
| | - Takashi Hiiragi
- European Molecular Biology Laboratory (EMBL), Heidelberg, Germany.,Institute for the Advanced Study of Human Biology (WPI-ASHBi), Kyoto University, Kyoto, Japan
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3
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Shiau F, Ruzycki PA, Clark BS. A single-cell guide to retinal development: Cell fate decisions of multipotent retinal progenitors in scRNA-seq. Dev Biol 2021; 478:41-58. [PMID: 34146533 PMCID: PMC8386138 DOI: 10.1016/j.ydbio.2021.06.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2021] [Revised: 06/07/2021] [Accepted: 06/08/2021] [Indexed: 12/20/2022]
Abstract
Recent advances in high throughput single-cell RNA sequencing (scRNA-seq) technology have enabled the simultaneous transcriptomic profiling of thousands of individual cells in a single experiment. To investigate the intrinsic process of retinal development, researchers have leveraged this technology to quantify gene expression in retinal cells across development, in multiple species, and from numerous important models of human disease. In this review, we summarize recent applications of scRNA-seq and discuss how these datasets have complemented and advanced our understanding of retinal progenitor cell competence, cell fate specification, and differentiation. Finally, we also highlight the outstanding questions in the field that advances in single-cell data generation and analysis will soon be able to answer.
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Affiliation(s)
- Fion Shiau
- John F Hardesty, MD Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO, USA
| | - Philip A Ruzycki
- John F Hardesty, MD Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO, USA
| | - Brian S Clark
- John F Hardesty, MD Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO, USA; Department of Developmental Biology, Washington University School of Medicine, St. Louis, MO, USA.
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4
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Rajan SG, Nacke LM, Dhingra JS, Saxena A. Notch signaling mediates olfactory multiciliated cell specification. Cells Dev 2021; 168:203715. [PMID: 34217886 DOI: 10.1016/j.cdev.2021.203715] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Revised: 06/12/2021] [Accepted: 06/21/2021] [Indexed: 11/17/2022]
Abstract
Epithelial multiciliated cells (MCCs) use motile cilia to direct external fluid flow, the disruption of which is associated with human diseases in a broad array of organs such as those in the respiratory, reproductive, and renal systems. While many of the signaling pathways that regulate MCC formation in these organ systems have been identified, similar characterization of MCC differentiation in the developing olfactory system has been lacking. Here, using live cell tracking, targeted cell ablation, and temporally-specific inhibition of the Notch signaling pathway, we identify the earliest time window of zebrafish olfactory MCC (OMCC) differentiation and demonstrate these cells' derivation from peridermal cells. We also describe regionally segregated Notch signaling across time points of rapid OMCC differentiation and show that Notch signaling downregulation yields an increase in OMCCs, suggesting that OMCC fate is normally repressed in a region-specific manner during olfactory development. Finally, we describe Notch signaling's regulation of the differentiation/ciliogenesis-associated genes foxj1a and foxj1b. Taken together, these findings provide new insights into the origins and developmental programming of OMCCs in vivo.
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Affiliation(s)
- Sriivatsan G Rajan
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Lynne M Nacke
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Jagjot S Dhingra
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Ankur Saxena
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA.
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5
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Bardot ES, Hadjantonakis AK. Mouse gastrulation: Coordination of tissue patterning, specification and diversification of cell fate. Mech Dev 2020; 163:103617. [PMID: 32473204 PMCID: PMC7534585 DOI: 10.1016/j.mod.2020.103617] [Citation(s) in RCA: 54] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2020] [Revised: 05/18/2020] [Accepted: 05/22/2020] [Indexed: 12/22/2022]
Abstract
During mouse embryonic development a mass of pluripotent epiblast tissue is transformed during gastrulation to generate the three definitive germ layers: endoderm, mesoderm, and ectoderm. During gastrulation, a spatiotemporally controlled sequence of events results in the generation of organ progenitors and positions them in a stereotypical fashion throughout the embryo. Key to the correct specification and differentiation of these cell fates is the establishment of an axial coordinate system along with the integration of multiple signals by individual epiblast cells to produce distinct outcomes. These signaling domains evolve as the anterior-posterior axis is established and the embryo grows in size. Gastrulation is initiated at the posteriorly positioned primitive streak, from which nascent mesoderm and endoderm progenitors ingress and begin to diversify. Advances in technology have facilitated the elaboration of landmark findings that originally described the epiblast fate map and signaling pathways required to execute those fates. Here we will discuss the current state of the field and reflect on how our understanding has shifted in recent years.
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Affiliation(s)
- Evan S Bardot
- Developmental Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, NY 10065, USA.
| | - Anna-Katerina Hadjantonakis
- Developmental Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, NY 10065, USA.
