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PubMed1972

Preferential inhibition by proflavine of the hormonal induction of glutamine synthetase in embryonic neural retina.

The hormonal induction of glutamine synthetase (EC 6.3.1.2) in embryonic neural retina tissue in vitro is blocked preferentially and reversibly by proflavine (3,6-diaminoacridine) in the absence of cell or DNA replication; cell viability is not affected, and the synthesis of total cellular proteins and RNA is only slightly reduced. In the induction of this enzyme, there is a rapid increase in the synthesis and accumulation of the enzyme selectively elicited by the steroid inducer; for this effect, transcription is essential. Radioimmunochemical measurements have shown that proflavine inhibits induction by prevention of de novo synthesis of catalytically active and immunologically reactive glutamine synthetase protein. It does not measurably affect the uptake of the steroid inducer by the retina cells. Since the translation of this enzyme by preformed RNA templates is not stopped by proflavine, the inhibitory effect of proflavine on induction is apparently due to interference with transcriptional or pretranslational processes required for the provision of active transcripts for enzyme synthesis. The finding that proflavine inhibits preferentially a tissue-specific, inducible differentiation in postmitotic embryonic neural cells offers new approaches to the study of regulation of gene expression in eukaryotes.

Acridines↗
PubMed1975

Relationship of steroid structure to induction of chymotrypsinogen in embryonic chick pancreas in vitro.

The effect of steroid structure on induction of chymotrypsinogen in embryonic chick pancreas was examined in vitro. In order of decreasing potency cortisol, corticosterone, and 21-deoxycortisol are classified as optimal inducers, whereas 11beta-hydroxyprogesterone, 11-deoxycortisol, cortisone, 11-deoxycorticosterone and 17-alpha-hydroxyprogesterone are classified as suboptimal inducers. Progesterone was inactive. It is concluded that the relative importance of the steroid hydroxyl groups for activity is 11beta greater than 21 greater than 17 alpha, and that their effect is cumulative.

Adrenal Cortex Hormones↗
PubMed1983

Antiserum to rat visceral yolk sac endoderm induced abnormal embryonic development.

The induction of abnormal embryonic development by heterologous tissue antisera has been well established. The underlying mechanism whereby such teratogenesis occurs is not known. There were implications that visceral yolk sac endoderm might be involved. Endoderm was isolated from rat visceral yolk sac of 14th day of gestation using a nonenzymic procedure. The purity of the endoderm preparation was examined by electron microscopy. The preparation contained sheets of single layer of endodermal cells with no apparent contamination by the underlying mesenchyme or basal lamina. The specificity of the antiserum was examined by in vitro immunofluorescent localization studies. The antibodies against the endoderm localized only in the endodermal cells and some of the renal tubular cells. Intraperitoneal injection of the endoderm antiserum into 9-day pregnant rats resulted in congenital malformation, embryonic death, and fetal growth retardation. The effects of the antiserum were dose-dependent. The most frequently observed defects were anophthalmia and microphthalmia. Retarding effect of the antiserum on the growth of the embryo at the egg cylinder stage was also observed. In vivo immunofluorescent localization studies indicated that the endoderm antibodies localized only in the endodermal cells of the visceral yolk sac placenta; no localization was observed in the visceral yolk sac mesenchyme, basal lamina. Reichert's membrane, maternal kidney tissue or the embryo proper.

Animals↗
PubMed2002

Early subdivisions in the neural plate define distinct competence for inductive signals.

Regionalization of the embryonic brain is achieved through multi-step processes that operate sequentially and/or simultaneously. Localized sources of various signaling molecules act as organizing centers that pattern neighboring fields to create molecularly distinct domains. We investigated the mechanisms underlying the regionally distinct competence for two such organizing signals, Fibroblast growth factor 8 (Fgf8) and Sonic hedgehog (Shh), using chick embryos. First, we demonstrated that FGF receptor 1 (Fgfr1) and Fgfr3, expressed differentially in the developing brain, possess an equivalent potential to induce the regionally distinct Fgf8-responsive genes, depending on the anterior-posterior dimension of the brain. Next we found that homeodomain transcription factors Six3 and Irx3 can alter the regional responses to both Fgf8 and Shh in the forebrain. Six3 confers the ability to express Bf1, a gene essential for the telencephalon and eye development, and Nkx2.1, which is required for development of the hypothalamus. In contrast, Irx3 confers the ability to express En2 and Nkx6.1 in response to Fgf8 and Shh, respectively. Furthermore, an alteration in the region-specific response to Fgf8 upon misexpression of Irx3 resulted in transformation of diencephalic and possibly telencephalic tissues into the optic tectum. Finally, we demonstrated that Six3 and Irx3 can mutually repress their expression, which may contribute to the establishment of their complementary expression domains in the neural plate. These repressive interactions are specific, as Six3 did not repress Gbx2, and Irx3 did not disturb Otx2 expression. These findings provide evidence that the early embryonic forebrain is demarcated into two domains with distinct genetic programs, which argues against the authentic telendiencephalic subdivision.

