Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Embryonic Induction”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 865 records · Page 48Linked to original sources
PubMed1994

Hypoblastic tissue and fibroblast growth factor induce blood tissue (haemoglobin) in the early chick embryo.

We have investigated the temporal and the causal basis of blood tissue specification in the chick embryo. Earlier workers have shown that the prospective blood-forming area is specified in a horseshoe-shaped area at the posterior side of the embryo. We found that cultured explants from the posterior marginal zone at stages XI to XIII (consisting of the posterior marginal zone and part of Koller's sickle) have a high propensity to form haemoglobin (Hb), which could be inhibited at stage XI by adding antibody against basic fibroblast growth factor (bFGF) to the neutral culture medium; this treatment had no effect from stage XII onwards. The same result was found when whole embryos were cultured with an antiserum raised against bFGF, or with heparin. In another series of experiments, we found that cultured pieces from the inner-core of stage XIII epiblasts (with or without hypoblast tissue) were able to form Hb, whereas inner-core pieces from the pre-hypoblast stages, namely stages X and XI, did not form Hb. The capacity to form Hb, however, could be conferred upon the inner-core pieces from stage X epiblasts if bFGF at a concentration of 75-150 ng/ml was added to the culture medium. Furthermore, and most pertinently, the capacity to form Hb could be conferred on stage X inner-core pieces when they were co-cultured with hypoblast from a stage XIII embryo in a sandwich explant. Thus the inductive role of the hypoblast appears to be mediated via bFGF.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1980

Prostatic induction: interaction of epithelium and mesenchyme from normal wild-type mice and androgen-insensitive mice with testicular feminization.

The prostate gland develops from the urogenital sinus as epithelial buds projecting into the surrounding mesenchyme. The role of the mesenchyme in this process was determined using sinuses from normal and androgen-insensitive Tfm mice which are deficient in androgen receptors. Epithelium and mesenchyme from both types of sinus were separated and recombined and the recombinants grown in organ culture in the presence of testosterone. Recombinants consisting of normal epithelium and normal mesenchyme developed epithelial buds projecting into the surrounding mesenchyme but no buds were formed in recombinants of epithelium and mesenchyme from mutant mice. In recombinants of epithelium from mutant mice with normal mesenchyme the epithelium developed prostatic buds and the number was similar to that found if normal epithelium was associated with normal mesenchyme. In contrast, normal epithelium combined with mesenchyme from mutant mice failed to form prostatic buds. The results suggested that the mesenchyme determines the development of prostatic buds and that the lack of inductive capacity of the mesenchyme from mutant mice may be due to a deficiency of mesenchymal androgen receptors.

Androgen-Insensitivity Syndrome↗
PubMedDate not supplied

Increasing potentiality in N.G.F. treated PC12 cells.

Somites from 9H. H. chick embryos and PC12 cells were co-cultivated in synthetic medium containing N.G.F., which induces the transformation of PC12 cells into neuron-like cells. During the first two days of culture, PC12 cells retained the spherical shape and tended to cluster. Somitic mesoderm cells exhibited a fibroblastic aspect. By the third day, PC12 cells extended long processes resembling nerve fibres which surrounded and penetrated the mesodermic explants. On the 10th day of culture, contractions, limited at first to a few cells were perceptible. Later, the contractions involved large cellular masses. Microscopic observations at 10 days revealed the presence of an increasing number of fusiform mononucleated cells. Later, long and narrow multinucleated elements appeared. Such elements never developed from cultures of only somites. Immunohistochemical observations revealed a desmin positivity in both mononucleated and multinucleated elements characterizing them as myogenic cells that are formed in and because of the presence of PC12 cells which were transformed by N.G.F. into nerve cells. After 10 days of culture, PC12 cells positive to antiserum antidesmin were noted. Desmin positivity of PC12 cells leads to the conclusion that newly-formed muscle cells exert an induction on Pheocromocytoma cells which, as derivatives of the neural crest, have a greater multipotentiality.

Animals↗
PubMed1993

Gene activation in response to neural induction.

