Expression of epidermal growth factor family gene members in early mouse development

The role of DNA methylation in syndromic and non-syndromic congenital heart disease

Congenital heart disease (CHD) is a common structural birth defect worldwide, and defects typically occur in the walls and valves of the heart or enlarged blood vessels. Chromosomal abnormalities and genetic mutations only account for a small portion of the pathogenic mechanisms of CHD, and the etiology of most cases remains unknown. The role of epigenetics in various diseases, including CHD, has attracted increased attention. The contributions of DNA methylation, one of the most important epigenetic modifications, to CHD have not been illuminated. Increasing evidence suggests that aberrant DNA methylation is related to CHD. Here, we briefly introduce DNA methylation and CHD and then review the DNA methylation profiles during cardiac development and in CHD, abnormalities in maternal genome-wide DNA methylation patterns are also described. Whole genome methylation profile and important differentially methylated genes identified in recent years are summarized and clustered according to the sample type and methodologies. Finally, we discuss the novel technology for and prospects of CHD-related DNA methylation.

Ectopic expression of Cripto-1 in transgenic mouse embryos causes hemorrhages, fatal cardiac defects and embryonic lethality

Targeted disruption of Cripto-1 in mice caused embryonic lethality at E7.5, whereas we unexpectedly found that ectopic Cripto-1 expression in mouse embryos also led to embryonic lethality, which prompted us to characterize the causes and mechanisms underlying embryonic death due to ectopic Cripto-1 expression. RCLG/EIIa-Cre embryos displayed complex phenotypes between embryonic day 14.5 (E14.5) and E17.5, including fatal hemorrhages (E14.5-E15.5), embryo resorption (E14.5-E17.5), pale body surface (E14.5-E16.5) and no abnormal appearance (E14.5-E16.5). Macroscopic and histological examination revealed that ectopic expression of Cripto-1 transgene in RCLG/EIIa-Cre embryos resulted in lethal cardiac defects, as evidenced by cardiac malformations, myocardial thinning, failed assembly of striated myofibrils and lack of heartbeat. In addition, Cripto-1 transgene activation beginning after E8.5 also caused the aforementioned lethal cardiac defects in mouse embryos. Furthermore, ectopic Cripto-1 expression in embryonic hearts reduced the expression of cardiac transcription factors, which is at least partially responsible for the aforementioned lethal cardiac defects. Our results suggest that hemorrhages and cardiac abnormalities are two important lethal factors in Cripto-1 transgenic mice. Taken together, these findings are the first to demonstrate that sustained Cripto-1 transgene expression after E11.5 causes fatal hemorrhages and lethal cardiac defects, leading to embryonic death at E14.5-17.5.

Breaking down pluripotency in the porcine embryo reveals both a premature and reticent stem cell state in the inner cell mass and unique expression profiles of the naive and primed stem cell states

To date, it has been difficult to establish bona fide porcine embryonic stem cells (pESC) and stable induced pluripotent stem cells. Reasons for this remain unclear, but they may depend on inappropriate culture conditions. This study reports the most insights to date on genes expressed in the pluripotent cells of the porcine embryo, namely the inner cell mass (ICM), the trophectoderm-covered epiblast (EPI), and the embryonic disc epiblast (ED). Specifically, we reveal that the early porcine ICM represents a premature state of pluripotency due to lack of translation of key pluripotent proteins, and the late ICM enters a transient, reticent pluripotent state which lacks expression of most genes associated with pluripotency. We describe a unique expression profile of the porcine EPI, reflecting the naive stem cell state, including expression of OCT4, NANOG, CRIPTO, and SSEA-1; weak expression of NrOB1 and REX1; but very limited expression of genes in classical pathways involved in regulating pluripotency. The porcine ED, reflecting the primed stem cell state, can be characterized by the expression of OCT4, NANOG, SOX2, KLF4, cMYC, REX1, CRIPTO, and KLF2. Further cell culture experiments using inhibitors against FGF, JAK/STAT, BMP, WNT, and NODAL pathways on cell cultures derived from day 5 and 10 embryos reveal the importance of FGF, JAK/STAT, and BMP signaling in maintaining cell proliferation of pESCs in vitro. Together, this article provides new insights into the regulation of pluripotency, revealing unique stem cell states in the different porcine stem cell populations derived from the early developing embryo.

Reviewing and updating the major molecular markers for stem cells

Stem cells (SC) are able to self-renew and to differentiate into many types of committed cells, making SCs interesting for cellular therapy. However, the pool of SCs in vivo and in vitro consists of a mix of cells at several stages of differentiation, making it difficult to obtain a homogeneous population of SCs for research. Therefore, it is important to isolate and characterize unambiguous molecular markers that can be applied to SCs. Here, we review classical and new candidate molecular markers that have been established to show a molecular profile for human embryonic stem cells (hESCs), mesenchymal stem cells (MSCs), and hematopoietic stem cells (HSCs). The commonly cited markers for embryonic ESCs are Nanog, Oct-4, Sox-2, Rex-1, Dnmt3b, Lin-28, Tdgf1, FoxD3, Tert, Utf-1, Gal, Cx43, Gdf3, Gtcm1, Terf1, Terf2, Lefty A, and Lefty B. MSCs are primarily identified by the expression of CD13, CD29, CD44, CD49e, CD54, CD71, CD73, CD90, CD105, CD106, CD166, and HLA-ABC and lack CD14, CD31, CD34, CD45, CD62E, CD62L, CD62P, and HLA-DR expression. HSCs are mainly isolated based on the expression of CD34, but the combination of this marker with CD133 and CD90, together with a lack of CD38 and other lineage markers, provides the most homogeneous pool of SCs. Here, we present new and alternative markers for SCs, along with microRNA profiles, for these cells.

