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C D Stern

Publications and source records attributed to C D Stern.

At least 19 recordsLinked to original sources
PubMed1992

Mesoderm induction and development of the embryonic axis in amniotes.

The mechanisms controlling the formation of the embryonic axis, and specifically those that give rise to the mesoderm, have received renewed attention recently. In the frog, some of these mechanisms have begun to be elucidated, and several factors have been found to cause uncommitted ectoderm cells to differentiate into mesoderm. All of the factors identified to date are related either to fibroblast growth factor (FGF) or to transforming growth factor beta (TGF-beta). Do the mechanisms that generate the embryonic axis of amphibians also operate in chick and mouse embryos? Here I address how amphibian and amniote embryos might provide complementary pieces of a puzzle.

Amphibians↗
PubMed1992

Vertebrate gastrulation.

Our understanding of the mechanisms that control gastrulation is still in its infancy. One problem is that gastrulation is a complex set of coordinated behaviours involving directional cell movements, several types of cell interactions, changes in cell fate and gene expression. Therefore, the successful analysis of its control mechanisms requires simultaneous analysis of more than one of these, or at least some way of separating them. Although progress has been slow, some recent studies have made significant advances in the field and we can probably look forward to some major breakthroughs in the near future.

Animals↗
PubMed1992

Neural induction and regionalisation in the chick embryo.

Induction and regionalisation of the chick nervous system were investigated by transplanting Hensen's node into the extra-embryonic region (area opaca margin) of a host embryo. Chick/quail chimaeras were used to determine the contributions of host and donor tissue to the supernumerary axis, and three molecular markers, Engrailed, neurofilaments (antibody 3A10) and XlHbox1/Hox3.3 were used to aid the identification of particular regions of the ectopic axis. We find that the age of the node determines the regions of the nervous system that form: young nodes (stages 2-4) induced both anterior and posterior nervous system, while older nodes (stages 5-6) have reduced inducing ability and generate only posterior nervous system. By varying the age of the host embryo, we show that the competence of the epiblast to respond to neural induction declines after stage 4. We conclude that during normal development, the initial steps of neural induction take place before stage 4 and that anteroposterior regionalisation of the nervous system may be a later process, perhaps associated with the differentiating notochord. We also speculate that the mechanisms responsible for induction of head CNS differ from those that generate the spinal cord: the trunk CNS could arise by homeogenetic induction by anterior CNS or by elongation of neural primordia that are induced very early.

Animals↗
PubMed1992

Relationships between mesoderm induction and the embryonic axes in chick and frog embryos.

The hypoblast is generally thought to be responsible for inducing the mesoderm in the chick embryo because the primitive streak, and subsequently the embryonic axis, form according to the orientation of the hypoblast. However, some cells become specified as embryonic mesoderm very late in development, towards the end of the gastrulation period and long after the hypoblast has left the embryonic region. We argue that induction of embryonic mesoderm and of the embryonic axis are different and separable events, both in amniotes and in amphibians. We also consider the relationships between the dorsoventral and anteroposterior axes in both groups of vertebrates.

Animals↗
PubMed1991

Fate mapping and cell lineage analysis of Hensen's node in the chick embryo.

Fate maps of chick Hensen's node were generated using DiI and the lineage of individual cells studied by intracellular injection of lysine-rhodamine-dextran (LRD). The cell types contained within the node are organized both spatially and temporally. At the definitive primitive streak stage (Hamburger and Hamilton stage 4), Hensen's node contains presumptive notochord cells mainly in its anterior midline and presumptive somite cells in more lateral regions. Early in development it also contains presumptive endoderm cells. At all stages studied (stages 3-9), some individual cells contribute progeny to more than one of these tissues. The somitic precursors in Hensen's node only contribute to the medial halves of the somites. The lateral halves of the somites are derived from a separate region in the primitive streak, caudal to Hensen's node.

Animals↗
PubMed1991

The L5 epitope: an early marker for neural induction in the chick embryo and its involvement in inductive interactions.

The pattern of expression of the carbohydrate epitope L5 was studied during early development of the chick neuroepithelium. Immunoreactivity first appears during gastrulation, at mid-primitive streak stage, and persists until at least 3.5 days of development. The epitope is expressed on all the components of the developing nervous system, both central and peripheral. In immunoblots, the antibody recognises a major component of about Mr 500,000 and several more minor components of lower molecular mass. If a Hensen's node from a donor embryo is transplanted into the area opaca of a host embryo, L5 immunoreactivity appears in the epiblast surrounding the graft. If hybridoma cells secreting the antibody are grafted together with Hensen's node into a host chick embryo, the induction of a supernumerary nervous system is inhibited. We suggest that the L5 epitope is an early and general marker for neural induction and that it may be involved directly in inductive interactions.