In order to study the molecular processes involved in the final steps of neural induction, we are investigating the transcriptional regulation of the Xenopus laevis neural cell adhesion molecule (NCAM) gene. NCAM is expressed very early during neural development and its expression is dependent on neural induction signals. Using microinjection of reporter gene constructions into fertilized frog eggs, we have shown that cloned copies of the NCAM promoter respond appropriately to neural induction signals. Examination of the Xenopus NCAM promoter reveals a number of potential regulatory elements. We have directed our attention to a small region of the promoter that is highly conserved over large evolutionary distances. This region contains an enhancer, the OZ element, and also a silencer element, the N-box. We have purified DNA DNA proteins that interact specifically with both the OZ enhancer and the N-box silencer sequences. A model suggesting a role for these regulatory factors during neural induction is presented.

Animals↗
PubMed2003

The proliferative state, graft-site and contact-time of competent chick ectoblast determine the quality and quantity of neural induction by Hensen's node.

We have assessed the type and amount of neural tissue induced in the chick gastrula ectoblast with increasing duration of contact with the Hensen node inducer. At least 4 h contact is necessary to induce the ectoblast in the area pellucida, 9 h in the area opaca and even longer at the margin of overgrowth. In the area pellucida, the inductive response shifts from archencephalic type at 4-6 h contact to deuterencephalic type after 9 h contact. The induced tissue volume and cell number increased as graft-host contact increased from 4-9 h, and then decreased with longer contact. We suggest that in addition to the period of contact and the grafting position on competent ectoblast, the rate of cell proliferation may control the axial specificity and morphological organization of the induced neural tissue.

Animals↗
PubMed1996

Local delivery of TGF beta2 can substitute for placode epithelium to induce mesenchymal condensation during skin appendage morphogenesis.

Development of skin appendages requires interactions between the epithelium and mesenchyme. Without the epithelium, dermal condensations cannot develop, and those already formed will disintegrate. Here we explored the molecular basis of this epithelial requirement and tried to identify the molecule(s) responsible by using the chick feather bud development as a model. TGF beta2 is a likely candidate because its message is predominantly expressed in the feather bud epithelium, and the protein is enriched in the dermal-epidermal junction within the bud. We tested this hypothesis by placing TGF beta-soaked beads on skin explants. We found that TGF beta2, but not TGF beta1, beads placed on top of epithelially stripped mesenchymes can induce dermal condensations. NCAM and tenascin-C (Tn-C) are expressed and protein kinase C is suppressed in the normal feather bud domain. This molecular organization is lost in denuded mesenchyme but can be restored by TGF beta2-coated beads. Subsequently, the TGF beta2-induced dermal condensations can induce nascent epithelium to form skin appendages. Together with our recent findings that ectopic Sonic hedgehog (Shh) expression causes wider TGF beta expression and larger dermal condensation, these results strongly suggest that TGF beta2 produced by epithelial placode is downstream to Shh and plays a key role in the induction of dermal condensation by activating the expression of NCAM and Tn-C, and by suppressing PKC expression.

Animals↗
PubMed1989

Progressive determination during formation of the anteroposterior axis in Xenopus laevis.

The cement gland is an ectodermal organ in the head of frog embryos, lying anterior to any neural tissue. As analyzed by specific RNA expression, cement gland, like neural tissue, was induced by the dorsal mesoderm. Interestingly, mesoderm with the highest cement gland-inducing potential lay posterior to the ectoderm fated to form this organ, indicating that its induction occurred at a distance from the inducer source. Cement gland induction first occurred during early gastrulation. However, most initially induced cells did not contribute to the mature cement gland, but instead formed part of the neural plate. This change in fate could be reconstituted in vitro. These results suggest that determination of part of the anteroposterior axis occurs progressively, where future neural ectoderm is first induced to a cement glandlike state. As gastrulation proceeds, further induction by mesoderm may override this state, which persists only in the extreme anterior of the embryo.

Ammonium Chloride↗
PubMed1998

Neural induction in embryos.