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6
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Wang S, Ochoa SD, Khaliullin RN, Gerson-Gurwitz A, Hendel JM, Zhao Z, Biggs R, Chisholm AD, Desai A, Oegema K, Green RA. A high-content imaging approach to profile C. elegans embryonic development. Development 2019; 146:dev174029. [PMID: 30890570 PMCID: PMC6467471 DOI: 10.1242/dev.174029] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2018] [Accepted: 03/11/2019] [Indexed: 11/20/2022]
Abstract
The Caenorhabditis elegans embryo is an important model for analyzing mechanisms of cell fate specification and tissue morphogenesis. Sophisticated lineage-tracing approaches for analyzing embryogenesis have been developed but are labor intensive and do not naturally integrate morphogenetic readouts. To enable the rapid classification of developmental phenotypes, we developed a high-content method that employs two custom strains: a Germ Layer strain that expresses nuclear markers in the ectoderm, mesoderm and endoderm/pharynx; and a Morphogenesis strain that expresses markers labeling epidermal cell junctions and the neuronal cell surface. We describe a procedure that allows simultaneous live imaging of development in 80-100 embryos and provide a custom program that generates cropped, oriented image stacks of individual embryos to facilitate analysis. We demonstrate the utility of our method by perturbing 40 previously characterized developmental genes in variants of the two strains containing RNAi-sensitizing mutations. The resulting datasets yielded distinct, reproducible signature phenotypes for a broad spectrum of genes that are involved in cell fate specification and morphogenesis. In addition, our analysis provides new in vivo evidence for MBK-2 function in mesoderm fate specification and LET-381 function in elongation.
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Affiliation(s)
- Shaohe Wang
- Ludwig Institute for Cancer Research, Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA 92093, USA
- Biomedical Sciences Graduate Program, University of California, San Diego, La Jolla, CA 92093, USA
| | - Stacy D Ochoa
- Ludwig Institute for Cancer Research, Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA 92093, USA
| | - Renat N Khaliullin
- Ludwig Institute for Cancer Research, Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA 92093, USA
| | - Adina Gerson-Gurwitz
- Ludwig Institute for Cancer Research, Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA 92093, USA
| | - Jeffrey M Hendel
- Ludwig Institute for Cancer Research, Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA 92093, USA
| | - Zhiling Zhao
- Ludwig Institute for Cancer Research, Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA 92093, USA
| | - Ronald Biggs
- Ludwig Institute for Cancer Research, Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA 92093, USA
| | - Andrew D Chisholm
- Section of Cell and Developmental Biology, Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA
| | - Arshad Desai
- Ludwig Institute for Cancer Research, Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA 92093, USA
| | - Karen Oegema
- Ludwig Institute for Cancer Research, Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA 92093, USA
| | - Rebecca A Green
- Ludwig Institute for Cancer Research, Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA 92093, USA
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7
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Guo Q, Li JYH. Defining developmental diversification of diencephalon neurons through single cell gene expression profiling. Development 2019; 146:dev.174284. [PMID: 30872278 DOI: 10.1242/dev.174284] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2018] [Accepted: 03/07/2019] [Indexed: 12/31/2022]
Abstract
The embryonic diencephalon forms integration centers and relay stations in the forebrain. Anecdotal expression studies suggest that the diencephalon contains multiple developmental compartments and subdivisions. Here, we utilized single cell RNA sequencing to profile transcriptomes of dissociated cells from the diencephalon of E12.5 mouse embryos. We identified the divergence of different progenitors, intermediate progenitors, and emerging neurons. By mapping the identified cell groups to their spatial origins, we characterized the molecular features of cell types and cell states arising from various diencephalic domains. Furthermore, we reconstructed the developmental trajectory of distinct cell lineages, and thereby identified the genetic cascades and gene regulatory networks underlying the progression of the cell cycle, neurogenesis and cellular diversification. The analysis provides new insights into the molecular mechanisms underlying the amplification of intermediate progenitor cells in the thalamus. The single cell-resolved trajectories not only confirm a close relationship between the rostral thalamus and prethalamus, but also uncover an unexpected close relationship between the caudal thalamus, epithalamus and rostral pretectum. Our data provide a useful resource for systematic studies of cell heterogeneity and differentiation kinetics within the diencephalon.
