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PubMed1990

Morphologic and biochemical alterations in rat prostatic tumors induced by fetal urogenital sinus mesenchyme.

Because fetal urogenital sinus mesenchyme (UGM) has been found to be highly inductive when recombined with normal adult prostate tissues or normal and neoplastic bladder epithelium, we investigated whether fetal UGM also interacts with established hormone-responsive and unresponsive rat Dunning and Nb prostate tumors. Our results indicate that: 1) fetal UGM acts directly on selected rat prostatic tumors by inducing histomorphologic changes (e.g., inducing acinar ductal structures and secretory activity) in the tumors toward more differentiated forms resembling that of the adult prostate gland; 2) fetal UGM either increased the growth rate of or maintained the sizes of three of the four interacting rat prostatic tumors; and 3) fetal UGM markedly reduced the lactate dehydrogenase activity of Nb-autonomous tumor toward a level comparable to that of the normal rat prostate gland. Our data suggest that fetal UGM can directly affect the growth and differentiative functions of selected rat prostatic tumors.

Animals↗
PubMed1987

Synergistic induction of mesoderm by FGF and TGF-beta and the identification of an mRNA coding for FGF in the early Xenopus embryo.

The primary patterning event in early vertebrate development is the formation of the mesoderm and its subsequent induction of the neural tube. Classic experiments suggest that the vegetal region signals the animal hemisphere to diverge from the pathway of forming ectoderm to form mesoderm such as muscle. Here we show that bovine basic FGF has a limited capacity to induce muscle actin expression in animal hemisphere cells. This level of expression can be raised to levels normally induced in the embryo by another mammalian growth factor, TGF-beta, which by itself will not induce actin expression. We show that the Xenopus embryo contains an mRNA encoding a protein highly homologous to basic FGF. These results together with the identification of a maternal mRNA with strong homology to TGF-beta, suggest that molecules closely related to FGF and TGF-beta are the natural inducers of mesoderm in vertebrate development.

Actins↗
PubMed1999

Developmental genetics of the Drosophila gut: specification of primordia, subdivision and overt-differentiation.

The Drosophila gut is composed of three major parts, the foregut, midgut and hindgut, which arise from anterior and posterior invaginations of the early blastoderm. We review the process of the specification of the gut primordia, subsequent subdivision and region-specific cell differentiation in terms of developmental genetics. Graded activities of maternal signals at anterior and posterior terminal domains of the blastoderm, being mediated by activities of two zygotic gap genes, tailless and huckebein, lead to the activation of key genes that determine the gut primordia: serpent (GATA factor gene) for the endodermal midgut; brachyenteron (Brachyury homolog) for the ectodermal hindgut. fork head (HNF-3 homolog) and caudal (Cdx homolog) are also essential for the development of all gut primordia or hindgut primordium, respectively. Subdivision of the midgut epithelium is regulated by inductive signals emanating from the visceral mesoderm, which is under the control of HOM-C genes. In contrast, pattern formation of the ectodermal foregut and hindgut is regulated by secreted signaling molecules, such as Wingless (Wnt homolog), Hedgehog and Decapentaplegic (Bmp-4 homolog), as in the case of segmented structures and imaginal discs. Finally, the gut is subdivided into at least 36 compartments that are recognized asminimum tissue units of regional differentiation. A few genes that are responsible for determining and maintaining the state of overt-differentiation of the compartments have also been reported. A marked feature of the genetic mechanism of the gut development is the unexpectedly wide spectrum of the similarities of relevant genes and regulatory pathways of gene expression between Drosophila and vertebrates, which may imply a prototypic style of body plan common to protostomes and deuterostomes.

Animals↗
PubMed2004

Hedgehog signaling is required for commitment but not initial induction of slow muscle precursors.