Nkx2-5 Regulates Tdgf1 (Cripto) Early During Cardiac Development

Congenital Heart Disease (CHD) is the most frequent and deadly birth defect. Patients with CHD that survive the neonatal period often progress to develop advanced heart failure requiring specialized treatment including cardiac transplantation. A full understanding of the transcriptional networks that direct cardiac progenitors during heart development will enhance our understanding of both normal cardiac function and pathological states. These findings will also have important applications for emerging therapies and the treatment of congenital heart disease. Furthermore, a number of shared transcriptional pathways or networks have been proposed to regulate the development and regeneration of tissues such as the heart. We have utilized transgenic technology to isolate and characterize cardiac progenitor cells from the developing mouse heart and have begun to define specific transcriptional networks of cardiovascular development. Initial studies identified Tdgf1 as a potential target of Nkx2-5. To mechanistically dissect the regulation of this molecular program, we utilized an array of molecular biological techniques to confirm that Nkx2-5 is an upstream regulator of the Tdgf1 gene in early cardiac development. These studies further define Nkx2-5 mediated transcriptional networks and enhance our understanding of cardiac morphogenesis.

Uni-directional differentiation of mouse embryonic stem cells into neurons by the neural stem sphere method

We previously showed that our neural stem sphere (NSS) method promotes the neuronal differentiation of mouse, monkey and human embryonic stem (ES) cells. Here we analyzed changes in expression of marker genes and proteins during neuronal differentiation. When cultured in astrocyte-conditioned medium (ACM) under free-floating conditions, colonies of ES cells formed floating cell spheres, which, within 4 days, gave rise to NSSs. In the spheres, the expression of ES cell marker genes was consistently down-regulated, while expression of an epiblast marker was transiently up-regulated, beginning on day 2, and the expression of neuroectoderm, neural stem cell and neuron markers was up-regulated, beginning on days 3, 4 and 6, respectively. The expression of the marker genes was consistent with that of marker proteins. The time course of expression of these markers in the spheres resembled that of neuronal differentiation from the inner cell mass (ICM) cells of blastula. In contrast, the expression of endoderm, mesoderm, epidermis, astrocyte and oligodendrocyte markers was low and not up-regulated during differentiation. Only a small number of apoptotic cells were present in the spheres. These results suggest that mouse ES cells uni-directionally differentiate into neurons via epiblast cells, neuroectodermal cells and neural stem cells.

Emerging roles of nodal and Cripto-1: from embryogenesis to breast cancer progression

Breast carcinoma cells and embryonic progenitors similarly implement stem cell-associated signaling pathways to sustain continued growth and plasticity. Indeed, recent studies have implicated signaling pathways, including those associated with the Notch, and Transforming Growth Factor-Beta (TGF-beta) superfamilies, as instrumental to both embryological development and breast cancer progression. In particular, Nodal, an embryonic morphogen belonging to the TGF-beta superfamily, and its co-receptor, Cripto-1, are requisite to both embryogenesis and mammary gland maturation. Moreover, these developmental proteins have been shown to promote breast cancer progression. Here, we review the role of Nodal and its co-receptor Cripto-1 during development and we describe how this signaling pathway may be involved in breast cancer tumorigenesis. Moreover, we emphasize the potential utility of this signaling pathway as a novel target for the treatment and diagnosis of breast cancer.

Human embryonic stem cells and cardiac repair

The muscle lost after a myocardial infarction is replaced with noncontractile scar tissue, often initiating heart failure. Whole-organ cardiac transplantation is the only currently available clinical means of replacing the lost muscle, but this option is limited by the inadequate supply of donor hearts. Thus, cell-based cardiac repair has attracted considerable interest as an alternative means of ameliorating cardiac injury. Because of their tremendous capacity for expansion and unquestioned cardiac potential, pluripotent human embryonic stem cells (hESCs) represent an attractive candidate cell source for obtaining cardiomyocytes and other useful mesenchymal cell types for such therapies. Human embryonic stem cell-derived cardiomyocytes exhibit a committed cardiac phenotype and robust proliferative capacity, and recent testing in rodent infarct models indicates that they can partially remuscularize injured hearts and improve contractile function. Although the latter successes give good reason for optimism, considerable challenges remain in the successful application of hESCs to cardiac repair, including the need for preparations of high cardiac purity, improved methods of delivery, and approaches to overcome immune rejection and other causes of graft cell death. This review will describe the phenotype of hESC-derived cardiomyocytes and preclinical experience with these cells and will consider strategies to overcoming the aforementioned challenges.

Directed neural differentiation of human embryonic stem cells via an obligated primitive anterior stage

Understanding neuroectoderm formation and subsequent diversification to functional neural subtypes remains elusive. We show here that human embryonic stem cells (hESCs) differentiate to primitive neuroectoderm after 8-10 days. At this stage, cells uniformly exhibit columnar morphology and express neural markers, including anterior but not posterior homeodomain proteins. The anterior identity of these cells develops regardless of morphogens present during initial neuroectoderm specification. This anterior phenotype can be maintained or transformed to a caudal fate with specific morphogens over the next week, when cells become definitive neuroepithelia, marked by neural tube-like structures with distinct adhesion molecule expression, Sox1 expression, and a resistance to additional patterning signals. Thus, primitive neuroepithelia represents the earliest neural cells that possess the potential to differentiate to regionally specific neural progenitors. This finding offers insights into early human brain development and lays a foundation for generating neural cells with correct positional and transmitter profiles. Disclosure of potential conflicts of interest is found at the end of this article.

