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PubMed1994

Studies with a Xenopus BMP receptor suggest that ventral mesoderm-inducing signals override dorsal signals in vivo.

We report the isolation of a Xenopus BMP receptor that is expressed maternally in the appropriate location to play a role in mesoderm induction. This receptor binds both BMP-2 and BMP-4 with high affinity. A truncated form of this BMP receptor specifically blocks BMP-4 signaling. Expression of this truncated BMP receptor during embryogenesis converts ventral mesoderm to dorsal mesoderm. Contrary to the popularly held view that ventral is the ground state for all mesoderm, our results suggest that formation of ventral mesoderm requires an active signal and that, in the absence of this ventral signal, dorsal mesoderm is formed.

Activins↗
PubMed1997

The dorsalizing and neural inducing gene follistatin is an antagonist of BMP-4.

Specific signaling molecules play a pivotal role in the induction and specification of tissues during early vertebrate embryogenesis. BMP-4 specifies ventral mesoderm differentiation and inhibits neural induction in Xenopus, whereas three molecules secreted from the organizer, noggin, follistatin and chordin dorsalize mesoderm and promote neural induction. Here we report that follistatin antagonizes the activities of BMP-4 in frog embryos and mouse teratocarcinoma cells. In Xenopus embryos follistatin blocks the ventralizing effect of BMP-4. In mouse P19 cells follistatin promotes neural differentiation. BMP-4 antagonizes the action of follistatin and prevents neural differentiation. In addition we show that the follistatin and BMP-4 proteins can interact directly in vitro. These data provide evidence that follistatin might play a role in modulating BMP-4 activity in vivo.

Animals↗
PubMed1991

Injected Wnt RNA induces a complete body axis in Xenopus embryos.

Studies in Xenopus have shown that growth factors of the TGF beta and Wnt oncogene families can mimic aspects of dorsal axis formation. Here we directly compare the inductive properties of two Wnt proteins by injecting synthetic mRNA into developing embryos. The results show that Wnt-1 and Xwnt-8 can induce a new and complete dorsal axis and can rescue the development of axis-deficient, UV-irradiated embryos. In contrast, activin mRNA injection induces only a partial dorsal axis that lacks anterior structures. These studies demonstrate that the mechanism of Wnt-induced axis duplication results from the creation of an independent Spemann organizer. The relationship between the properties of the endogenous dorsal inducer and the effects of Wnts and activins is discussed.

Activins↗
PubMed1999

The lin-11 LIM domain transcription factor is necessary for morphogenesis of C. elegans uterine cells.

The Caenorhabditis elegans hermaphrodite egg-laying system comprises several tissues, including the uterus and vulva. lin-11 encodes a LIM domain transcription factor needed for certain vulval precursor cells to divide asymmetrically. Based on lin-11 expression studies and the lin-11 mutant phenotype, we find that lin-11 is also required for C. elegans uterine morphogenesis. Specifically, lin-11 is expressed in the ventral uterine intermediate precursor (pi) cells and their progeny (the utse and uv1 cells), which connect the uterus to the vulva. Like (pi) cell induction, the uterine lin-11 expression responds to the uterine anchor cell and the lin-12-encoded receptor. In wild type animals, the utse, which forms the planar process at the uterine-vulval interface, fuses with the anchor cell. We found that, in lin-11 mutants, utse differentiation was abnormal, the utse failed to fuse with the anchor cell and a functional uterine-vulval connection was not made. These findings indicate that lin-11 is essential for uterine-vulval morphogenesis.

Amino Acid Motifs↗
PubMed2000

Long-term evaluation of bone formation by osteogenic protein 1 in the baboon and relative efficacy of bone-derived bone morphogenetic proteins delivered by irradiated xenogeneic collagenous matrices.