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Affiliation(s)
- Qiuxia Guo
- Department of Genetics and Genome Sciences, University of Connecticut School of Medicine, 263 Farmington Avenue, Farmington, CT 06030-6403, USA
| | - James Y H Li
- Department of Genetics and Genome Sciences, University of Connecticut School of Medicine, 263 Farmington Avenue, Farmington, CT 06030-6403, USA .,Institute for Systems Genomics, University of Connecticut, 400 Farmington Avenue, Farmington, CT 06030-6403, USA
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8
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Saadin A, Starz-Gaiano M. Cytokine exocytosis and JAK/STAT activation in the Drosophila ovary requires the vesicle trafficking regulator α-Snap. J Cell Sci 2018; 131:jcs217638. [PMID: 30404830 PMCID: PMC6288073 DOI: 10.1242/jcs.217638] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2018] [Accepted: 10/11/2018] [Indexed: 01/03/2023] Open
Abstract
How vesicle trafficking components actively contribute to regulation of paracrine signaling is unclear. We genetically uncovered a requirement for α-soluble NSF attachment protein (α-Snap) in the activation of the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway during Drosophila egg development. α-Snap, a well-conserved vesicle trafficking regulator, mediates association of N-ethylmaleimide-sensitive factor (NSF) and SNAREs to promote vesicle fusion. Depletion of α-Snap or the SNARE family member Syntaxin1A in epithelia blocks polar cells maintenance and prevents specification of motile border cells. Blocking apoptosis rescues polar cell maintenance in α-Snap-depleted egg chambers, indicating that the lack of border cells in mutants is due to impaired signaling. Genetic experiments implicate α-Snap and NSF in secretion of a STAT-activating cytokine. Live imaging suggests that changes in intracellular Ca2+ are linked to this event. Our data suggest a cell-type specific requirement for particular vesicle trafficking components in regulated exocytosis during development. Given the central role for STAT signaling in immunity, this work may shed light on regulation of cytokine release in humans.
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Affiliation(s)
- Afsoon Saadin
- Department of Biological Sciences, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA
| | - Michelle Starz-Gaiano
- Department of Biological Sciences, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA
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9
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Jin K, Xiang M. Transcription factor Ptf1a in development, diseases and reprogramming. Cell Mol Life Sci 2018; 76:921-940. [PMID: 30470852 DOI: 10.1007/s00018-018-2972-z] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2018] [Revised: 11/13/2018] [Accepted: 11/19/2018] [Indexed: 12/12/2022]
Abstract
The transcription factor Ptf1a is a crucial helix-loop-helix (bHLH) protein selectively expressed in the pancreas, retina, spinal cord, brain, and enteric nervous system. Ptf1a is preferably assembled into a transcription trimeric complex PTF1 with an E protein and Rbpj (or Rbpjl). In pancreatic development, Ptf1a is indispensable in controlling the expansion of multipotent progenitor cells as well as the specification and maintenance of the acinar cells. In neural tissues, Ptf1a is transiently expressed in the post-mitotic cells and specifies the inhibitory neuronal cell fates, mostly mediated by downstream genes such as Tfap2a/b and Prdm13. Mutations in the coding and non-coding regulatory sequences resulting in Ptf1a gain- or loss-of-function are associated with genetic diseases such as pancreatic and cerebellar agenesis in the rodent and human. Surprisingly, Ptf1a alone is sufficient to reprogram mouse or human fibroblasts into tripotential neural stem cells. Its pleiotropic functions in many biological processes remain to be deciphered in the future.
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Affiliation(s)
- Kangxin Jin
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, 510060, China.
| | - Mengqing Xiang
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, 510060, China.
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10
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Bernabeu-Zornoza A, Coronel R, Palmer C, Calero M, Martínez-Serrano A, Cano E, Zambrano A, Liste I. Aβ42 Peptide Promotes Proliferation and Gliogenesis in Human Neural Stem Cells. Mol Neurobiol 2019; 56:4023-36. [PMID: 30259399 DOI: 10.1007/s12035-018-1355-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2018] [Accepted: 09/17/2018] [Indexed: 10/28/2022]
Abstract
Amyloid-β 42 [Aβ1-42 (Aβ42)] is one of the main Aβ peptide isoforms found in amyloid plaques of brains with Alzheimer's disease (AD). Although Aβ42 is associated with neurotoxicity, it might mediate several normal physiological processes during embryonic brain development and in the adult brain. However, due to the controversy that exists in the field, relatively little is known about its physiological function. In the present work, we have analyzed the effects of different concentrations of monomeric Aβ42 on cell death, proliferation, and cell fate specification of human neural stem cells (hNSCs), specifically the hNS1 cell line, undergoing differentiation. Our results demonstrate that at higher concentrations (1 μM), Aβ42 increases apoptotic cell death and DNA damage, indicating that prolonged exposure of hNS1 cells to higher concentrations of Aβ42 is neurotoxic. However, at lower concentrations, Aβ42 significantly promotes cell proliferation and glial cell specification of hNS1 cells by increasing the pool of proliferating glial precursors, without affecting neuronal differentiation, in a concentration-dependent manner. At the molecular level, these effects could be mediated, at least in part, by GSK3β, whose expression is increased by treatment with Aβ42 and whose inhibition prevents the glial specification induced by Aβ42. Since the cellular and molecular effects are known to appear decades before the first clinical symptoms, these types of studies are important in discovering the underlying pathophysiological processes involved in the development of AD. This knowledge could then be used in diagnosing the disease at early stages and be applied to the development of new treatment options.
