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C D Stern

Publications and source records attributed to C D Stern.

At least 55 records · Page 3Linked to original sources
PubMed1997

Early chick embryos in vitro.

In 1955, Denis New described a technique for the in vitro culture of early avian embryos that has formed the basis for nearly all of the experimental embryological studies performed on these species since that day. Many modifications to this technique have also been described in these four decades for specific experimental purposes. Here, we review the effects of some parameters that appear to be important for different aspects of the growth of embryos in this type of culture, and conduct a small experimental comparison between different modifications of the technique as described by various authors. We conclude that the original technique still compares favorably with its alternatives.

Animals↗
PubMed1996

The Le(x) carbohydrate sequence is recognized by antibody to L5, a functional antigen in early neural development.

The L5 antigenic determinant was previously suggested to be a carbohydrate epitope present on murine cell recognition molecules in the developing brain and to be an early neural marker in the chick embryo. Here, we show that L5 immunoreactivity is associated with complex-type N-glycosidic oligosaccharides. To identify the carbohydrate structure recognized by the L5 antibody, we investigate its binding to N-linked oligosaccharides derived from L5 glycoproteins and to known glycans. Results of mass spectrometric analyses of L5-positive neoglycolipids prepared from L5 glycoproteins are consistent with those for N-glycans containing a 3-fucosyl N-acetyllactosamine sequence. We also investigate L5 binding to structurally defined, lipid-linked oligosaccharides based on the blood group type I and II backbones. Chromatogram binding assays, ELISA, and inhibition studies show that the antibody reacts strongly with carbohydrate chains presenting the 3-fucosyl N-acetyllactosamine sequence [Lewisx (Le(x)) or X-hapten] also recognized by anti-SSEA-1 and anti-CD15. Histochemical studies with different antibodies recognizing the Lex sequence show partially overlapping patterns of immunoreactivity during early neural development in the chick embryo. Therefore, we suggest that the epitope recognized by L5 antibody is closely related to those for anti-SSEA-1 and anti-CD15.

Animals↗
PubMed1996

Roles of kringle domain-containing serine proteases in epithelial-mesenchymal transitions during embryonic development.

Transformation of an epithelial sheet into a migrating mesenchymal cell population implies the destruction of the basal lamina underlying the epithelium, and the subsequent localized digestion of the extracellular matrix by the migrating cells. Proteases are involved in these processes. Among them, molecules containing both a serine protease domain and at least one kringle domain have been identified as possible important effectors. Interestingly, related proteins containing an inactive serine protease domain also seem to play a role, suggesting that the function of these molecules in epithelial-mesenchymal transformation is not confined to proteolytic digestion of cell attachments. Instead, these molecules act through specific tyrosine kinase receptors in the membrane of the responding cells. In this review, we summarize data implicating this family of molecules in various epithelial-mesenchymal transitions during embryonic development. Our major focus of attention are: hepatocyte growth factor/scatter factor (HGF/SF), its tyrosine kinase receptor proto-oncogene c-met, and the related peptide factor HGF-like/macrophage-stimulating protein (HGF1/MSP), whose receptor is the Ron tyrosine kinase. c-met and Ron also have another close homolog in the chick, called Sea, whose ligand remains unknown. Interestingly, HGF/SF is activated by other plasminogen-related molecules which, apart from a specific activator, include the protease urokinase. HGF/SF, c-met and HGF/MSP are expressed in dynamic ways during early embryonic development, correlating with regions undergoing epithelial/mesenchymal transformations. Moreover, several assays are now starting to reveal great pleiotropism of function during development, including both the loss and the acquisition of epithelial morphology according to the cell type and assay used, as well as angiogenesis, kidney tubule morphogenesis, cell motility, the maintenance of competence for neural induction and some aspects of the later development of the musculoskeletal and nervous systems.

Animals↗
PubMed1996

Restoration of the organizer after radical ablation of Hensen's node and the anterior primitive streak in the chick embryo.