Nodal-dependant Cripto signaling in ES cells: from stem cells to tumor biology

Embryonic stem (ES) cells have provided a valid model to understand early events of mammalian lineage specification and differentiation, leading to important insights into the mechanisms that control embryogenesis at the molecular and cellular levels. Furthermore, ES cells have recently evoked great scientific interest as ideal candidates for the generation of tissues for transplantation therapies. In this respect, particular attention has been paid to the molecules and signaling pathways triggering ES cell differentiation. The EGF-CFC Cripto protein is a key regulator of ES cells fate. The cripto gene is expressed both in ES cells and during the early phases of embryo development, while, in the adult, it is reactivated in a wide range of epithelial cancers. This review will discuss recent findings on the molecular basis of Cripto signaling in ES cell differentiation, providing an intriguing link between stem cell and tumor biology.

Teratogenic effects of retinoic acid are modulated in mice lacking expression of epidermal growth factor and transforming growth factor-alpha

BACKGROUND

Epidermal growth factor (EGF) and transforming growth factor-alpha (TGFalpha) regulate cell proliferation and differentiation in the embryo. The induction of cleft palate (CP) by all trans-retinoic acid (RA) was associated with altered expression of TGFalpha, EGF receptor, and binding of EGF. This study uses knockout (KO) mice to examine the roles of EGF and TGFalpha in teratogenic responses of embryos exposed to RA.

METHODS

Pregnant wild-type (WT) mice of mixed genetic background, EGF KO, C57BL/6J, and TGFalpha KO mice were given a single oral dose of RA (100 mg/kg, 10 ml/kg) or corn oil on GD 10 at 12 PM, GD 11 at 12 PM or 4 PM, or GD 12 at 8 AM or 12 PM (plug day = GD 0). GD 18 fetuses were examined for external, visceral, and skeletal effects.

RESULTS

After exposure to RA on GD 12, the incidence of CP in EGF KO was significantly reduced relative to WT. In TGFalpha KO fetuses, RA exposure on GD 10 increased the incidence of CP versus C57BL/6J. The incidence of skeletal defects in the limbs, vertebrae, sternebrae, and ribs were also affected by lack of expression of EGF or TGFalpha with region-specific amelioration or exacerbation of the effects of RA. In TGFalpha KO fetuses, incidences of forelimb long bone and digit defects increased relative to C57BL/6J. In EGF KO fetuses, relative to WT, the incidence of hindlimb oligodactyly was increased. In EGF KO, but not WT, RA produced short, bent radius, humerus, and ulna. Both TGFalpha and EGF KO mice had increased incidences of dilation of the renal pelvis and this was reduced by RA.

CONCLUSIONS

RA exposure produced skeletal and visceral defects in all genotypes; however, EGF or TGFalpha KO influenced the incidence and severity of defects. This study supports a role for EGF and TGFalpha in the response to RA.

Cripto-1: an oncofetal gene with many faces

Human Cripto-1 (CR-1), a member of the epidermal growth factor (EGF)-CFC family, has been implicated in embryogenesis and in carcinogenesis. During early vertebrate development, CR-1 functions as a co-receptor for Nodal, a transforming growth factor beta (TGFbeta) family member and is essential for mesoderm and endoderm formation and anterior-posterior and left-right axis establishment. In adult tissues, CR-1 is expressed at a low level in all stages of mammary gland development and expression increases during pregnancy and lactation. Overexpression of CR-1 in mouse mammary epithelial cells leads to their transformation in vitro and, when injected into mammary glands, produces ductal hyperplasias. CR-1 can also enhance migration, invasion, branching morphogenesis and epithelial to mesenchymal transition (EMT) of several mouse mammary epithelial cell lines. Furthermore, transgenic mouse studies have shown that overexpression of a human CR-1 transgene in the mammary gland under the transcriptional control of the mouse mammary tumor virus (MMTV) promoter results in mammary hyperplasias and papillary adenocarcinomas. Finally, CR-1 is expressed at high levels in approximately 50 to 80% of different types of human carcinomas, including breast, cervix, colon, stomach, pancreas, lung, ovary, and testis. In conclusion, EGF-CFC proteins play dual roles as embryonic pattern formation genes and as oncogenes. While during embryogenesis EGF-CFC proteins perform specific and regulatory functions related to cell and tissue patterning, inappropriate expression of these molecules in adult tissues can lead to cellular proliferation and transformation and therefore may be important in the etiology and/or progression of cancer.

Imaging filopodia dynamics in the mouse blastocyst

During mammalian development, the first cell lineage diversification event occurs in the blastocyst, when the trophectoderm (TE) and the inner cell mass (ICM) become established. Part of the TE (polar) remains in contact with the ICM and differs from the mural TE (mTE) which is separated from the ICM by a cavity known as the blastocoele. The presence of filopodia connecting ICM cells with the distant mural TE cells through the blastocoelic fluid was investigated in this work. We describe two types of actin-based cell projections found in freshly dissected and in vitro cultured expanding blastocysts: abundant short filopodia projecting into the blastocoelic cavity that present a continuous undulating behavior; and long, thin traversing filopodia connecting the mural TE with the ICM. Videomicroscopy analyses revealed the presence of vesicle-like structures moving along traversing filopodia and dynamic cytoskeletal rearrangements. These observations, together with immunolocalization of the FGFR2 and the ErbB3 receptors to these cell extensions, suggest that they display signal transduction activity. We propose that traversing filopodia are employed by mitotic mTE cells to receive the required signals for cell division after they become distant to the ICM.