Animals↗
PubMed1980

Effect of carcinogenic polycyclic aromatic hydrocarbons on mouse embryonic cells in culture: induction of spindle-shaped cells.

In cultured mouse embryonic cells (MECs) treated with benzo[a]pyrene (B[a]P), there appeared unusual type of fibroblasts, spindle-shaped cells (SP cells), which were characterized by their narrow bipolar shape, long cellular processes and optically distinct cell borders. Appearance of SP cells was massive and irreversible. The amount of SP cells increased with increasing concentrations of B[a]P, while early cytotoxicity did not. In various polycyclic aromatic hydrocarbons (PAHs) tested, only potent carcinogens (7,12-dimethylbenz[a]anthracene (DMBA), 3-methylcholanthrene (MCA), B[a]P, and dibenz[a,e]pyrene (DB[a,e]P) induced SP cells. Among them, PAH having higher Iball's index induced SP cells at lower concentration and at an earlier time. Weak or non-carcinogenic PAHs including 3-hydroxybenzo[a]-pyrene (3-OH-B[a]P) did not induce SP cells. alpha-Napthoflavon (alpha NF) suppressed the induction of SP cell by carcinogenic PAH. SP cells did not appear spontaneously under various abnormal culture conditions. These results indicate that carcinogenic PAHs induce the appearance of a specific type of fibroblast, SP cells in MEC cultures in accordance with their carcinogenicity.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1989

Initial GABAergic expression in embryonic amphibian neuroblasts after neural induction.

At the late gastrula-early neurula stage some embryonic neuroblasts from neural plate and neural fold present apparently as a consequence of neural induction, the capability to develop in vitro into different neuronal subpopulations (cholinergic, dopaminergic, noradrenergic, somatostatinergic and some other peptidergic subpopulations without ongoing influences from the chordamesoderm (Duprat et al., 1987). Using the same in vitro model system, the aim of the present work was to delineate the abilities of these neuroblasts to develop GABAergic traits. The initial appearance and development of GABAergic phenotype has been quantitated by assaying the activity of glutamic acid decarboxylase (GAD). GAD activity was undetectable at the early gastrula stage (stage 8a) and was slightly measurable at the early neurula stage (stage 14- onset of the culture). It increased subsequently over the next 14 days in vitro. The temporal pattern of appearance and development of GAD activity in culture was in agreement with that observed in vivo. Immunocytochemical studies showed that GABA-like immunoreactivity was expressed in vitro in a subpopulation of neurons. Thus the developmental program for GAD expression and GABA phenotype maturation is acquired at least in some neuronal precursors. These data together with previously reported results on the expression of cholinergic, catecholaminergic and peptidergic phenotypes demonstrate that different neuronal subpopulations emerge near the end of gastrulation i.e. immediately after neural induction. The embryonic origin of this neuroblast heterogeneity remains to be determined.

Animals↗
PubMed1970

Induction of glutamine synthetase in embryonic retina: its dependence on cell interactions.

A relation between enzyme induction in embryonic cells and cellular organization is indicated by the finding that the levels of glutamine synthetase induced by hydrocortisone in the embryonic neural retina in vitro are dependent on the associations between the retina cells. Intact retina tissue, aggregates of dissociated cells, and cells in monolayer culture showed a decreasing response, in this order, to glutamine synthetase induction. With time of culture, the enzyme activity continued to rise in the intact retina and in cell aggregates, but activity declined in monolayer cultures even though the inducer was continuously present. Dispersed cells cultured in monolayer without the inducer showed after 24 hours a loss of inducibility which could not be reversed by reaggregating such modified cells but could be prevented by maintaining the freshly dispersed cells at a low temperature.

Animals↗
PubMed1995

The matured eye of Xenopus laevis tadpoles produces factors that elicit a lens-forming response in embryonic ectoderm.