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11
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Webber JL, Zhang J, Massey A, Sanchez-Luege N, Rebay I. Collaborative repressive action of the antagonistic ETS transcription factors Pointed and Yan fine-tunes gene expression to confer robustness in Drosophila. Development 2018; 145:dev.165985. [PMID: 29848501 DOI: 10.1242/dev.165985] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Accepted: 05/17/2018] [Indexed: 01/29/2023]
Abstract
The acquisition of cellular identity during development depends on precise spatiotemporal regulation of gene expression, with combinatorial interactions between transcription factors, accessory proteins and the basal transcription machinery together translating complex signaling inputs into appropriate gene expression outputs. The opposing repressive and activating inputs of the Drosophila ETS family transcription factors Yan and Pointed orchestrate numerous cell fate transitions downstream of receptor tyrosine kinase signaling, providing one of the premier systems for studying this process. Current models describe the differentiative transition as a switch from Yan-mediated repression to Pointed-mediated activation of common target genes. We describe here a new layer of regulation whereby Yan and Pointed co-occupy regulatory elements to repress gene expression in a coordinated manner, with Pointed being unexpectedly required for the genome-wide occupancy of both Yan and the co-repressor Groucho. Using even skipped as a test-case, synergistic genetic interactions between Pointed, Groucho, Yan and components of the RNA polymerase II pausing machinery suggest that Pointed integrates multiple scales of repressive regulation to confer robustness. We speculate that this mechanism may be used broadly to fine-tune the expression of many genes crucial for development.
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Affiliation(s)
- Jemma L Webber
- Ben May Department for Cancer Research, University of Chicago, Chicago, IL 60637, USA
| | - Jie Zhang
- Ben May Department for Cancer Research, University of Chicago, Chicago, IL 60637, USA
| | - Alex Massey
- Ben May Department for Cancer Research, University of Chicago, Chicago, IL 60637, USA
| | - Nicelio Sanchez-Luege
- Ben May Department for Cancer Research, University of Chicago, Chicago, IL 60637, USA
| | - Ilaria Rebay
- Ben May Department for Cancer Research, University of Chicago, Chicago, IL 60637, USA
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12
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Peng X, Sun MX. The suspensor as a model system to study the mechanism of cell fate specification during early embryogenesis. Plant Reprod 2018; 31:59-65. [PMID: 29473100 PMCID: PMC5845063 DOI: 10.1007/s00497-018-0326-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2017] [Accepted: 02/14/2018] [Indexed: 05/24/2023]
Abstract
The advances in the suspensor. During early embryogenesis, the proembryo consists of two domains, the embryo proper and the suspensor. Unlike the embryo proper, which has been investigated extensively, research on the suspensor has been limited in past decades. Recent studies have revealed that the suspensor plays an important role in early embryogenesis and the process of suspensor formation and degeneration may provide a unique model for studies on cell division pattern, cell fate determination, and cell death. In this review, we briefly summarize the advances in research on the suspensor, which provide new insight in our understanding of the mechanism of early embryogenesis and show great potential for a unique model for future investigations.
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Affiliation(s)
- Xiongbo Peng
- State Key Laboratory of Hybrid Rice, College of Life Science, Wuhan University, Wuhan, 430072, China
| | - Meng-Xiang Sun
- State Key Laboratory of Hybrid Rice, College of Life Science, Wuhan University, Wuhan, 430072, China.
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13
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von Dassow G, Maslakova SA. The trochoblasts in the pilidium larva break an ancient spiralian constraint to enable continuous larval growth and maximally indirect development. EvoDevo 2017; 8:19. [PMID: 29090082 PMCID: PMC5655816 DOI: 10.1186/s13227-017-0079-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2017] [Accepted: 10/04/2017] [Indexed: 11/24/2022] Open
Abstract
BACKGROUND Nemertean embryos undergo equal spiral cleavage, and prior fate-mapping studies showed that some also exhibit key aspects of spiralian lineage-based fate specification, including specification of the primary trochoblasts, which differentiate early as the core of the prototroch of the spiralian trochophore larva. Yet it remains unclear how the nemertean pilidium larva, a long-lived planktotroph that grows substantially as it builds a juvenile body from isolated rudiments, develops within the constraints of spiral cleavage. RESULTS We marked single cells in embryos of the pilidiophoran Maculaura alaskensis to show that primary, secondary, and accessory trochoblasts, cells that would make the prototroch in conventional spiralian trochophores (1q2, 1q12, and some descendants of 2q), fully account for the pilidium's primary ciliary band, but without undergoing early cleavage arrest. Instead, the primary ciliary band consists of many small, albeit terminally differentiated, cells. The trochoblasts also give rise to niches of indefinitely proliferative cells ("axils") that sustain continuous growth of the larval body, including new ciliated band. Several of the imaginal rudiments that form the juvenile body arise from the axils: in particular, we show that cephalic imaginal disks originate from 1a2 and 1b12 and that trunk imaginal disks likely originate from 2d. CONCLUSIONS The pilidium exhibits a familiar relation between identified blastomeres and the primary ciliated band, but the manner in which these cells form this organ differs fundamentally from the way equivalent cells construct the trochophore's prototroch. Also, the establishment, by some progeny of the putative trochoblasts, of indeterminate stem cell populations that give rise to juvenile rudiments, as opposed to an early cleavage arrest, implies a radical alteration in their developmental program. This transition may have been essential to the evolution of a maximally indirect developing larval form-the pilidium-among nemerteans.