In zebrafish, skeletal muscle precursors can adopt at least three distinct fates: fast, non-pioneer slow, or pioneer slow muscle fibers. Slow muscle fibers develop from adaxial cells and depend on Hedgehog signaling. We analyzed when precursors become committed to their fates and the step(s) along their differentiation pathway affected by Hedgehog. Unexpectedly, we find that embryos deficient in Hedgehog signaling still contain postmitotic adaxial cells that differentiate into fast muscle fibers instead of slow. We show that by the onset of gastrulation, slow and fast muscle precursors are already spatially segregated but uncommitted to their fates until much later, in the segmental plate when slow precursors become independent of Hedgehog. In contrast, pioneer and non-pioneer slow muscle precursors share a common lineage from the onset of gastrulation. Our results demonstrate that slow muscle precursors form independently of Hedgehog signaling and further provide direct evidence for a multipotent muscle precursor population whose commitment to the slow fate depends on Hedgehog at a late stage of development when postmitotic adaxial cells differentiate into slow muscle fibers.

Animals↗
PubMed2001

The BMP/CHORDIN antagonism controls sensory pigment cell specification and differentiation in the ascidian embryo.

We have investigated the role of the bone morphogenetic protein (BMP) pathway during neural tissue formation in the ascidian embryo. The orthologue of the BMP antagonist, chordin, was isolated from the ascidian Halocynthia roretzi. While both the expression pattern and the phenotype observed by overexpressing chordin or BMPb (the dpp-subclass BMP) do not suggest a role for these factors in neural induction, BMP/CHORDIN antagonism was found to affect neural patterning. Overexpression of BMPb induced ectopic sensory pigment cells in the brain lineages that do not normally form pigment cells and suppressed pressure organ formation within the brain. Reciprocally, overexpressing chordin suppressed pigment cell formation and induced ectopic pressure organ. We show that pigment cell formation occurs in three steps. (1) During cleavage stages ectodermal cells are neuralized by a vegetal signal that can be substituted by bFGF. (2) At the early gastrula stage, BMPb secreted from the lateral nerve cord blastomeres induces those neuralized blastomeres in close proximity to adopt a pigment cell fate. (3) At the tailbud stage, among these pigment cell precursors, BMPb induces the differentiation of specifically the anterior type of pigment cell, the otolith; while posteriorly, CHORDIN suppresses BMP activity and allows ocellus differentiation.

Animals↗
PubMed2003

Induction of string rescues the neuroblast proliferation defect in trol mutant animals.

In trol mutants, neuroblasts fail to exit G1 for S phase. Increasing string expression in trol mutants rescues the number of S phase neuroblasts without an increase in M phase neuroblasts. Decreasing string expression further decreased the number of S phase neuroblasts. Coexpression of cyclin E and string did not produce additional S phase cells. Unlike cyclin E, cdk2, and cdk2AF, elevated expression of neither cyclin A, cyclin D, nor cdk1AF was able to promote S phase progression in arrested neuroblasts, indicating that String-induced activity of a Cyclin A or Cyclin D complex is unlikely to drive trol neuroblasts into S phase. Biochemical analyses revealed a rapid increase of Cyclin E-Cdk2 kinase activity to wild-type levels upon increased string expression. These results suggest that Drosophila Cdc25 may directly or indirectly increase the kinase activity of Cyclin E-Cdk2 complexes in vivo, thus driving arrested neuroblasts into cell division.

Alleles↗
PubMed1996

Digit induction by Hensen's node and notochord involves the expression of shh but not RAR-beta 2.

It is well established that Hensen's nodes can induce the formation of supernumerary digits after grafting into the anterior margin of the developing limb bud. The recent finding that distinct mesodermal cell populations are segregated within the node has made it possible to isolate different prospective cell types in an attempt to correlate digit-inducing ability with cell fate. We find that the prospective notochord cells contained within Hensen's node are able to induce supernumerary digits, whereas presumptive somite cells cannot. This early difference in inducing ability persists into later stages of development: epithelial somites are unable to induce while notochord from all lengths of the neuraxis continues to induce. Using probes to retinoic acid receptor-beta 2 and sonic hedgehog (shh) we find no evidence to support the idea that inducing tissues generate extra digits by releasing retinoic acid into adjacent limb tissue but find that the inducing ability of a tissue correlates with its expression of shh.

Animals↗
PubMed1995

Regulation of neural induction by the Chd and Bmp-4 antagonistic patterning signals in Xenopus.