Unique gene expression signatures of independently-derived human embryonic stem cell lines

Human embryonic stem cells (hESCs) have the potential to differentiate to diverse cell types. This ability endows hESCs with promise for the development of novel therapeutics, as well as promise for the development of a rigorous genetic system to probe human gene function. However, in spite of the impending utility of hESCs for clinical and basic applications, little is known about their fundamental properties. Recent reports have documented transcriptional profiles of mouse embryonic stem cells (mESCs), adult stem cells and a single hESC line, H9. To date, however, the transcriptional profiles of independently-derived hESC lines have not been compared. In order to examine the similarities and differences in multiple hESC lines, we compared gene expression profiles of the HSF-1, HSF-6 and H9 lines. We found that the majority of genes examined were expressed in all three cell lines. However, we also observed that each line possessed a unique expression signature; the expression of many genes was limited to just one or two hESC lines. We suggest that the observed differences in gene expression between independently-derived hESC lines may reflect inherent differences in the initial culture of each line and/or the underlying genetics of the embryos from which the lines were derived.

Molecules in blastocyst implantation: uterine and embryonic perspectives

Synchronized development of the embryo to the active stage of the blastocyst, differentiation of the uterus to the receptive state, and a "cross talk" between the blastocyst and uterine luminal epithelium are essential to the process of implantation. In spite of considerable accumulation of information and the present state of the knowledge, our understanding of the definitive mechanisms that regulate these events remains elusive. Although there are species variations in the process of implantation, many basic similarities do exist among various species. This review focuses on specific aspects of the implantation process in mice with the hope that many of the findings will be relevant to the process in humans. To establish signaling mechanisms of embryo-uterine interactions during implantation, studies on both embryonic and uterine consequences are required to generate more meaningful information. Due to ethical restriction and experimental limitation, it is difficult to generate such information in humans. This review has attempted to provide a comprehensive, but not complete, narration of a number of embryonic and uterine factors that are involved in the process of implantation in autocrine, paracrine, and/or juxtacrine manners in mice at the physiological, cellular, molecular, and genetic levels.

Role of the EGF-CFC gene cripto in cell differentiation and embryo development

The EGF-CFC proteins have been recently recognized as a novel family of extracellular factors required during early vertebrate development. Cripto is the founder member of the EGF-CFC family initially related to the epidermal growth factor (EGF); its expression is increased in human colon, gastric, pancreatic and lung carcinoma and in different types of both mouse and human breast carcinomas. Genetic studies in the mouse have established an essential role of cripto in the formation and correct positioning of the anterior-posterior axis. Furthermore, the absence of cripto results in a defective precardiac mesoderm, unable to differentiate into functional cardiomyocytes. Although mouse and human Cripto have been shown to activate the ras/raf/MAP kinase pathway in mammary epithelial cell lines, genetic evidence in Zebrafish has been provided for a relationship between the EGF-CFC proteins and Nodal, a member of the transforming growth factor family. Here we review the biological role of cripto in development and differentiation, pointing out recent findings on the biochemical interactions of Cripto, Nodal and Activin-like receptors.

Cripto: a tumor growth factor and more

Cripto, a growth factor with an EGF-like domain, and the first member of the EGF-CFC family of genes to be sequenced and characterized, contributes to deregulated growth of cancer cells. A role for Cripto in tumor development has been described in the human and the mouse. Members of the EGF-CFC family are found only in vertebrates: CFC proteins in zebrafish, Xenopus, chick, mouse and human have been characterized and indicate some common general functions in development. Cripto expression was first found in human and mouse embryonal carcinoma cells and male teratocarcinomas, and was demonstrated to be over-expressed in breast, cervical, ovarian, gastric, lung, colon, and pancreatic carcinomas in contrast to normal tissues where Cripto expression was invariably low or absent. Cripto may play a role in mammary tumorigenesis, since in vitro, Cripto induces mammary cell proliferation, reduces apoptosis, increases cell migration, and inhibits milk protein expression. This prediction is strengthened by observations of Cripto expression in 80% of human and mouse mammary tumors. At least three important roles for Cripto in development have created considerable interest, and each activity may be distinct in its mechanism of receptor signaling. One role is in the patterning of the anterior-posterior axis of the early embryo, a second is a crucial role in the development of the heart, and a third is in potentiating branching morphogenesis and modulating differentiation in the developing mammary gland. Whether these properties are functions of different forms of Cripto, different Cripto receptors or the distinct domains within this 15-38 kDa glycoprotein are examined here, but much remains to be revealed about this evolutionarily conserved gene product. Since all Cripto receptors have not yet been determined with certainty, future possible uses as therapeutic targets remain to be developed. Cripto is released or shed from expressing cells and may serve as an accessible marker gene in the early to mid-progressive stages of breast and other cancers. Meanwhile some speculations on possible receptor complexes for Cripto signaling in mammary cells are offered here as a spur to further discoveries.