Neural differentiation of the ectoderm is inhibited by bone morphogenetic protein 4 (BMP-4) in amphibia as well as mammalia. This inhibition is released by neural inducing factor(s), which are secreted from the dorsal mesoderm. Masked neuralizing factor(s) are already present in the ectoderm before induction. In homogenates from Xenopus oocytes and embryos neural inducing factors were found in the supernatant (centrifuged at 105000 g), in small vesicles and a ribonucleoprotein fraction. A neuralizing factor, which is a protein of small size, has been partially purified from Xenopus gastrulae. Genes that are expressed in the dorsal mesoderm and involved in the de novo synthesis of neuralizing factor(s) have been cloned. The differentiation of cells with a neuronal fate starts in the neural plate immediately after neural induction. Genes homologous to the Notch and Delta genes of lateral inhibition in insects are involved in this process.

Animals↗
PubMed2002

Activation of Wnt signaling bypasses the requirement for RTK/Ras signaling during C. elegans vulval induction.

During Caenorhabditis elegans vulval development, activation of receptor tyrosine kinase/Ras and Notch signaling pathways causes three vulval precursor cells (VPCs) to adopt induced cell fates. A Wnt signaling pathway also acts in cell fate specification by the VPCs, via regulation of the Hox gene lin-39. We show here that either mutation of pry-1 or expression of an activated BAR-1 beta-catenin protein causes an Overinduced phenotype, in which greater than three VPCs adopt induced cell fates. This indicates that pry-1, which encodes a C. elegans axin homolog, acts as a negative regulator of Wnt signaling in the VPCs. Loss of activity of the APC homolog apr-1 increases the penetrance of this Overinduced phenotype, suggesting that APR-1 may play a negative role in Wnt signaling in this process in C. elegans similar to APC proteins in other systems. The Overinduced phenotype is suppressed by reduction of function of the genes pop-1 TCF and lin-39 Hox. Surprisingly, the Overinduced phenotype caused by hyperactivated Wnt signaling is not dependent on signaling through the Ras pathway. These data suggest that hyperactivation of Wnt signaling is sufficient to cause VPCs to adopt induced fates and that a canonical Wnt pathway may play an important role during C. elegans vulval induction.

Adenomatous Polyposis Coli Protein↗
PubMed1987

Regional specification within the mesoderm of early embryos of Xenopus laevis.

We have further analysed the roles of mesoderm induction and dorsalization in the formation of a regionally specified mesoderm in early embryos of Xenopus laevis. First, we have examined the regional specificity of mesoderm induction by isolating single blastomeres from the vegetalmost tier of the 32-cell embryo and combining each with a lineage-labelled (FDA) animal blastomere tier. Whereas dorsovegetal (D1) blastomeres induce 'dorsal-type' mesoderm (notochord and muscle), laterovegetal and ventrovegetal blastomeres (D2-4) induce either 'intermediate-type' (muscle, mesothelium, mesenchyme and blood) or 'ventral-type' (mesothelium, mesenchyme and blood) mesoderm. No significant difference in inductive specificity between blastomeres D2, 3 and 4 could be detected. We also show that laterovegetal and ventrovegetal blastomeres from early cleavage stages can have a dorsal inductive potency partially activated by operative procedures, resulting in the induction of intermediate-type mesoderm. Second, we have determined the state of specification of ventral blastomeres by isolating and culturing them in vitro between the 4-cell stage and the early gastrula stage. The majority of isolates from the ventral half of the embryo gave extreme ventral types of differentiation at all stages tested. Although a minority of cases formed intermediate-type and dorsal-type mesoderms we believe these to result from either errors in our assessment of the prospective DV axis or from an enhancement, provoked by microsurgery, of some dorsal inductive specificity. The results of induction and isolation experiments suggest that only two states of specification exist in the mesoderm of the pregastrula embryo, a dorsal type and a ventral type. Finally we have made a comprehensive series of combinations between different regions of the marginal zone using FDA to distinguish the components. We show that, in combination with dorsal-type mesoderm, ventral-type mesoderm becomes dorsalized to the level of intermediate-type mesoderm. Dorsal-type mesoderm is not ventralized in these combinations. Dorsalizing activity is confined to a restricted sector of the dorsal marginal zone, it is wider than the prospective notochord and seems to be graded from a high point at the dorsal midline. The results of these experiments strengthen the case for the three-signal model proposed previously, i.e. dorsal and ventral mesoderm inductions followed by dorsalization, as the simplest explanation capable of accounting for regional specification within the mesoderm of early Xenopus embryos.