Animals↗
PubMed1991

Tissue interactions affecting the migration and differentiation of neural crest cells in the chick embryo.

A series of microsurgical operations was performed in chick embryos to study the factors that control the polarity, position and differentiation of the sympathetic and dorsal root ganglion cells developing from the neural crest. The neural tube, with or without the notochord, was rotated by 180 degrees dorsoventrally to cause the neural crest cells to emerge ventrally. In some embryos, the notochord was ablated, and in others a second notochord was implanted. Sympathetic differentiation was assessed by catecholamine fluorescence after aldehyde fixation. Neural crest cells emerging from an inverted neural tube migrate in a ventral-to-dorsal direction through the sclerotome, where they become segmented by being restricted to the rostral half of each sclerotome. Both motor axons and neural crest cells avoid the notochord and the extracellular matrix that surrounds it, but motor axons appear also to be attracted to the notochord until they reach its immediate vicinity. The dorsal root ganglia always form adjacent to the neural tube and their dorsoventral orientation follows the direction of migration of the neural crest cells. Differentiation of catecholaminergic cells only occurs near the aorta/mesonephros and in addition requires the proximity of either the ventral neural tube (floor plate/ventral root region) or the notochord. Prior migration of presumptive catecholaminergic cells through the sclerotome, however, is neither required nor sufficient for their adrenergic differentiation.

Animals↗
PubMed1991

An evaluation of myelomeres and segmentation of the chick embryo spinal cord.

We have investigated whether the neuromeres of the developing chick spinal cord (myelomeres) are manifestations of intrinsic segmentation of the CNS by studying the patterns of cell proliferation and neuronal differentiation. Treatment of 2-day embryos with colchicine does produce exaggerated myelomeres, in confirmation of Källén (Z. Anat. Entwickl.-Gesch. 123, 309-319, 1962). However, this does not imply that myelomeres are segmental proliferation centres: the undulations caused by colchicine are irregular alongside the unsegmented mesoderm, and another mitotic inhibitor, bromodeoxyuridine, has no such effects. In contrast to lower vertebrate embryos, there is no evidence for segmental groups of primary motor neurons in the chick: the earliest motor neurons express cholinesterase, and project their axons into the adjacent sclerotome, at random positions in relation to the somite boundaries. The population of motor neurons projecting HRP-labelled axons into a single somite lies out of phase with both myelomere and somite, and is placed symmetrically about the anterior half-sclerotome. The earliest intrinsic spinal cord neurons, as stained with zinc iodide-osmium tetroxide or anti-68 x Mr neurofilament antibody, show no segmental patterns of differentiation. We conclude that, in contrast to the rhombomeres of the developing hindbrain, myelomeres are not matched by segmental groupings of differentiating nerve cells, and result from mechanical moulding of the neuroepithelium by the neighbouring somites.

Animals↗
PubMed1991

Segmental lineage restrictions in the chick embryo spinal cord depend on the adjacent somites.

We have investigated whether the developing spinal cord is intrinsically segmented in its rostrocaudal (anteroposterior) axis by mapping the spread of clones derived from single labelled cells within the neural tube of the chick embryo. A single cell in the ventrolateral neural tube of the trunk was marked in situ with the fluorescent tracer lysinated rhodamine dextran (LRD) and its descendants located after two days of further incubation. We find that clones derived from cells labelled before overt segmentation of the adjacent mesoderm do not respect any boundaries within the neural tube. Those derived from cells marked after mesodermal segmentation, however, never cross an invisible boundary aligned with the middle of each somite, and tend to be elongated along the mediolateral axis of the neural tube. When the somite pattern is surgically disturbed, neighbouring clones derived from neuroectodermal cells labelled after somite formation behave like clones derived from younger cells: they no longer respect any boundaries, and are not elongated mediolaterally. These results indicate that periodic lineage restrictions do exist in the developing spinal cord of the chick embryo, but their maintenance requires the presence of the adjacent somite mesoderm.

Animals↗
PubMed1990

Origin of cells giving rise to mesoderm and endoderm in chick embryo.