The region of the amniote embryo corresponding to Spemann's organizer in amphibians is Hensen's node, which lies at the tip of the primitive streak during gastrulation. It is a special site in the embryo that can be defined by the presence of progenitors of several axial tissues (notochord, prechordal mesoderm, somites, gut endoderm), by characteristic cell movements, by specific patterns of gene expression (e.g. goosecoid, HNF-3beta, Sonic hedgehog) and, most importantly, by its ability to induce a complete axis, including host-derived neural tissue, when transplanted to an ectopic site. Here, we show that complete removal not only of the node but also of the anterior 40% of the primitive streak leads to the development of normal embryos containing cells with all the fates normally produced by the node. Cell movement pathways through the regenerated node are identical to those seen in the normal embryo. The patterns of expression of HNF-3beta and Sonic hedgehog are also restored, as is their left/right asymmetry, but goosecoid expression is not. When the regenerated node is transplanted to an ectopic site, it induces a complete embryonic axis that includes a fully patterned, host-derived central nervous system. Analysis of the properties of cells surrounding the site of ablation shows that they acquire these properties gradually. We suggest that the organizer is a region of the embryo that is defined by cell interactions and that the node normally inhibits the organizer state in neighbouring cells.

Animals↗
PubMed1996

Fates and migratory routes of primitive streak cells in the chick embryo.

We have used carbocyanine dyes to fate map the primitive streak in the early chick embryo, from stages 3+ (mid-primitive streak) to 9 (8 somites). We show that presumptive notochord, foregut and medial somite do not originate solely from Hensen's node, but also from the anterior primitive streak. At early stages (4- and 4), there is no correlation between specific anteroposterior levels of the primitive streak and the final position of their descendants in the notochord. We describe in detail the contribution of specific levels of the primitive streak to the medial and lateral halves of the somites. To understand how the descendants of labelled cells reach their destinations in different tissues, we have followed the movement of labelled cells during their emigration from the primitive streak in living embryos, and find that cells destined to different structures follow defined pathways of movement, even if they arise from similar positions in the streak. Somite and notochord precursors migrate anteriorly within the streak and pass through different portions of the node; this provides an explanation for the segregation of notochord and somite territories in the node.

Animals↗
PubMed1995

A molecular pathway determining left-right asymmetry in chick embryogenesis.

While significant progress has been made in understanding the molecular events underlying the early specification of the antero-posterior and dorso-ventral axes, little information is available regarding the cellular or molecular basis for left-right (LR) differences in animal morphogenesis. We describe the expression patterns of three genes involved in LR determination in chick embryos: activin receptor IIa, Sonic hedgehog (Shh), and cNR-1 (related to the mouse gene nodal). These genes are expressed asymmetrically during and after gastrulation and regulate the expression of one another in a sequential pathway. Moreover, manipulation of the sidedness of either activin protein or Shh expression alters heart situs. Together, these observations identify a cascade of molecular asymmetry in that determines morphological LR asymmetry in the chick embryo.

Activins↗
PubMed1995

Expression of HGF/SF, HGF1/MSP, and c-met suggests new functions during early chick development.

We report the cloning of fulllength cDNAs for a plasminogen-related growth factor, hepatocyte growth factor/scatter factor (HGF/SF), its tyrosine kinase receptor, c-met, and a close member of the same family, hepatocyte growth factor-like/macrophage stimulating protein (HGF1/MSP), from the chick. We have used these cDNAs to provide the first report of the expression of this family of growth factors and the c-met receptor at early stages of vertebrate development. RNAase protection and wholemount in situ hybridization were used on chick embryos between formation of the primitive streak and early organogenesis. We find patterns of expression for HGF/SF and its receptor c-met consistent with their known roles in epithelial-mesenchymal transformation and angiogenesis. In addition, these genes and HGF1/MSP are expressed in discrete locations within developing somites, suggesting a role in paraxial mesodermal development. Very strong and early expression of HGF/SF in the elevating limb buds suggests its involvement in limb outgrowth. HGF1/MSP is expressed in the notochord and then in the prospective floor plate region and could play a role in development of the neural tube. Interestingly, c-met is often more closely associated with HGF1/MSP than with its known ligand, HGF/SF, raising the possibility that c-met expression may be induced by HGF1/MSP.

Amino Acid Sequence↗
PubMed1995

Activin and its receptors during gastrulation and the later phases of mesoderm development in the chick embryo.