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Affiliation(s)
- George von Dassow
- Oregon Institute of Marine Biology, University of Oregon, P.O. Box 5389, Charleston, OR 97420 USA
| | - Svetlana A. Maslakova
- Oregon Institute of Marine Biology, University of Oregon, P.O. Box 5389, Charleston, OR 97420 USA
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14
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Shen Q, Shi H, Tian C, Ghai V, Liu J. The C. elegans Spalt-like protein SEM-4 functions through the SoxC transcription factor SEM-2 to promote a proliferative blast cell fate in the postembryonic mesoderm. Dev Biol 2017; 429:335-342. [PMID: 28614700 DOI: 10.1016/j.ydbio.2017.06.011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2017] [Revised: 06/09/2017] [Accepted: 06/09/2017] [Indexed: 11/29/2022]
Abstract
Proper development of a multicellular organism relies on well-coordinated regulation of cell fate specification, cell proliferation and cell differentiation. The C. elegans postembryonic mesoderm provides a useful system for uncovering factors involved in these processes and for further dissecting their regulatory relationships. The single Spalt-like zinc finger containing protein SEM-4/SALL is known to be involved in specifying the proliferative sex myoblast (SM) fate. We have found that SEM-4/SALL is sufficient to promote the SM fate and that it does so in a cell autonomous manner. We further showed that SEM-4/SALL acts through the SoxC transcription factor SEM-2 to promote the SM fate. SEM-2 is known to promote the SM fate by inhibiting the expression of two BWM-specifying transcription factors. In light of recent findings in mammals showing that Sall4, one of the mammalian homologs of SEM-4, contributes to pluripotency regulation by inhibiting differentiation, our work suggests that the function of SEM-4/SALL proteins in regulating pluripotency versus differentiation appears to be evolutionarily conserved.
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Affiliation(s)
- Qinfang Shen
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, United States
| | - Herong Shi
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, United States
| | - Chenxi Tian
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, United States
| | - Vikas Ghai
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, United States
| | - Jun Liu
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, United States.
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15
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Grebbin BM, Hau AC, Groß A, Anders-Maurer M, Schramm J, Koss M, Wille C, Mittelbronn M, Selleri L, Schulte D. Pbx1 is required for adult subventricular zone neurogenesis. Development 2016; 143:2281-91. [PMID: 27226325 DOI: 10.1242/dev.128033] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2015] [Accepted: 05/15/2016] [Indexed: 12/22/2022]
Abstract
TALE-homeodomain proteins function as components of heteromeric complexes that contain one member each of the PBC and MEIS/PREP subclasses. We recently showed that MEIS2 cooperates with the neurogenic transcription factor PAX6 in the control of adult subventricular zone (SVZ) neurogenesis in rodents. Expression of the PBC protein PBX1 in the SVZ has been reported, but its functional role(s) has not been investigated. Using a genetic loss-of-function mouse model, we now show that Pbx1 is an early regulator of SVZ neurogenesis. Targeted deletion of Pbx1 by retroviral transduction of Cre recombinase into Pbx2-deficient SVZ stem and progenitor cells carrying floxed alleles of Pbx1 significantly reduced the production of neurons and increased the generation of oligodendrocytes. Loss of Pbx1 expression in neuronally committed neuroblasts in the rostral migratory stream in a Pbx2 null background, by contrast, severely compromised cell survival. By chromatin immunoprecipitation from endogenous tissues or isolated cells, we further detected PBX1 binding to known regulatory regions of the neuron-specific genes Dcx and Th days or even weeks before the respective genes are expressed during the normal program of SVZ neurogenesis, suggesting that PBX1 might act as a priming factor to mark these genes for subsequent activation. Collectively, our results establish that PBX1 regulates adult neural cell fate determination in a manner beyond that of its heterodimerization partner MEIS2.