Bmp2b and Oep promote early myocardial differentiation through their regulation of gata5

Members of both the bone morphogenetic protein (Bmp) and EGF-CFC families have been implicated in vertebrate myocardial development. Zebrafish swirl (swr) encodes Bmp2b, a member of the Bmp family required for patterning the dorsoventral axis. Zebrafish one-eyed pinhead (oep) encodes a maternally and zygotically expressed member of the EGF-CFC family essential for Nodal signaling. Both swr/bmp2b and oep mutants exhibit severe defects in myocardial development. swr/bmp2b mutants exhibit reduced or absent expression of nkx2.5, an early marker of the myocardial precursors. Embryos lacking zygotic oep (Zoep mutants) display cardia bifida and, as we show here, also display reduced or absent nkx2.5 expression. Recently, we have demonstrated that the zinc finger transcription factor Gata5 is an essential regulator of nkx2.5 expression. In this paper, we investigate the relationships between bmp2b, oep, gata5, and nkx2.5. We show that both swr/bmp2b and Zoep mutants exhibit defects in gata5 expression in the myocardial precursors. Forced expression of gata5 in swr/bmp2b and Zoep mutants restores robust nkx2.5 expression. Moreover, overexpression of gata5 in Zoep mutants restores expression of cmlc1, a myocardial sarcomeric gene. These results indicate that both Bmp2b and Oep regulate gata5 expression in the myocardial precursors, and that Gata5 does not require Bmp2b or Oep to promote early myocardial differentiation. We conclude that Bmp2b and Oep function at least partly through Gata5 to regulate nkx2.5 expression and promote myocardial differentiation. We integrate these and other data to propose a pathway of the molecular events regulating early myocardial differentiation in zebrafish.

CHAMP, a novel cardiac-specific helicase regulated by MEF2C

MEF2C is a MADS-box transcription factor required for cardiac myogenesis and morphogenesis. In MEF2C mutant mouse embryos, heart development arrests at the looping stage (embryonic day 9.0), the future right ventricular chamber fails to form, and cardiomyocyte differentiation is disrupted. To identify genes regulated by MEF2C in the developing heart, we performed differential array analysis coupled with subtractive cloning using RNA from heart tubes of wild-type and MEF2C-null embryos. Here, we describe a novel MEF2C-dependent gene that encodes a cardiac-restricted protein, called CHAMP (cardiac helicase activated by MEF2 protein), that contains seven conserved motifs characteristic of helicases involved in RNA processing, DNA replication, and transcription. During mouse embryogenesis, CHAMP expression commences in the linear heart tube at embryonic day 8.0, shortly after initiation of MEF2C expression in the cardiogenic region. Thereafter, CHAMP is expressed specifically in embryonic and postnatal cardiomyocytes. At the trabeculation stage of heart development, CHAMP expression is highest in the trabecular region in which cardiomyocytes have exited the cell cycle and is lowest in the proliferative compact zone. These findings suggest that CHAMP acts downstream of MEF2C in a cardiac-specific regulatory pathway for RNA processing and/or transcriptional control.

Immunocytochemical localization of epidermal growth factor receptor in early embryos of the Japanese medaka fish (Oryzias latipes)

This study was undertaken to localize epidermal growth factor receptor (EGFR) during early development of Japanese medaka embryos using immunocytochemistry. Specific staining was observed in all stages studied. All of the cells of the embryonic disc from the germinal disc (1 cell) through the late high blastula stages stained moderately for EGFR. Beginning with the flat blastula stage, the surface and lateral cells of the embryonic disc and the cells migrating around the yolk stained intensely for EGFR, and this continued throughout the study period. The presence of the keel at the late gastrula stage did not affect the moderate staining of the majority of the embryonic disc cells. When somites first appeared, the keel region stained less intensely than before, but scattered individual cells stained intensely for EGFR. Embryos with 12 somites had a neural tube that was lightly stained except for a few intensely stained individual cells. The neural tube, notochord and somites in 24-somite embryos lacked immunostaining. However, the surface epithelium, aorta, intestinal epithelium and pronephric duct demonstrated EGFR immunostaining. This study demonstrates that EGFR is present during medaka development and supports the hypothesis that EGFR ligands are important during cleavage, gastrulation and early organogenesis.

The initial phase of embryonic patterning in mammals

Although specification of the antero-posterior axis is a critical intial step in development of the fetus, it is not known either how, or at what stage in development, this process begins. Such information is vital for understanding not only normal development in mammals but also monozygotic twinning, which, at least in man, is associated with a significantly increased incidence of birth defects. According to recent studies in the mouse, specification of the fetal anteroposterior axis begins well before gastrulation, and probably even before the conceptus implants. Moreover, evidence is accruing that the origin of relevant asymmetries depends on information that is already present in the zygote before it embarks on cleavage. Hence, early development in mammals does not differ as markedly from that in other animals as has generally been assumed. Consequently, at present, the possibility of adverse effects of techniques used to assist human reproduction cannot be disregarded.