We have cloned chick homologues of the type-II activin receptor, which we have designated cActR-IIA and -IIB. Binding assays show that the two receptors are indistinguishable in their ability to bind activin-A, with comparable kds. Injection of mRNAs encoding these receptors into Xenopus embryos causes axial duplications. Expression of both receptors can first be detected in the primitive streak by in situ hybridization. This suggests that these genes may be activated in response to mesoderm induction. In agreement with this, we find that treatment of preprimitive streak chick embryos with activin-A leads to rapid induction of the expression of cActR-IIB. At later stages, cActR-IIA transcripts become localized mainly in the notochord and myotome and cActR-IIB in the dorsal neural tube, proximal-anterior part of the limb bud, sensory placodes, and specific regions of the fore- and midbrain. To test the response of early chick embryonic tissues to activin, we designed a new in vitro assay for differentiation. We find that explants of area opaca epiblast or posterior primitive streak from various stages can respond to activin treatment by differentiating into a variety of mesodermal cell types in a dose-dependent manner. These results suggest that the importance of activin-related signaling pathways is not confined to pregastrulation stages and that these receptors may be involved in mediating the effects of inducing signals during later stages of development of the mesoderm, limbs, and nervous system.

Activin Receptors↗
PubMed1995

Neural induction and regionalisation by different subpopulations of cells in Hensen's node.

Cell lineage analysis has revealed that the amniote organizer, Hensen's node, is subdivided into distinct regions, each containing a characteristic subpopulation of cells with defined fates. Here, we address the question of whether the inducing and regionalising ability of Hensen's node is associated with a specific subpopulation. Quail explants from Hensen's node are grafted into an extraembryonic site in a host chick embryo allowing host- and donor-derived cells to be distinguished. Cell-type- and region-specific markers are used to assess the fates of the mesodermal and neural cells that develop. We find that neural inducing ability is localised in the epiblast layer and the mesendoderm (deep portion) of the medial sector of the node. The deep portion of the posterolateral part of the node does not have neural inducing ability. Neural induction also correlates with the presence of particular prospective cell types in our grafts: chordamesoderm (notochord/head process), definitive (gut) endoderm or neural tissue. However, only grafts that include the epiblast layer of the node induce neural tissue expressing a complete range of anteroposterior characteristics, although prospective prechordal plate cells may also play a role in specification of the forebrain.

Animals↗
PubMed1995

A role for HGF/SF in neural induction and its expression in Hensen's node during gastrulation.

It was previously shown (Roberts, C., Platt, N., Streit, A., Schachner, M. and Stern, C. D. (1991) Development 112, 959-970) that grafts of Hensen's node into chick embryos enhanced and maintain expression of the L5 carbohydrate in neighbouring epiblast cells, and that antibodies against L5 inhibit neural induction by such a graft. We now show that L5 is initially widely expressed in the epiblast, but as neural induction proceeds it gradually becomes confined to and up-regulated in the early neural plate. L5 can therefore be considered as a marker for cells that are competent to respond to neural induction. We also show that Hepatocyte Growth Factor/Scatter Factor (HGF/SF) promotes the expression of L5 by extraembryonic epiblast in collagen gels after overnight culture. Explants cultured for several days in the presence of HGF/SF, as well as explants of prospective neural plate, can differentiate into cells with neuronal morphology expressing neuronal markers. To investigate whether HGF/SF is expressed in the chick embryo at appropriate stages of development, we produced specific cDNA probes and used them for in situ hybridization. We find that at the primitive streak stage, HGF/SF is expressed specifically in Hensen's node. We therefore propose that HGF/SF plays a role during the early steps of neural induction, perhaps by inducing or maintaining the competence of the epiblast to respond to neural inducing signals.

Animals↗
PubMed1995

Common molecular pathways for patterning of the body axis, limbs, central nervous system, and face during embryonic development.

Many congenital anomalies affecting the face are known to appear as syndromes or associations, in combination with other defects. Often, these involve the limbs, eyes, central nervous system, and body axis. A general, and understandable, tendency among clinical researchers has been to seek a single cell type or definable embryologic process on which to ascribe the etiologic basis for such associations. The possibility of a gene, or group of genes, under coordinate control has not received much attention until recently. With the advent of recombinant DNA technology and the current explosion in basic research on the molecular bases of embryonic development, however, several possibilities are beginning to emerge. Here, I will list a few genes whose expression during development suggests that the molecules they encode are used as part of a coordinate molecular pathway, and that they play a role in the development of systems that often appear together in congenital associations or syndromes.