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Affiliation(s)
- Britta Moyo Grebbin
- Institute of Neurology (Edinger Institute), J. W. Goethe University Medical School, German Cancer Consortium (DKTK), Heinrich-Hoffmann Str. 7, Frankfurt D-60528, Germany
| | - Ann-Christin Hau
- Institute of Neurology (Edinger Institute), J. W. Goethe University Medical School, German Cancer Consortium (DKTK), Heinrich-Hoffmann Str. 7, Frankfurt D-60528, Germany
| | - Anja Groß
- Institute of Neurology (Edinger Institute), J. W. Goethe University Medical School, German Cancer Consortium (DKTK), Heinrich-Hoffmann Str. 7, Frankfurt D-60528, Germany
| | - Marie Anders-Maurer
- Institute of Neurology (Edinger Institute), J. W. Goethe University Medical School, German Cancer Consortium (DKTK), Heinrich-Hoffmann Str. 7, Frankfurt D-60528, Germany
| | - Jasmine Schramm
- Institute of Neurology (Edinger Institute), J. W. Goethe University Medical School, German Cancer Consortium (DKTK), Heinrich-Hoffmann Str. 7, Frankfurt D-60528, Germany
| | - Matthew Koss
- Department of Cell and Developmental Biology, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10065, USA
| | - Christoph Wille
- Institute of Neurology (Edinger Institute), J. W. Goethe University Medical School, German Cancer Consortium (DKTK), Heinrich-Hoffmann Str. 7, Frankfurt D-60528, Germany
| | - Michel Mittelbronn
- Institute of Neurology (Edinger Institute), J. W. Goethe University Medical School, German Cancer Consortium (DKTK), Heinrich-Hoffmann Str. 7, Frankfurt D-60528, Germany
| | - Licia Selleri
- Department of Cell and Developmental Biology, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10065, USA Program in Craniofacial Biology, Institute of Human Genetics, Eli and Edythe Broad Center of Regeneration Medicine & Stem Cell Research, Departments of Orofacial Sciences and Anatomy, University of California, San Francisco, 513 Parnassus Avenue, HSW 710, San Francisco, CA 94143, USA
| | - Dorothea Schulte
- Institute of Neurology (Edinger Institute), J. W. Goethe University Medical School, German Cancer Consortium (DKTK), Heinrich-Hoffmann Str. 7, Frankfurt D-60528, Germany
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16
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Abstract
Cell fate specification is a critical process to generate cells with a wide range of characteristics from stem and progenitor cells. Emerging evidence demonstrates that the orphan nuclear receptor COUP-TFII serves as a key regulator in determining the cell identity during embryonic development. The present review summarizes our current knowledge on molecular mechanisms by which COUP-TFII employs to define the cell fates, with special emphasis on cardiovascular and renal systems. These novel insights pave the road for future studies of regenerative medicine.
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Affiliation(s)
- San-Pin Wu
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030, USA; Adrienne Helis Malvin Medical Research Foundation, New Orleans, LA 70130, USA
| | - Cheng-Tai Yu
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Sophia Y Tsai
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030, USA; Program in Developmental Biology, Baylor College of Medicine, Houston, TX 77030, USA.
| | - Ming-Jer Tsai
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030, USA; Program in Developmental Biology, Baylor College of Medicine, Houston, TX 77030, USA.
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17
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Abstract
Photoreceptors--the light-sensitive cells in the vertebrate retina--have been extremely well-characterized with regards to their biochemistry, cell biology and physiology. They therefore provide an excellent model for exploring the factors and mechanisms that drive neural progenitors into a differentiated cell fate in the nervous system. As a result, great progress in understanding the transcriptional network that controls photoreceptor specification and differentiation has been made over the last 20 years. This progress has also enabled the production of photoreceptors from pluripotent stem cells, thereby aiding the development of regenerative medical approaches to eye disease. In this Review, we outline the signaling and transcription factors that drive vertebrate photoreceptor development and discuss how these function together in gene regulatory networks to control photoreceptor cell fate specification.
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Affiliation(s)
- Joseph A Brzezinski
- Department of Ophthalmology, University of Colorado Denver, Aurora, CO 80045, USA
| | - Thomas A Reh
- Department of Biological Structure, University of Washington, Seattle, WA 98195, USA
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18
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Sasaki H. Position- and polarity-dependent Hippo signaling regulates cell fates in preimplantation mouse embryos. Semin Cell Dev Biol 2015; 47-48:80-7. [PMID: 25986053 DOI: 10.1016/j.semcdb.2015.05.003] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2015] [Revised: 05/08/2015] [Accepted: 05/08/2015] [Indexed: 11/25/2022]
Abstract
During the preimplantation stage, mouse embryos establish two cell lineages by the time of early blastocyst formation: the trophectoderm (TE) and the inner cell mass (ICM). Historical models have proposed that the establishment of these two lineages depends on the cell position within the embryo (e.g., the positional model) or cell polarization along the apicobasal axis (e.g., the polarity model). Recent findings have revealed that the Hippo signaling pathway plays a central role in the cell fate-specification process: active and inactive Hippo signaling in the inner and outer cells promote ICM and TE fates, respectively. Intercellular adhesion activates, while apicobasal polarization suppresses Hippo signaling, and a combination of these processes determines the spatially regulated activation of the Hippo pathway in 32-cell-stage embryos. Therefore, there is experimental evidence in favor of both positional and polarity models. At the molecular level, phosphorylation of the Hippo-pathway component angiomotin at adherens junctions (AJs) in the inner (apolar) cells activates the Lats protein kinase and triggers Hippo signaling. In the outer cells, however, cell polarization sequesters Amot from basolateral AJs and suppresses activation of the Hippo pathway. Other mechanisms, including asymmetric cell division and Notch signaling, also play important roles in the regulation of embryonic development. In this review, I discuss how these mechanisms cooperate with the Hippo signaling pathway during cell fate-specification processes.