Animals↗
PubMed1994

The cleavage stage origin of Spemann's Organizer: analysis of the movements of blastomere clones before and during gastrulation in Xenopus.

Recent investigations into the roles of early regulatory genes, especially those resulting from mesoderm induction or first expressed in the gastrula, reveal a need to elucidate the developmental history of the cells in which their transcripts are expressed. Although fates both of the early blastomeres and of regions of the gastrula have been mapped, the relationship between the two sets of fate maps is not clear and the clonal origin of the regions of the stage 10 embryo are not known. We mapped the positions of each blastomere clone during several late blastula and early gastrula stages to show where and when these clones move. We found that the dorsal animal clone (A1) begins to move away from the animal pole at stage 8, and the dorsal animal marginal clone (B1) leaves the animal cap by stage 9. The ventral animal clones (A4 and B4) spread into the dorsal animal cap region as the dorsal clones recede. At stage 10, the ventral animal clones extend across the entire dorsal animal cap. These changes in the blastomere constituents of the animal cap during epiboly may contribute to the changing capacity of the cap to respond to inductive growth factors. Pregastrulation movements of clones also result in the B1 clone occupying the vegetal marginal zone to become the primary progenitor of the dorsal lip of the blastopore (Spemann's Organizer). This report provides the fundamental descriptions of clone locations during the important periods of axis formation, mesoderm induction and neural induction. These will be useful for the correct targeting of genetic manipulations of early regulatory events.

Animals↗
PubMed1992

Muscle gene activation in Xenopus requires intercellular communication during gastrula as well as blastula stages.

In Xenopus an early morphological marker of mesodermal induction is the elongation of the mesoderm at the early gastrula stage (Symes and Smith, 1987). We show here that the elongation of equatorial (marginal) tissue is dependent on protein synthesis in a mid blastula, but has become independent of it by the late blastula stage. In animal caps induced to become mesoderm, the time when protein synthesis is required for subsequent elongation immediately follows the time of induction, and is not related to developmental stage. For elongation, intercellular communication during the blastula stage is of primary importance. Current experiments involving cell transplantation indicate a need for further cell:cell interactions during gastrulation, and therefore after the vegetal-animal induction during blastula stages. These secondary cell interactions are believed to take place among cells that have already received a vegetal induction, and may facilitate some of the later intracellular events known to accompany muscle gene activation.

Animals↗
PubMed2003

Distinct modes of floor plate induction in the chick embryo.

To begin to reconcile models of floor plate formation in the vertebrate neural tube, we have performed experiments aimed at understanding the development of the early floor plate in the chick embryo. Using real-time analyses of cell behaviour, we provide evidence that the principal contributor to the early neural midline, the future anterior floor plate, exists as a separate population of floor plate precursor cells in the epiblast of the gastrula stage embryo, and does not share a lineage with axial mesoderm. Analysis of the tissue interactions associated with differentiation of these cells to a floor plate fate reveals a role for the nascent prechordal mesoderm, indicating that more than one inductive event is associated with floor plate formation along the length of the neuraxis. We show that Nr1, a chick nodal homologue, is expressed in the nascent prechordal mesoderm and we provide evidence that Nodal signalling can cooperate with Shh to induce the epiblast precursors to a floor-plate fate. These results indicate that a shared lineage with axial mesoderm cells is not a pre-requisite for floor plate differentiation and suggest parallels between the development of the floor plate in amniote and anamniote embryos.

Animals↗
PubMed2001

Embryonic stem cell-derived neurogenesis. Retinoic acid induction and lineage selection of neuronal cells.