In Drosophila the amount of neurogenic ectoderm, from which the central nervous system (CNS) derives, is regulated by a dorsal-ventral system of positional information in which two secreted molecules of antagonistic functions, decapentaplegic (dpp) and short-gastrulation (sog), play fundamental roles. The vertebrate homologue of dpp is either bmp-4 or bmp-2 (ref. 5), and the homologue os sog is chd (s-chordin). In Xenopus the CNS is induced by signals emanating from the organizer, and two proteins secreted by the organizer, noggin and follistatin, have been shown to induce neural tissue in animal-cap assays. Here we report that Chd, another organizer-specific secreted factor, has neuralizing activity and that this activity can be antagonized by Bmp-4. Inhibition of the function of the endogenous Bmp-4 present in the animal cap also leads to neural differentiation. We suggest that conserved molecular mechanisms involving chd/sog and bmp-4/dpp gene products pattern the ectoderm in Xenopus and in Drosophila.

Animals↗
PubMed1981

Ionic induction of the frog cement-gland cell from presumptive ectodermal tissues.

Cells of the superficial layer which had been explanted from the presumptive ectoderm of Rana japonica early gastrulae at stage 10 differentiated into cement-gland cells (CGCs) when cultured in Barth's solution containing 90-130 mM-NaCl, and into common epidermal cells and cilia cells when cultured in a solution containing 20-40 mM-NaCl. They failed to differentiate, however, when cultured in a solution in which NaCl is 15 mM or lower. The optimum condition for inducing the differentiation of CGC was stimulating them with a solution containing 130 mM-NaCl for 6-10 h at 18 degrees C, followed by culturing in a solution containing 15-40 mM-NaCl for 7 days. The greatest ability to react to the CGC-inducing stimuli resided in the superficial layer of the presumptive ectoderm of the embryo at stages 10-11. Under the optimum condition, the total volume of CGCs induced amounted to about 85% of the explanted tissue. High percentage comparable to this was obtained with stimulation by KCl, RbCl, sucrose or mannitol.

Animals↗
PubMed1996

Induction of a specific muscle cell type by a hedgehog-like protein in zebrafish.

The notochord plays a central role in vertebrate development, acting as a signalling source that patterns the neural tube and somites. In in vitro assays, the secreted protein Sonic hedgehog mimics the inducing effects of notochord on both presomitic mesoderm and neural plate explants of amniote embryos, suggesting that both patterning activities of the notochord may be mediated by this protein in vivo. In zebrafish, however, mutants with disrupted notochord development lack a specific muscle cell type, the muscle pioneers, although they retain the ability to induce neural differentiation, raising the possibility that neural tube and somite patterning may be mediated by distinct signals. Here we describe a new member of the hedgehog family, echidna hedgehog, that is expressed exclusively in the notochord and has the ability to rescue the differentiation of muscle pioneer cells in mutants with no notochord. Moreover, we show that a combination of ectopic echidna hedgehog and sonic hedgehog expression induces supernumary muscle pioneers in wild-type embryos, suggesting that both signals act sequentially to pattern the developing somites.

Amino Acid Sequence↗
PubMed2000

Genetic ablation reveals that the roof plate is essential for dorsal interneuron specification.

During neural development in vertebrates, a spatially ordered array of neurons is generated in response to inductive signals derived from localized organizing centres. One organizing centre that has been proposed to have a role in the control of neural patterning is the roof plate. To define the contribution of signals derived from the roof plate to the specification of neuronal cell types in the dorsal neural tube, we devised a genetic strategy to ablate the roof plate selectively in mouse embryos. Embryos without a roof plate lack all the interneuron subtypes that are normally generated in the dorsal third of the neural tube. Using a genetically based lineage analysis and in vitro assays, we show that the loss of these neurons results from the elimination of non-autonomous signals provided by the roof plate. These results reveal that the roof plate is essential for specifying multiple classes of neurons in the mammalian central nervous system.

Animals↗
PubMed1991

Dose and time-dependent mesoderm induction and outgrowth formation by activin A in Xenopus laevis.