In amniotes, all of the tissues of the adult arise from the epiblast, one of the two layers of cells present in the early embryo; the mesoderm and gut endoderm arise from an epiblast-derived structure known as the primitive streak. The monoclonal antibody HNK-1 recognizes the cells of the primitive streak in the chick embryo. Before streak formation, HNK-1 identifies cells that are randomly distributed within the epiblast. We have now used two novel ways to study cell lineage and commitment to show that the epiblast of the early chick embryo contains two distinct populations of cells with different developmental fates at a stage during which 'mesodermal induction' is believed to occur. One cell population, recognized by monoclonal antibody HNK-1, is destined to form mesoderm and endoderm; the rest of the epiblast is unable to give rise to mesoderm if this population of cells is removed.

Animals↗
PubMed1990

Isolation from chick somites of a glycoprotein fraction that causes collapse of dorsal root ganglion growth cones.

The segmented pattern of peripheral spinal nerves in higher vertebrates is generated by interactions between nerve cells and somites. Neural crest cells, motor axons, and sensory axons grow exclusively through anterior-half sclerotome. In chick embryos, posterior cells bind the lectins peanut agglutinin (PNA) and Jacalin. When liposomes containing somite extracts are applied to cultures of chick sensory neurons, growth cones collapse abruptly, recovering within 4 hr of liposome removal. Collapse activity is eliminated by immobilized PNA, and SDS-PAGE demonstrates two major components (48K and 55K), which are absent from anterior-half sclerotome. Rabbit polyclonal antibodies against these components recognize only posterior cells and may also be used to eliminate collapse activity. We suggest that spinal nerve segmentation is produced by inhibitory interactions between these components and growth cones.

Animals↗
PubMed1990

The marginal zone and its contribution to the hypoblast and primitive streak of the chick embryo.

The marginal zone of the chick embryo has been shown to play an important role in the formation of the hypoblast and of the primitive streak. In this study, time-lapse filming, fate mapping, ablation and transplantation experiments were combined to study its contribution to these structures. It was found that the deep (endodermal) portion of the posterior marginal zone contributes to the hypoblast and to the junctional endoblast, while the epiblast portion of the same region contributes to the epiblast of the primitive streak and to the definitive (gut) endoderm derived from it. Within the deep part of the posterior marginal zone, a subpopulation of HNK-1-positive cells contributes to the hypoblast. Removal of the deep part of the marginal zone prevents regeneration of the hypoblast but not the formation of a primitive streak. Removal of both layers of the marginal zone leads to a primitive streak of abnormal morphology but mesendodermal cells nevertheless differentiate. These results show that the two main properties of the posterior marginal zone (contributing to the hypoblast and controlling the site of primitive streak formation) are separable, and reside in different germ layers. This conclusion does not support the idea that the influence of the posterior marginal zone on the development of axial structures is due to it being the source of secondary hypoblast cells.

Animals↗
PubMed1990

Epithelial scatter factor and development of the chick embryonic axis.

Scatter factor, a recently characterised protein secreted by certain embryonic fibroblasts, affects cultured epithelial by increasing cell motility, the breakdown of cell junctions and cell scattering. The process of gastrulation in higher vertebrate embryos, during which the primitive streak forms, involves an epithelial-to-mesenchymal transformation resembling the effects of the factor on cultured cells. The factor was applied locally to chick embryos, using both scatter-factor-secreting cell lines and inert carriers. We found that scatter factor can generate local supernumerary axial structures resembling primitive streak and/or neural plate and conclude that it may have primitive-streak and/or neural-inducing activity in chick embryos.

Animals↗
PubMed1989

Comparative carcinogenicity of the PAHs as a basis for acceptable exposure levels (AELs) in drinking water.

The carcinogenicity of various polynuclear aromatic hydrocarbons (PAHs) has generally been demonstrated by their ability to act as complete carcinogens in the development of cancers in rodent skin tests. In order to develop proposed acceptable concentration levels for various PAHs in drinking water, we reviewed the studies that formed the basis for determining that these specific PAHs were carcinogenic in animals. We found that the relative potency of these PAHs varied over a range of many orders of magnitude. For example, the carcinogenic strength of benz[a]anthracene (BaA) is found to be about 1/2000th that of benzo[a]pyrene (BaP). We have used the calculated carcinogenic potency of the various PAHs relative to that of BaP as a means for proposing specific acceptable concentration levels in drinking water for each of the specific PAHs. BaP is the only carcinogenic PAH for which EPA has published an acceptable concentration level based on carcinogenicity. Based on the level EPA set for BaP (0.028 micrograms/liter), this methodology has provided for the specific PAHs a determination of proposed acceptable concentration levels quantitatively based on the same data that were used to qualitatively determine them to be animal carcinogens. We have proposed acceptable concentration levels for the carcinogenic PAHs in drinking water that range from 0.03 micrograms/liter for BaP to 6.5 micrograms/liter for BaA. We recommend that acceptable concentration levels for the various PAHs be based on their relative carcinogenic potencies rather than the EPA method of using the potency of only one specific PAH, BaP, to serve as the exposure level determinant for all PAHs. We further suggest that this methodology may be applicable to other classes of carcinogenic compounds. We have also found useful for the determination of acceptable concentration levels for the noncarcinogenic PAHs an analogous methodology based on the relative toxicities of the noncarcinogenic PAHs.