Abnormalities, Multiple↗
PubMed1994

The avian embryo: a powerful model system for studying neural induction.

Neural induction is the process during early embryonic development whereby the mesoderm of the embryo elicits a change of fate in cells of the overlying ectoderm, from epidermal to neural. Since its discovery in 1924 by Spemann and Mangold, who used newt embryos, most research on this developmental event has been conducted with urodelean and anuran amphibians. This is because of the ease with which they can be manipulated and because of the recent availability of cell type- and region-specific molecular markers. With the recent isolation and characterization of suitable markers in the chick embryo, and the equal ease with which it can be manipulated, the way is now open for amniote embryos to join amphibians as an experimental system for neural induction studies. Another advantage of the avian embryo is that it possesses a peripheral extraembryonic region, which although it does not contribute to embryonic tissues at all, is competent to respond to neural-inducing signals, thereby providing developmentally naive cells for in vivo and in vitro assays. Here, I review recent advances that make the chick embryo a system uniquely suited for the study of neural induction at both the cellular and the molecular level.

Animals↗
PubMed1994

A fate map of the epiblast of the early chick embryo.

We have used carbocyanine dyes (DiI and DiO) to generate fate maps for the epiblast layer of the chick embryo between stage X and the early primitive streak stage (stages 2-3). The overall distribution of presumptive cell types in these maps is similar to that described for other laboratory species (zebrafish, frog, mouse). Our maps also reveal certain patterns of movement for these presumptive areas. Most areas converge towards the midline and then move anteriorly along it. Interestingly, however, some presumptive tissue types do not take part in these predominant movements, but behave in a different way, even if enclosed within an area that does undergo medial convergence and anterior movement. The apparently independent behaviour of certain cell populations suggests that at least some presumptive cell types within the epiblast are already specified at preprimitive streak stages.

Animals↗
PubMed1993

The homeobox gene goosecoid and the origin of organizer cells in the early chick blastoderm.

The chick homeobox gene goosecoid (gsc) is first expressed in a barely noticeable cell population near the posterior margin (Koller's sickle) of the unincubated egg. Then it is detected in Hensen's node, traditionally considered the chick organizer. Later, gsc-expressing cells leave the node with the prechordal plate. Fate mapping indicates that these three regions are related by cell lineage, and transplantation experiments suggest that they all have inducing activity. Quail posterior margin and anterior primitive streak grafts (gsc expressing) induce gsc transcription in neighboring chick host cells. We propose that development of the chick organizer starts earlier than previously thought and that gsc marks this changing cell population.

Amino Acid Sequence↗
PubMed1993

Segmental organization of embryonic diencephalon.

The diencephalon is a complex integration centre and intricate relay station of the vertebrate brain. Its development involves the generation of great cellular diversity and neuronal specificity. We report here that it becomes organized in steps, through a stereotyped sequence of neuromeric subdivisions. Diencephalic neuromeres define four cellular domains (D1-D4) that can be followed throughout development, each unit contributing to a well defined part of the adult structural pattern. We propose that the segmental identity of each diencephalic unit is specified by a unique combination of genes, maintained by polyclonal cell lineage restrictions. A comparison of vertebrate and arthropod development suggests that the basic principles that control anterior axial patterning and set up neuronal specificity in the embryonic central nervous system are highly conserved in evolution.

Acetylcholinesterase↗
PubMed1993

HGF-SF: a neural inducing molecule in vertebrate embryos?

Neural induction is the process, during early embryonic development, by which cells of the mesoderm cause the overlying ectoderm cells to differentiate into neural structures, rather than epidermis. The phenomenon was discovered over 80 years ago in Hans Spemann's laboratory, and has since attracted much interest. However, we are still ignorant about the signals that elicit such a change in the direction of ectodermal differentiation, and about the mechanisms involved in the response of the ectoderm. Here, we report that HGF-SF can cause cultured chick ectodermal cells to become neural. We also discuss preliminary evidence suggesting that a homolog of this factor is expressed in Hensen's node, the inducing tissue, at about the stage at which neural induction occurs. We speculate that HGF-SF, or a related factor, could be a neural inducing signal during the early development of vertebrate embryos.

Animals↗