Subtractive hybridization identifies chick-cripto, a novel EGF-CFC ortholog expressed during gastrulation, neurulation and early cardiogenesis

EGF-CFC genes encode a novel class of extracellular, membrane-associated proteins that notably play an important role during vertebrate gastrulation. Whereas the two cysteine-rich domains that characterize these proteins, namely the extracellular EGF-like and the CFC domain, are known to be encoded by two evolutionarily conserved exons, it is generally assumed, based on weak primary sequence identity, that the remaining parts of the protein differ among vertebrates, suggesting that known members of the EGF-CFC family do not represent true orthologs. Here, by characterizing the full cDNA and genomic sequences of a new EGF-CFC gene in chick, and by comparing them with their counterparts in human (CRIPTO), mouse (cripto and cryptic), Xenopus (FRL-1) and zebrafish (one-eyed pinhead), we show that all EGF-CFC genes share an identical genomic organization over the entire coding region. Not only are the central two exons (coding for the EGF-like and CFC motifs) conserved, but also conserved are the total number of exons, their size, their intron phase and their correlation with discrete protein modules, in particular those modules that allow the EGF-CFC motif to become membrane-associated. Therefore, despite apparent divergence between their 5' and 3'-terminal exons, all known CRIPTO-related genes are structurally orthologous. We named this novel ortholog in bird, chick-cripto. We report the mRNA distribution of chick-cripto, which begins in the epiblast of the gastrula, with a pattern similar to EGF-CFC genes of other vertebrates.

Membrane-anchorage of Cripto protein by glycosylphosphatidylinositol and its distribution during early mouse development

cripto is the original member of the family of EGF-CFC genes, recently recognized as novel extracellular factors essential for vertebrate development. During the early stages of mouse gastrulation, cripto mRNA is detected in mesodermal cells; later, cripto mRNA is detected only in the truncus arteriosus of the developing heart. Here we describe the in vivo distribution of Cripto protein throughout mouse embryo development and show that cripto mRNA and protein colocalize. By means of immunofluorescence analysis and biochemical characterization, we show that Cripto is a membrane-bound protein anchored to the lipid bilayer by a glycosylphosphatidylinositol (GPI) moiety. We suggest that presentation of Cripto on the cell surface via a GPI-linkage is important in determining the spatial specificity of cell-cell interactions that play a critical role in the early patterning of the embryo.

Molecular phenotype of the human oocyte by PCR-SAGE

Consecutive application of PCR and serial analysis of gene expression (SAGE) was used to generate a catalog of approximately 50, 000 SAGEtags from nine human oocytes. Matches for known genes were identified using the National Institutes of Health SAGEtag database. This database links directly to the UniGene database, providing rapid discrimination between SAGEtags that match known genes and expressed sequence tags and those that currently have no match. Matches in the oocyte SAGE catalog were found for surface receptors, second-messenger systems, and cytoskeletal, apoptotic, and secreted proteins. Many of these proteins were not previously known to be expressed in mammalian oocytes. The relative abundances of transcripts for cytoskeletal proteins and proteins known to be in oocytes are consistent with their documented expression, suggesting an absence of representational distortion by the PCR step. The expression profile of the human oocyte may help identify factors that reprogram somatic cell nuclei to totipotency.

Beta-catenin is a major tyrosine-phosphorylated protein during mouse oocyte maturation and preimplantation development

During mouse preimplantation development, the components of the E-cadherin-catenin complex are derived from both maternal and zygotic gene activity and the adhesion complex is increasingly accumulated and stored in a nonfunctional form, ready to be used for compaction and the formation of the trophectoderm cell layer (Ohsugi et al., Dev. Dyn. 206:391-402, 1996). Here, we show that beta-catenin is a major tyrosine-phosphorylated protein in oocytes and early cleavage-stage embryos and that the relative amount of phosphorylated beta-catenin is greatly reduced during the morula-blastocyst transition. Peptide-specific antibodies indicate that beta-catenin undergoes conformational changes and/or that the carboxy-terminal region of beta-catenin is blocked during preimplantation development. Moreover, the availability of a carboxy-terminal epitope seems to depend on the tyrosine phosphorylation state of beta-catenin and becomes unmasked when oocytes are treated with the tyrosine kinase inhibitor genistein. Our results suggest that tyrosine phosphorylation of beta-catenin represents a molecular mechanism to keep the accumulating E-cadherin adhesion complex in a nonfunctional form. Dev Dyn 1999;216:168-176.

Abrogation of the Cripto gene in mouse leads to failure of postgastrulation morphogenesis and lack of differentiation of cardiomyocytes

Cripto-1(Cr1) protein encoded by the tdgf1 gene, is a secreted growth factor that is expressed early in embryonic development and is re-expressed in some tumors of the breast and colon. During embryonic development, Cr1 is expressed in inner cell mass cells and the primitive streak, and later is restricted to the developing heart. To investigate the role of Cr1 during mouse development, mice were generated that contain a null mutation of both Cr1 genes, derived from homologous recombination in embryonic stem cells. No homozygous Cr1−/− mice were born, indicating that Cr1 is necessary for embryonic development. Embryos initiated gastrulation and some embryos produced mesoderm up to day E7.5. Increasingly aberrant morphogenesis gave rise to disordered neuroepithelium that failed to produce a recognizable neural tube, or head-fold. Although some biochemical markers of differentiating ectoderm, mesoderm and endoderm were expressed, all the cardiac-specific markers were absent from day E8.7 embryos: (α)MHC, betaMHC, MLC2A, MLC2V and ANF, whereas they were expressed in wild-type embryos. The yolk sac and placental tissues continued development in the absence of the embryo until day E9.5 but lacked large yolk sac blood vessels. Chimeric mice were constructed by microinjection of double targeted Cr1(−/−)embryonic stem cells into normal C57BL/6 blastocysts. The Cr1 produced by the normal C57BL/6 cells fully rescued the phenotype of Cr1(−/−) cells, indicating that Cr1 protein acted in a paracrine manner. Cells derived from the embryo proliferated and migrated poorly and had different adhesion properties compared to wild type. Therefore, lethality in the absence of Cr1, likely resulted largely from defective precardiac mesoderm that was unable to differentiate into functional cardiomyocytes.