Animals↗
PubMed1989

Periodic segmental anomalies induced by heat shock in the chick embryo are associated with the cell cycle.

This study provides evidence that cells destined to segment together into somites have a degree of cell division synchrony. We have measured the duration of the cell division cycle in somite and segmental plate cells of the chick embryo as 9.5 h using [3H]thymidine pulse- and-chase. Treatment of embryos with any of a variety of inhibitors known to affect the cell division cycle causes discrete periodic segmental anomalies: these anomalies appear about 6-7 somites after treatment and, in some cases, a second anomaly is observed 6 to 7 somites after the first. Since somites take 1.5 h to form, the 6- to 7- somite interval corresponds to about 9-10 h, which is the duration of the cell cycle as determined in these experiments. The anomalies are similar to those seen after heat shock of 2-day chick embryos. Heat shock and some of the other treatments induce the expression of heat-shock proteins (hsp); however, since neither the expression nor the distribution of these proteins relate to the presence or distribution of anomalies seen, we conclude that hsps are not responsible for the pattern of segmental anomalies observed. The production of periodic segmental anomalies appears to be linked to the cell cycle. A simple model is proposed, in which we suggest that the cell division cycle is involved directly in gating cells that will segment together.

Animals↗
PubMed1989

Molecular differences between the rostral and caudal halves of the sclerotome in the chick embryo.

It is known that both neural crest cell migration and motor axon outgrowth in most vertebrate embryos are segmented because of restrictions imposed upon their distribution by the neighbouring sclerotomes, each of which is divided into a rostral and a caudal half. The caudal half does not allow crest migration or axon outgrowth, while the rostral half does. In this paper, we investigate the expression of proteins and glycoproteins in the two halves of the sclerotome of the chick embryo at stages between 20 and 32 pairs of somites by two-dimensional SDS-polyacrylamide gel electrophoresis. We find that the patterns of expression are complex, and that polypeptides and glycoproteins vary both spatially and temporally: of those that are expressed differentially by the sclerotome, some differ quantitatively and others qualitatively. Some macromolecules change their spatial distribution with developmental age, and some appear or disappear as the embryos become older.

Animals↗
PubMed1989

J1/tenascin-related molecules are not responsible for the segmented pattern of neural crest cells or motor axons in the chick embryo.

It has been suggested that substrate adhesion molecules of the tenascin family may be responsible for the segmented outgrowth of motor axons and neural crest cells during formation of the peripheral nervous system. We have used two monoclonal antibodies (M1B4 and 578) and an antiserum [KAF9(1)] to study the expression of J1/tenascin-related molecules within the somites of the chick embryo. Neural crest cells were identified with monoclonal antibodies HNK-1 and 20B4. Young somites are surrounded by J1/tenascin immunoreactive material, while old sclerotomes are immunoreactive predominantly in their rostral halves, as described by other authors (Tan et al. 1987--Proc. natn. Acad. Sci. U.S.A. 84, 7977; Mackie et al. 1988--Development 102, 237). At intermediate stages of development, however, immunoreactivity is found mainly in the caudal half of each sclerotome. After ablation of the neural crest, the pattern of immunoreactivity is no longer localised to the rostral halves of the older, neural-crest-free sclerotomes. SDS-polyacrylamide gel electrophoresis of affinity-purified somite tissue, extracted using M1B4 antibody, shows a characteristic set of bands, including one of about 230 x 10(3), as described for cytotactin, J1-200/220 and the monomeric form of tenascin. Affinity-purified somite material obtained from neural-crest-ablated somites reveals some of the bands seen in older control embryos, but the high molecular weight components (120-230 x 10(3] are missing. Young epithelial somites also lack the higher molecular mass components. The neural crest may therefore participate in the expression of J1/tenascin-related molecules in the chick embryo. These results suggest that these molecules are not directly responsible for the segmented outgrowth of precursors of the peripheral nervous system.

Animals↗