Previous studies have indicated that the outer cornea can undergo transdifferentiation to form a lens in the tadpole larva of Xenopus laevis following removal of the original lens. This transformation appears to require an interaction with the neural retina. In the present study, we carried out a series of experiments to determine if the matured tadpole eye can also elicit lens formation in embryonic ectoderm. Labeled embryonic ectoderm was removed from the presumptive lens-forming region, or from the belly region (ventral ectoderm), at various stages of development (stages 11-19, gastrula to neural tube stages) and implanted into the eye cavity (posterior chamber) of advanced stage 52-55 tadpoles. After 3 days, we examined the tadpoles and their implanted tissues for lens cell formation using lens-specific antibodies. Implanted presumptive lens ectoderm differentiated lens cells in a large number of cases. The percentage of cases forming lens cells and the extent of morphological differentiation increased with increasing age of the implanted tissue. Implanted ventral ectoderm also formed lens cells, although at a reduced frequency and with limited morphological differentiation. These results indicate that the environment of the matured tadpole eye cavity stimulates lens cell formation in both presumptive lens and nonlens ectoderm. The development of the implanted tissues was compared to that found in previous studies where these tissues were cultured as explants or transplanted to lens-forming regions during early development and subjected to various periods of embryonic lens induction. Together, these findings suggest that the process of embryonic lens formation is related to that involved in transdifferentiation of the tadpole cornea during "lens regeneration." However, the inductive effect of the matured tadpole eye is qualitatively different from that of the early period of embryonic lens induction and, while more intense, may be more closely related to that which takes place via the optic vesicle during the later phase of embryonic lens induction.

Animals↗
PubMed1989

Mesoderm induction and blood island formation by angiogenic growth factors and embryonic inducing factors.

Factors which induce mesoderm, including endothelium lined cavities and primitive blood cells in omnipotent amphibian ectoderm, have been isolated from different sources. Recently it was shown that angiogenic factors, which belong to the protein families of the heparin binding growth factors (acidic and basic fibroblast growth factor) and the transforming growth factors (TGF-beta 1 and -beta 2), also induce mesodermal tissues in amphibian ectoderm. In triturus ectoderm, capillary like endothelial networks are induced preferentially by the transforming growth factors. The relationship between growth factors and inducing factors is discussed.

Amphibians↗
PubMed1985

Chondrogenesis in agarose gel culture. A model for chondrogenic induction, proliferation and differentiation.

An in vitro model has been developed to study chondrogenic induction, proliferation and differentiation. Embryonic rat mesenchymal cells isolated from muscle and embedded in agarose were treated with a partially purified extract from bovine demineralized bone powder. Treated cells proliferated and synthesized matrix similar to differentiated chondrogenic cells in a dose-dependent manner. By employing an enzyme-linked immunosorbent assay (ELISA), cartilage-specific proteoglycan and type II collagen synthesis were quantitated. Of the cells tested, only embryonic mesenchymal cells from muscle responded to bone extract. Proteoglycan synthesis was sensitive to type of medium and cell density.

Animals↗
PubMed1992

Inhibition of differentiation by leukemia inhibitory factor distinguishes two induction pathways in P19 embryonal carcinoma cells.

The ability of leukemia inhibitory factor (LIF) to block differentiation of P19 embryonal carcinoma (EC) cells under a variety of induction conditions was determined. LIF inhibits differentiation under several conditions which lead to endodermal and mesodermal cell lineages including skeletal and cardiac muscle. In contrast, LIF does not block differentiation when cells are induced under conditions which lead to neuro-ectodermal cell types including neurons and astroglial cells. These studies demonstrate that P19 EC cell differentiation can be divided into LIF sensitive and insensitive pathways which correlate with differentiation of endodermal/mesodermal and neuro-ectodermal cell types, respectively. The effect of LIF on mRNA levels for several genes which have previously been implicated in mediating differentiation in P19 EC cells was determined. LIF has no effect on the mRNA levels for retinoic acid receptor (RAR) alpha, RAR beta, RAR gamma, jun A, jun D, c-fos, or fra-1. In contrast LIF stimulates jun B mRNA expression by a factor of four to six under all induction conditions.

Carcinoma↗
PubMed1995

Lymphohematopoietic development from embryonic stem cells in vitro.

Differentiation induction from embryonic stem (ES) cells to blood cells is one of the best systems to study the molecular mechanisms which are involved in the development and differentiation of lymphohematopoietic cells. Several systems including our new system (OP9 system) using a macrophage colony stimulating factor-deficient stromal cell line named OP9 are discussed in this paper. It is advantageous that the OP9 system does not require any exogenous growth factors or a complex embryoid structure for the induction. The OP9 system combined with genetic manipulation of ES cells should facilitate to elucidate molecular mechanisms during development and differentiation of blood cells including B-lineage cells.

Animals↗
PubMed1971

Changes in macromolecular synthesis associated with the induction of glutamine synthetase in embryonic retina.

The hydrocortisone-mediated induction of glutamine synthetase in the neural retina of chicken embryo in vitro is correlated with enhanced incorporation into protein of [(14)C]aspartic acid, an amino acid abundant in this enzyme. In the induced retina labeled with [(14)C]aspartic acid, a peak of radioactivity was detected in the region of the polysomal profile corresponding to polysomes comprising 12-14 ribosomes. In retinas labeled with [(3)H]uridine, an increased amount of radioactivity was also detected in the same polysomal region of the hydrocortisone-induced retina. If we assume a monocistronic messenger RNA for retinal glutamine synthetase, this region corresponds to the estimated size of the polysomes necessary for the translation of this enzyme. The evidence presented demonstrates a correlation between these changes in incorporation and the induction of glutamine synthetase.