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Affiliation(s)
- Hiroshi Sasaki
- Laboratory for Embryogenesis, Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan.
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19
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Kim JE, Lee WY, Kim GJ. Expression of Hr-Erf Gene during Ascidian Embryogenesis. Dev Reprod 2015; 17:389-97. [PMID: 25949155 PMCID: PMC4382941 DOI: 10.12717/dr.2013.17.4.389] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2013] [Revised: 12/09/2013] [Accepted: 12/14/2013] [Indexed: 11/23/2022]
Abstract
FGF9/16/20 signaling pathway specify the developmental fates of notochord, mesenchyme, and neural cells in ascidian embryos. Although a conserved Ras/MEK/Erk/Ets pathway is known to be involved in this signaling, the detailed mechanisms of regulation of FGF signaling pathway have remained largely elusive. In this study, we have isolated Hr-Erf, an ascidian orthologue of vertebrate Erf, to elucidate interactions of transcription factors involved in FGF signaling of the ascidian embryo. The Hr-Erf cDNA encompassed 3110 nucleotides including sequence encoded a predicted polypeptide of 760 amino acids. The polypeptide had the Ets DNA-binding domain in its N-terminal region. In adult animals, Hr-Erf mRNA was predominantly detected in muscle, and at lower levels in ganglion, gills, gonad, hepatopancreas, and stomach by quantitative real-time PCR (QPCR) method. During embryogenesis, Hr-Erf mRNA was detected from eggs to early developmental stage embryos, whereas the transcript levels were decreased after neurula stage. Similar to the QPCR results, maternal transcripts of Hr-Erf was detected in the fertilized eggs by whole-mount in situ hybridization. Maternal mRNA of Hr-Erf was gradually lost from the neurula stage. Zygotic expression of Hr-Erf started in most blastomeres at the 8-cell stage. At gastrula stage, Hr-Erf was specifically expressed in the precursor cells of brain and mesenchyme. When MEK inhibitor was treated, embryos resulted in loss of Hr-Erf expression in mesenchyme cells, and in excess of Hr-Erf in a-line neural cells. These results suggest that zygotic Hr-Erf products are involved in specification of mesenchyme and neural cells.
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Affiliation(s)
- Jung Eun Kim
- Department of Marine Molecular Biotechnology, Gangneung-Wonju National University, Gangneung 210-702, Republic of Korea
| | - Won Young Lee
- Department of Marine Molecular Biotechnology, Gangneung-Wonju National University, Gangneung 210-702, Republic of Korea
| | - Gil Jung Kim
- Department of Marine Molecular Biotechnology, Gangneung-Wonju National University, Gangneung 210-702, Republic of Korea
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20
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Cheng X, Lyons DC, Socolar JES, McClay DR. Delayed transition to new cell fates during cellular reprogramming. Dev Biol 2014; 391:147-57. [PMID: 24780626 PMCID: PMC4064802 DOI: 10.1016/j.ydbio.2014.04.015] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2013] [Revised: 04/19/2014] [Accepted: 04/21/2014] [Indexed: 01/08/2023]
Abstract
In many embryos specification toward one cell fate can be diverted to a different cell fate through a reprogramming process. Understanding how that process works will reveal insights into the developmental regulatory logic that emerged from evolution. In the sea urchin embryo, cells at gastrulation were found to reprogram and replace missing cell types after surgical dissections of the embryo. Non-skeletogenic mesoderm (NSM) cells reprogrammed to replace missing skeletogenic mesoderm cells and animal caps reprogrammed to replace all endomesoderm. In both cases evidence of reprogramming onset was first observed at the early gastrula stage, even if the cells to be replaced were removed earlier in development. Once started however, the reprogramming occurred with compressed gene expression dynamics. The NSM did not require early contact with the skeletogenic cells to reprogram, but the animal cap cells gained the ability to reprogram early in gastrulation only after extended contact with the vegetal halves prior to that time. If the entire vegetal half was removed at early gastrula, the animal caps reprogrammed and replaced the vegetal half endomesoderm. If the animal caps carried morpholinos to either hox11/13b or foxA (endomesoderm specification genes), the isolated animal caps failed to reprogram. Together these data reveal that the emergence of a reprogramming capability occurs at early gastrulation in the sea urchin embryo and requires activation of early specification components of the target tissues.