Cripto: a novel epidermal growth factor (EGF)-related peptide in mammary gland development and neoplasia

Growth and morphogenesis in the mammary gland depend on locally derived growth factors such as those in the epidermal growth factor (EGF) superfamily. Cripto-1 (CR-1, human; Cr-1, mouse)--also known as teratocarcinoma-derived growth factor-1--is a novel EGF-related protein that induces branching morphogenesis in mammary epithelial cells both in vitro and in vivo and inhibits the expression of various milk proteins. In the mouse, Cr-1 is expressed in the growing terminal end buds in the virgin mouse mammary gland and expression increases during pregnancy and lactation. Cr-1/CR-1 is overexpressed in mouse and human mammary tumors and inappropriate overexpression of Cr-1 in mouse mammary epithelial cells can lead to the clonal expansion of ductal hyperplasias. Taken together, this evidence suggests that Cr-1/CR-1 performs a role in normal mammary gland development and that it might contribute to the early stages of mouse mammary tumorigenesis and the pathobiology of human breast cancer.

Cripto is required for correct orientation of the anterior-posterior axis in the mouse embryo

The anterior-posterior axis of the mouse embryo is established by two distinct organizing centres in the anterior visceral endoderm and the distal primitive streak. These organizers induce and pattern the head and trunk respectively, and have been proposed to be localized through coordinate cell movements that rotate a pre-existing proximal-distal axis. Here we show that correct localization of both head- and trunk-organizing centres requires Cripto, a putative signalling molecule that is a member of the EGF-CFC gene family. Before gastrulation, Cripto is asymmetrically expressed in a proximal-distal gradient in the epiblast, and subsequently is expressed in the primitive streak and newly formed embryonic mesoderm. A Cripto null mutation generated by targeted gene disruption results in homozygous Cripto-/- embryos that mostly consist of anterior neuroectoderm and lack posterior structures, thus resembling a head without a trunk. Notably, markers of the head organizer are located at the distal end of the embryo, whereas markers of the primitive streak are absent or localized to the proximal side. Our results indicate that Cripto signalling is essential for the conversion of a proximal-distal asymmetry into an orthogonal anterior-posterior axis.

Regulation of the fibroblast growth factor receptor 3 promoter and intron I enhancer by Sp1 family transcription factors

Fibroblast growth factor receptor 3 (FGFR3) has a complex spatial and temporal pattern of expression and is essential for the normal development of a diverse set of tissues. Recently, mutations have been identified in FGFR3 that result in constitutive tyrosine kinase activity and cause a number of different human skeletal disorders. To examine the regulatory mechanisms governing FGFR3 expression, the promoter for the FGFR3 gene was identified and characterized. It resides in a CpG island, which encompasses the 5' end of the FGFR3 gene and lacks classical cis-regulatory motifs. As little as 100 base pairs of sequence 5' to the initiation site can confer a 20-40-fold increase in transcriptional activity upon a promoter-less vector. The transcriptional activity of these cis-regulatory sequences is further stimulated by elements found within the first intron. Mapping of the enhancer activity found within intron I identified two purine-rich sequence motifs between +340 and +395. Electrophoretic mobility shift assays demonstrated that sequences within this region bind members of the Sp1 family of transcription factors. In a background lacking Sp1-like activity, we demonstrate that Sp1 can enhance transcription of the minimal promoter (which contains five classical Sp1 sites), whereas both Sp1 and Sp3 can enhance transcription through the elements found in intron I. Although these transcription factors are ubiquitously expressed, we demonstrate that the sequences between -220 and +609 of the FGFR3 gene are sufficient to promote the tissue-specific expression of a reporter gene in transgenic mice.

Positional cloning identifies zebrafish one-eyed pinhead as a permissive EGF-related ligand required during gastrulation

The zebrafish one-eyed pinhead (oep) mutation disrupts embryonic development, resulting in cyclopia and defects in endoderm, prechordal plate, and ventral neuroectoderm formation. We report the molecular isolation of oep using a positional cloning approach. The oep gene encodes a novel EGF-related protein with similarity to the EGF-CFC proteins cripto, cryptic, and FRL-1. Wild-type oep protein contains a functional signal sequence and is membrane-associated. Following ubiquitous maternal and zygotic expression, highest levels of oep mRNA are found in the gastrula margin and in axial structures and forebrain. Widespread misexpression of both membrane-attached and secreted forms of oep rescues prechordal plate and forebrain development in mutant embryos but does not lead to the ectopic induction of these cell types in wild-type fish. These results establish an essential but permissive role for an EGF-related ligand during vertebrate gastrulation.