Animals↗
PubMed1982

Induction of androgen receptor formation by epithelium-mesenchyme interaction in embryonic mouse mammary gland.

The role of tissue interaction in the development of hormone responsiveness was studied in the embryonic mammary gland of the mouse, which becomes sensitive to testosterone on day 14. Previously, the mesenchyme had been identified as the sole target tissue for the hormone, although it was also demonstrated that its response to testosterone required the presence of mammary epithelium. Using autoradiography, we now show that [3H]testosterone or [3H]5 alpha-dihydrotestosterone is bound only by those mesenchymal cells closest to the epithelial mammary bud. When mammary epithelia were experimentally associated with mesenchyme of the mammary region and cultured together for 3 days in vitro, they also became surrounded by several layers of [3H]testosterone-binding mesenchymal cells. Correspondingly, this tissue association was accompanied by a substantial increase of androgen-binding sites in the explants. No hormone-building mesenchymal cells were seen in combinations with epidermis or pancreas epithelium; only salivary epithelium showed a weak positive effect. From these results we conclude that mammary epithelium induces the formation of androgen receptors in adjacent mesenchyme and thereby controls the development of androgen responsiveness in this tissue.

Animals↗
PubMed2004

Specific beta1 integrins mediate adhesion, migration, and differentiation of neural progenitors derived from the embryonic striatum.

Early inductive signals within the embryonic mammalian forebrain establish two major germinal regions along the dorsal-ventral axis. The dorsal germinal zone eventually forms the cerebral cortex while the ventral ganglionic eminence primarily forms the striatum and globus pallidus. The mechanisms leading to patterning of specific forebrain structures from these distinct germinal regions are not fully understood but may involve the adhesive and migratory properties of regionally specified cells and their interactions with the extracellular environments in which they reside. In the present study, we isolated ganglionic eminence neural progenitor cells (geNPC), precursors of the adult striatum, from the ventral forebrain germinal zone and analyzed adhesion, migration, and differentiation of geNPC on various extracellular matrix (ECM) substrates in vitro. Specifically, we evaluated the role of beta1 integrins, a family of cell surface receptors important in neural development, in mediating geNPC behavior on ECM molecules expressed in embryonic brain tissue. Adhesion and migration of geNPC were significantly enhanced on laminin (LN) and fibronectin (FN) relative to other ECM substrates. Antibody perturbation experiments revealed that although geNPC express several beta1 integrins (alpha1beta1, alpha2beta1, alpha3beta1, alpha5beta1, alpha6beta1, alphavbeta1), adhesion and migration on LN and FN were primarily mediated by alpha6beta1 and alpha5beta1, respectively, and these interactions were confirmed by biochemical cross-link/extraction procedures. Finally, neuronal differentiation of geNPC was enhanced on LN, indicating a role for LN in geNPC differentiation. beta1 integrin-ECM interactions may contribute to basic mechanisms of striatal development and may explain the potent migratory capacity of geNPC transplanted into the adult brain.

Animals↗
PubMed1999

Induction of apoptosis by beta radiation from tritium compounds in mouse embryonic brain cells.

Induction of apoptosis by tritium exposure was investigated in both cultured embryonic mid brain cells and brain sections of embryos and of newborns in mice. In the cultures of mid brain cells, addition of methyl-3H-thymidine (3H-TdR) (21 kBq mL(-1)) and tritiated water (5.616 MBq mL(-1)) induced late appearances and low percentages of apoptosis when compared to x-irradiation at the ID50 dose, the inhibitory dose that reduced cellular differentiation by 50% of the control. A significant increase in p53 protein was detected about 2 h before the marked appearance of apoptosis. The pregnant mice were given an intraperitoneal injection of tritiated water at the concentration of 481.8 kBq g(-1) of body weight on gestation day 12.5, by which treatment behavioral changes in the offspring occurred. Increased apoptotic cells were observed in the neural tube of embryos from 1 d after the injection to 1 wk postnatal age. Apoptosis induced by x-rays appeared 2 h after irradiation, with a peak at 4 h. Increase of apoptotic cells was also found in the brain cortexes of newborns. The percentage of apoptosis in the brain was higher in the prenatal tritiated water exposed mice than in the prenatal x-irradiated mice. Possible mechanisms on apoptosis and its relation to the higher relative biological effectiveness value of tritium beta-rays are discussed.

Animals↗