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Affiliation(s)
- Xianrui Cheng
- Program in Computational Biology and Bioinformatics, Duke University, Durham, NC 27708, USA; Duke Center for Systems Biology, Duke University, Durham, NC 27708, USA; Department of Biology, Duke University, Durham, NC 27708, USA.
| | - Deirdre C Lyons
- Department of Biology, Duke University, Durham, NC 27708, USA.
| | - Joshua E S Socolar
- Program in Computational Biology and Bioinformatics, Duke University, Durham, NC 27708, USA; Duke Center for Systems Biology, Duke University, Durham, NC 27708, USA; Department of Physics, Duke University, Durham, NC 27708, USA.
| | - David R McClay
- Program in Computational Biology and Bioinformatics, Duke University, Durham, NC 27708, USA; Duke Center for Systems Biology, Duke University, Durham, NC 27708, USA; Department of Biology, Duke University, Durham, NC 27708, USA.
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21
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Kumamoto T, Hanashima C. Neuronal subtype specification in establishing mammalian neocortical circuits. Neurosci Res 2014; 86:37-49. [PMID: 25019611 DOI: 10.1016/j.neures.2014.07.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2014] [Revised: 06/21/2014] [Accepted: 06/23/2014] [Indexed: 11/28/2022]
Abstract
The functional integrity of the neocortical circuit relies on the precise production of diverse neuron populations and their assembly during development. In recent years, extensive progress has been made in the understanding of the mechanisms that control differentiation of each neuronal type within the neocortex. In this review, we address how the elaborate neocortical cytoarchitecture is established from a simple neuroepithelium based on recent studies examining the spatiotemporal mechanisms of neuronal subtype specification. We further discuss the critical events that underlie the conversion of the stem amniotes cerebrum to a mammalian-type neocortex, and extend these key findings in the light of mammalian evolution to understand how the neocortex in humans evolved from common ancestral mammals.
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Affiliation(s)
- Takuma Kumamoto
- Laboratory for Neocortical Development, RIKEN Center for Developmental Biology, Kobe 650-0047, Japan
| | - Carina Hanashima
- Laboratory for Neocortical Development, RIKEN Center for Developmental Biology, Kobe 650-0047, Japan; Department of Biology, Graduate School of Science, Kobe University, Kobe 657-8501, Japan.
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22
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Brzezinski JA, Uoon Park K, Reh TA. Blimp1 (Prdm1) prevents re-specification of photoreceptors into retinal bipolar cells by restricting competence. Dev Biol 2013; 384:194-204. [PMID: 24125957 DOI: 10.1016/j.ydbio.2013.10.006] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2013] [Revised: 10/02/2013] [Accepted: 10/04/2013] [Indexed: 12/14/2022]
Abstract
During retinal development, photoreceptors and bipolar cells express the transcription factor Otx2. Blimp1 is transiently expressed in Otx2+ cells. Blimp1 deletion results in excess bipolar cell formation at the expense of photoreceptors. In principle, Blimp1 could be expressed only in Otx2+ cells that are committed to photoreceptor fate. Alternatively, Blimp1 could be expressed broadly in Otx2+ cells and silenced to allow bipolar cell development. To distinguish between these alternatives, we followed the fate of Blimp1 expressing cells using Blimp1-Cre mice and Lox-Stop-Lox reporter strains. We observed that Blimp1+ cells gave rise to all photoreceptors, but also to one third of bipolar cells, consistent with the latter alternative: that Blimp1 inhibits bipolar competence in Otx2+ cells and must be silenced to allow bipolar cell generation. To further test this hypothesis, we looked for transitioning rod photoreceptors in Blimp1 conditional knock-out (CKO) mice carrying the NRL-GFP transgene, which specifically labels rods. Control animals lacked NRL-GFP+ bipolar cells. In contrast, about half of the precociously generated bipolar cells in Blimp1 CKO mice co-expressed GFP, suggesting that rods become re-specified as bipolar cells. Birthdating analyses in control and Blimp1 CKO mice showed that bipolar cells were birthdated as early as E13.5 in Blimp1 CKO mice, five days before this cell type was generated in the wild-type retina. Taken together, our data suggest that early Otx2+ cells upregulate photoreceptor and bipolar genes, existing in a bistable state. Blimp1 likely forms a cross-repressive network with pro-bipolar factors such that the winner of this interaction stabilizes the photoreceptor or bipolar state, respectively.
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Affiliation(s)
- Joseph A Brzezinski
- Department of Ophthalmology. University of Colorado School of Medicine, Aurora, CO 80045, USA.
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23
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Abstract
It has long been appreciated that the inheritance of maternal cytoplasmic determinants from different regions of the egg can lead to differential specification of blastomeres during cleavage. Localized RNAs are important determinants of cell fate in eggs and embryos but are also recognized as fundamental regulators of cell structure and function. This chapter summarizes recent molecular and genetic experiments regarding: (1) mechanisms that regulate polarity during different stages of vertebrate oogenesis, (2) pathways that localize presumptive protein and RNA determinants within the polarized oocyte and egg, and (3) how these determinants act in the embryo to determine the ultimate cell fates. Emphasis is placed on studies done in Xenopus, where extensive work has been done in these areas, and comparisons are drawn with fish and mammals. The prospects for future work using in vivo genome manipulation and other postgenomic approaches are also discussed.
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