Purification and characterization of a recombinant human cripto-1 protein

Cripto-1 (CR-1) is a novel protein that contains a modified EGF-like motif and that does not directly bind to any of the known erb B type-1 receptor tyrosine kinase receptors. To more clearly define the biological effects of CR-1 and to more adequately compare the structure-function relationships of CR-1 with other members of the EGF family of growth factors, we have expressed a modified, full-length recombinant human CR-1 protein (rhCR-1) in E. coli and have devised a procedure for the solubilization, refolding and purification of a biologically active form of this protein. We have generated the mature form of hCR-1 from computer assisted predictions of potential signal peptide cleavage sites. Expression of the modified rhCR-1 protein in E. coli was limited to the inclusion bodies. The rhCR-1 protein was found to be expressed at high levels in bacterial cells when fused to a histidine-tag sequence. Refolding of rhCR-1 was found to be difficult because of the large number of cysteine residues in the protein which results in protein aggregation. By chemically modifying the cysteine residues in the rhCR-1 protein with 3-trimethylammoniopropyl methanethiosulfonate, additional positive charges have been introduced into the protein by this disulfiding reagent. This modification facilitates solubilization of the protein when rhCR-1 is denatured. The solubilized, denatured protein was then purified by CM cation exchange and C4 reverse phase HPLC chromatography and refolded in a redox buffer. The refolded, modified rhCR-1 protein was found to be biologically active by its ability to inhibit beta-casein expression, to stimulate the tyrosine phosphorylation of Shc and the activation of MAPK and by its capacity to facilitate branching growth of mouse mammary epithelial cells in type I collagen gels.

Expression and function of amphiregulin during murine preimplantation development

Amphiregulin (Ar) is an EGF receptor ligand that functions to modulate the growth of both normal and malignant epithelial cells. We asked whether mouse preimplantation embryos express Ar, and if so, what the function of Ar is during preimplantation development. We used RT-PCR to show expression of Ar mRNA in mouse blastocysts, and using a polyclonal anti-Ar antibody and indirect immunofluorescence, we detected the presence of Ar protein in morula- and blastocyst-stage embryos. Ar protein was present in both the cytoplasm and nucleus in both morulae- and blastocyst-stage embryos, which is similar to Ar distribution in other cell types. Embryos cultured in Ar developed into blastocysts more quickly and also exhibited increased cell numbers compared to control embryos. In addition, 4-cell stage embryos cultured in an antisense Ar phosphorothioate-modified oligodeoxynucleotide (S-oligo) for 48 hr exhibited slower rates of blastocyst formation and reduced embryo cell numbers compared to embryos exposed to a random control S-oligo. TGF-alpha significantly improved blastocyst formation, but not cell numbers, for embryos cultured in the antisense Ar S-oligo. From these observations, we propose that Ar may function as an autocrine growth factor for mouse preimplantation embryos by promoting blastocyst formation and embryo cell number. We also propose that blastocyst formation is stimulated by Ar and TGF-alpha, while Ar appears to exert a greater stimulatory effect on cell proliferation than does TGF-alpha in these embryos.

A differential display strategy identifies Cryptic, a novel EGF-related gene expressed in the axial and lateral mesoderm during mouse gastrulation

We have developed a differential display screening approach to identify mesoderm-specific genes, relying upon the differentiation of embryonic stem (ES) cells in vitro. Using this strategy, we have isolated a novel murine gene that encodes a secreted molecule containing a variant epidermal growth factor-like (EGF) motif. We named this gene Cryptic, based on its predicted protein sequence similarity with Cripto, which encodes an EGF-related growth factor. Based on their strong sequence similarities, we propose that Cryptic, Cripto, and the Xenopus FRL-1 gene define a new family of growth factor-like molecules, which we name the ‘CFC’ (Cripto, Frl-1, and Cryptic) family. Analysis of Cryptic expression by in situ hybridization shows that it is expressed during gastrulation in two spatial domains that correspond to the axial and lateral mesoderm. In the first domain of expression, Cryptic expression is progressively localized to the anterior primitive streak, the head process, and the node and notochordal plate. In the second domain, Cryptic expression is initially concentrated in the lateral region of the egg cylinder, and is later found circumferentially in the intermediate and lateral plate mesoderm. Furthermore, Cryptic expression can also be detected at the early head-fold stage in the midline neuroectoderm, and consequently is an early marker for the prospective floor plate of the neural tube. Expression of Cryptic ceases at the end of gastrulation, and has not been observed in later embryonic stages or in adult tissues. Thus, Cryptic encodes a putative signaling molecule whose expression suggests potential roles in mesoderm and/or neural patterning during gastrulation.

Cell proliferation and expression of EGF, TGF-alpha, and EGF receptor in the developing primary palate

Growth factors such as epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) play an important role in cell proliferation during embryogenesis. The purposes of the study were to characterize the expression patterns of EGF and TGF-alpha and their receptor, EGF receptor (EGF-R), and to analyze regional patterns of cell proliferation during primary palate morphogenesis when facial primordia outgrow and fuse to form the premaxillary and upper lip regions. The expression of all molecules was studied with indirect immunohistochemistry with conventional and/or confocal microscopes in normal days 10 and 11 CD1 mice. 5-Bromodeoxyuridine (BrdU) and proliferating cell nuclear antigen (PCNA) were used as markers of cell proliferation. EGF, TGF-alpha, and EGF-R were found to have similar distribution patterns at all stages examined. In the anterior region of the face, the molecules were intensely localized at the tips and peripheral regions of the medial and lateral nasal prominences. Upon fusion of the facial prominences, all three molecules were present mainly at the fusion area and the tips and peripheral areas of the maxillary and nasal prominences. BrdU and PCNA were found to have distribution patterns similar to those of EGF, TGF-alpha, and EGF-R, with intense staining at the tips and peripheral regions of the facial prominences. These results show that EGF, TGF-alpha, and their receptor were expressed more intensely in regions of the developing primary palate where cell proliferation was most pronounced, and suggest that EGF, TGF-alpha, and EGF-R may play a role in cell proliferation during morphogenesis of the primary palate.