Embryonic stem (ES) cells are able to differentiate in vitro into endodermal, mesodermal, and ectodermal cell types. However. the spontaneous development of neuronal cells from ES cells is rather limited. Therefore, specific protocols to increase the differentiation of neuronal cells have been established, such as retinoic acid (RA) induction and lineage selection of neuronal cells. High concentrations of RA resulted in efficient neuronal differentiation paralleled by the expression of tissue-specific genes, proteins, ion channels, and receptors in a developmentally controlled manner. Because the developmental pattern and survival capacity of RA-induced neuronal cells were limited, specific differentiation protocols by lineage selection of neuronal cells have been established using growth and extracellular matrix factors. After formation of cells of the three primary germ layers, mesodermal differentiation was inhibited by serum depletion, and neural precursor cells were generated by addition of basic fibroblast growth factor, followed by differentiation induction by neuronal differentiation factors. Further application of survival-promoting factors such as neurotrophic factors and cytokines at terminal stages resulted in a significant increase, survival, and maintenance of dopaminergic neurons. In the future, these cellular systems will be applicable: (1) for studying commitment and neuronal specification in vitro, (2) as pharmacological assays for drug screening, and (3) for the selective isolation of differentiated neuronal cells which may be used as a source for cell and tissue grafts.

Animals↗
PubMed1981

The gonads of human true hermaphrodites.

Gonadal distribution in 409 cases of human true hermaphroditism is reviewed. An ovary was found on the left side of the body in 62.8% of the cases and the testis on the right side in 59.5%. The ovotestis is the most common gonad of the true hermaphrodite; amongst 806 gonads in 406 cases it was found in 44.3%. In this paper we give a detailed description of the morphology of ovotestis, testis and ovary in the true hermaphrodite. In addition we discuss the effects of fetal androgens and Müllerian inhibiting factor on the Wolffian and Müllerian ducts. Correlations between chromosomal complement and gonadal distribution are presented. True hermaphrodites with a 46,XX karyotype most commonly have an ovary on one side and an ovotestis on the other side; those with a Y-chromosome have a testis in 61% of cases. An analysis of the ratio of ovarian and testicular tissue within ovotestes showed a continuum from very little ovarian tissue to a small portion of testicular tissue. Each type of tissue was clearly demarcated. Hypotheses for gonadal induction in the true hermaphrodite should take cognizance of these facts. True hermaphrodites with a 46,XX chromosomal complement were characterized by a male phenotype in 54% of cases. This group may suggest a greater testicular induction ability in the genome as compared to the 46% with a female phenotype.

Androgens↗
PubMed2001

Pattern formation during C. elegans vulval induction.

Studies of C. elegans vulval development provide insights into the process of pattern formation during animal development. The invariant pattern of vulval precursor cell fates is specified by the integration of at least two signaling systems. Recent findings suggest that multiple, partially redundant mechanisms are involved in patterning the vulval precursor cells. The inductive signal activates the LET-60/RAS signaling pathway and induces the 1 degree fate, whereas the lateral signal mediated by LIN-12/Notch is required for specification of the 2 degrees fate. Several regulatory pathways antagonize the RAS signaling pathway and specify the non-vulval 3 degrees fate in the absence of induction. The temporal and spatial regulation of VPC competence and production of the inductive and the lateral signal are precisely coordinated to ensure the wild-type vulval pattern.

Animals↗
PubMed1999

Migration of mesonephric cells into the mammalian gonad depends on Sry.

In mammals, the primary step in male sex determination is the initiation of testis development which depends on the expression of the Y-linked testis determining gene, Sry. The mechanisms by which Sry controls this process are unknown. Studies showed that cell migration from the adjacent mesonephros only occurs into XY gonads; however, it was not known whether this effect depended on Sry, another Y-linked gene, or the presence of one versus two X chromosomes. Here we provide genetic proof that Sry is the only Y-linked gene necessary for cell migration into the gonad. Cell migration from the mesonephros into the differentiating gonad is consistently associated with Sty's presence and with testis cord formation, suggesting that cell migration plays a critical role in the initiation of testis cord development. The induction of cell migration represents the earliest signaling pathway yet assigned to Sry.

Animals↗