We examined the quality of mesoderm induced by the action of activin A on the Xenopus presumptive ectoderm when various concentrations and treatment times were employed. The minimum concentration of activin A to induce mesodermal tissues was inversely proportional to its treatment time. The explants differentiated into different types of mesodermal tissues, from ventral-type to dorsal-type depending on the concentration of activin A and its treatment time. To confirm whether activin A has a role in establishing axial organization, activin A was injected into the blastocoel of late blastulae. About 70% of the injected embryos formed secondary tail-shaped outgrowths in which muscle and neural tube differentiated. The amount of activin A to form secondary outgrowths was 0.5-2.5 pg, roughly consistent with the amount estimated from in vitro experiments. As we have detected almost the same amount of activin homologue in the early embryos (Asashima et al., 1991a), we speculate that activin A may be the natural mesodermal inducer, and that it is responsible for establishing axial organization in the Xenopus embryo.

Activins↗
PubMed2000

Expression of activated MAP kinase in Xenopus laevis embryos: evaluating the roles of FGF and other signaling pathways in early induction and patterning.

FGF signaling has been implicated in germ layer formation and axial determination. An antibody specific for the activated form of mitogen-activated protein kinase (MAPK) was used to monitor FGF signaling in vivo during early Xenopus development. Activation of MAPK in young embryos is abolished by injection of a dominant negative FGF receptor (XFD) RNA, suggesting that MAPK is activated primarily by FGF in this context. A transition from cytoplasmic to nuclear localization of activated MAPK occurs in morula/blastula stage embryo animal and marginal zones coinciding with the proposed onset of mesodermal competence. Activated MAPK delineates the region of the dorsal marginal zone before blastopore formation and persists in this region during gastrulation, indicating an early role for FGF signaling in dorsal mesoderm. Activated MAPK was also found in posterior neural tissue from late gastrulation onward. Inhibition of FGF signaling does not block posterior neural gene expression (HoxB9) or activation of MAPK; however, inhibition of FGF signaling does cause a statistically significant decrease in the level of activated MAPK. These results point toward the involvement of other receptor tyrosine kinase signaling pathways in posterior neural patterning.

Active Transport, Cell Nucleus↗
PubMed1997

Ligand-bound RXR can mediate retinoid signal transduction during embryogenesis.

Retinoids regulate various aspects of vertebrate development through the action of two types of receptors, the retinoic acid receptors (RARs) and the retinoid-X-receptors (RXRs). Although RXRs bind 9-cis-retinoic acid (9cRA) with high affinity, in vitro experiments suggest that RXRs are for the most part not liganded, but serve as auxiliary factors forming heterodimers with liganded partner receptors such as RAR. Here we have used RXR- and RAR-specific ligands 4-[1-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydro-2-napthyl)ethenyl]b enzoic acid (LG69) and (E)-4-[2-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-2-naphthalenyl)-1-prope nyl]benzoic acid (TTNPB), and show that, in the context of an embryo, liganded RXR can mediate retinoid signal transduction. This conclusion emerges from examining the induction of several retinoid-responsive genes in the limb bud (Hoxb-6/-8, RARbeta) and in the developing central nervous system (Hoxb-1, otx-2). RARbeta and Hoxb-1 genes were most effectively activated by a combination of TTNPB and LG69, suggesting that the activation of these genes benefits from the presence of ligand-bound RAR and ligand-bound RXR. Hoxb-6/-8 genes were most efficiently induced by LG69, suggesting that liganded RXR can activate these genes. The regulation of the expression of the otx-2 gene was complex; expression was repressed by TTNPB, but such repression was relieved when LG69 was provided together with TTNPB, suggesting that ligand-bound RXR can overcome repression of transcription exerted by liganded RAR. Based on these findings, we propose that in our experimental system in which ligands are provided exogenously, transcriptional regulation of several genes involves liganded RXR.

Animals↗
PubMed1987

A mesoderm-inducing factor is produced by Xenopus cell line.

Inductive interactions play a major role in the diversification of cell types during vertebrate development. These interactions have been extensively studied in amphibian embryos (usually Xenopus laevis) where the earliest is mesoderm induction, in which an equatorial mesodermal rudiment is induced from the animal hemisphere under the influence of signal from the vegetal hemisphere. The molecular basis of mesoderm induction is unknown, although Tiedemann has isolated a protein form 9- to 13-day chick embryos that has the properties one would expect of a mesoderm-inducing factor. However, the relevance of this molecule to the events of early amphibian development is unclear, and it is a matter of some importance to discover a Xenopus mesoderm-inducing factor. In this paper I show that the Xenopus XTC cell line secretes mesoderm-inducing activity into the culture medium. Isolated animal pole regions cultured in XTC-conditioned medium differentiate into muscle and notochord, while controls form 'atypical epidermis'. Three different cell lines -XL, XL177 and KR- secrete no such activity indicates that the active principle is heat stable, trypsin sensitive, nondialysable, and has an apparent relative molecular mass of about 16,000. Work is in progress to characterize the activity further and to discover whether the mesoderm-inducing factor is also present in normal embryos.

Activins↗
PubMed1997

Cortical rotation is required for the correct spatial expression of nr3, sia and gsc in Xenopus embryos.

Beta-catenin, a component of the wnt-signal-transduction pathway, is essential for the formation of the dorsal axis in Xenopus laevis embryos. On the dorsal side of the embryo, beta-catenin is translocated into the nuclei via a process linked to cortical rotation. When cortical rotation is blocked by UV-irradiation, nuclear beta-catenin is found in the vegetal pole of the embryo. Here we show that overexpression of beta-catenin in animal cap explants, in the absence of mesoderm induction, is sufficient to activate the expression of genes with dorsalizing activity such as siamois (sia) and nodal-related 3 (nr3) but not goosecoid (gsc). In embryos ventralized by UV-treatment, the expression of the dorsal-specific genes sia, nr3 and gsc is induced at the vegetal pole after the Mid-Blastula-Transition (MBT). While nr3 and sia expression continues in these embryos until gastrula stages, gsc transcription cannot be maintained. We propose that the spatial separation of the expression domains of genes with dorsalizing activities and the prospective mesodermal region results in the loss of dorsal structures in the embryo. The role of cortical rotation is to generate an overlap of the region with dorsal axis-forming activity, indicated by nuclear translocation of beta-catenin, and the prospective mesoderm in the marginal zone to assure the correct positioning of the Spemann organizer.

Animals↗
PubMed1994

Ingrowth by photoreceptor axons induces transcription of a retrotransposon in the developing Drosophila brain.

The development of the lamina, the first optic ganglion of the fly visual system, depends on inductive cues from the innervating photoreceptor axons. lacZ expression from a P-element insertion, A72, occurs in the anlage of the lamina coincident with axon ingrowth from the eye imaginal disc. In eyeless mutants lacking photoreceptor axons, lacZ expression did not occur. The P-element was found to have inserted within the 3' long terminal repeat (LTR) of a '17.6' type retrotransposon. The expression pattern of 17.6 transcripts in the brain in wild-type and eyeless mutants paralleled the expression of the lacZ reporter. Analysis of 17.6 cis-regulatory sequences indicates that the lamina-specific expression is due to the combined action of an enhancer element in the LTR and a repressor element within the internal body of the retrotransposon. The regulation of the 17.6 retrotransposon provides a model for the study of innervation-dependent gene expression in postsynaptic cells during neurogenesis.

Animals↗
PubMedDate not supplied

How different types of pattern formation mechanisms affect the evolution of form and development.

Here we investigate how development and evolution can affect each other by exploring what kind of phenotypic variation is produced by different types of developmental mechanisms. A limited number of developmental mechanisms are capable of pattern formation in development. Two main types have been identified. In morphodynamic mechanisms, induction events and morphogenetic processes, such as simple growth, act at the same time. In morphostatic mechanisms, induction events happen before morphogenetic mechanisms, and thus growth cannot influence the induction of a pattern. We present a study of the variational properties of these developmental mechanisms that can help to understand how and why a developmental mechanism may become involved in the evolution and development of a particular morphological structure. Using existing models of pattern formation in teeth, an extensive simulation analysis of the phenotypic variation produced by different types of developmental mechanisms is performed. The studied properties include the amount and diversity of the phenotypic variation produced, the complexity of the phenotypic variation produced, and the relationship between phenotype and genotype. These variational properties are so different between different types of mechanisms that the relative involvement of these types of mechanisms in evolutionary innovation and in different stages of development can be estimated. In addition, type of mechanism affects the tempo and mode of morphological evolution. These results suggest that the basic principles by which development is organized can influence the likelihood of morphological evolution.

Animals↗