To investigate the long-term efficacy of irradiated recombinant human osteogenic protein 1 (hOP-1) in bone regeneration and morphogenesis, hOP-1 was combined with a bovine collagenous matrix carrier (0, 0.1, 0.5, and 2.5 mg hOP-1/g of matrix), sterilized with 2.5 Mrads of y-irradiation, and implanted in 80 calvarial defects in 20 adult baboons (Papio ursinus). The relative efficacy of partially purified bone-derived baboon bone morphogenetic proteins (BMPs), known to contain several osteogenic proteins, was compared with the recombinant hOP-1 device in an additional four baboons. Histology and histomorphometry on serial undecalcified sections prepared from the specimens harvested on day 90 and day 365 showed that gamma-irradiated hOP-1 devices induced regeneration of the calvarial defects by day 90, although with reduced bone area compared with a previous published series of calvarial defects treated with nonirradiated hOP-1 devices. One year after application of the irradiated hOP-1 devices, bone and osteoid volumes and generated bone tissue areas were comparable with nonirradiated hOP-1 specimens. Moreover, 365 days after healing regenerates induced by 0.5 mg and 2.5 mg of irradiated hOP-1 devices showed greater amounts of bone and osteoid volumes when compared with those induced by nonirradiated hOP-1 devices. On day 90, defects treated with 0.1 mg and 0.5 mg of bone-derived baboon BMPs, combined with irradiated matrix, showed significantly less bone compared with defects receiving irradiated devices containing 0.1 mg and 0.5 mg hOP-1; 2.5 mg of partially purified BMPs induced bone and osteoid volumes comparable with the 0.1-mg and 0.5-mg hOP-1 devices. Control specimens of y-irradiated collagenous matrix without hOP-1 displayed a nearly 2-fold reduction in osteoconductive bone repair when compared with nonirradiated controls. These findings suggest that the reduction in bone volume and bone tissue area on day 90 may be caused by a reduced performance of the irradiated collagenous matrix substratum rather than to a reduction in the biological activity of the irradiated recombinant osteogenic protein. This is supported by the results of in vitro and in vivo studies performed to determine the structural integrity of the recovered gamma-irradiated hOP-1 before application in the baboon. Recoveries by high-performance liquid chromatography (HPLC) and sodium dodecyl sulfate/ polyacrylamide gel electrophoresis (SDS/PAGE)/immunoblot analyses indicated that doses of 2.5-3 Mrads of gamma-irradiation did not significantly affect the structural integrity of the recovered hOP-1. Biological activity of the recovered hOP-1 was confirmed in vitro by showing induction of alkaline phosphatase activity in rat osteosarcoma cells (ROS) and in vivo by de novo endochondral bone formation in the subcutaneous space of the rat. These findings in the adult primate indicate that a single application of gamma-irradiated hOP-1 combined with the irradiated xenogeneic bovine collagenous matrix carrier is effective in regenerating and maintaining the architecture of the induced bone at doses of 0.5 mg/g and 2.5 mg/g of carrier matrix.

Alkaline Phosphatase↗
PubMed1999

Hedgehog signal transduction: from flies to vertebrates.

The patterning and morphogenesis of multicellular organisms require a complex interplay of inductive signals which control proliferation, growth arrest, and differentiation of different cell types. A number of such signaling molecules have been identified in vertebrates and invertebrates. The molecular dissection of these pathways demonstrated that in vertebrates, mutations or abnormals function of these signaling pathways were often associated with developmental disorders and cancer formation. The Hedgehog (Hh) family of secreted proteins provides a perfect example of such signaling proteins. In the following review, we will not discuss in detail the role of Hh as a morphogen, but rather focus on its signal transduction pathway and its role in various human disorders.

Chromosome Aberrations↗
PubMed2002

Effects of heterodimerization and proteolytic processing on Derrière and Nodal activity: implications for mesoderm induction in Xenopus.

Derrière is a recently discovered member of the TGFbeta superfamily that can induce mesoderm in explant assays and is expressed at the right time and location to mediate mesoderm induction in response to VegT during Xenopus embryogenesis. We show that the ability of Derrière to induce dorsal or ventral mesoderm depends strictly on the location of expression and that a dominant-negative Derrière cleavage mutant completely blocks all mesoderm formation when ectopically expressed. This differs from the activity of similar Xnr2 cleavage mutant constructs, which are secreted and retain signaling activity. Additional analysis of mesoderm induction by Derrière and members of the Nodal family indicates that these molecules are involved in a mutual positive-feedback loop and antagonism of either one of the signals can reduce the other. Interaction between Derrière and members of the Nodal family is also shown to occur through the formation of heterodimeric ligands. Using an oocyte expression system we show direct interaction between the mature Derrière ligand and members of both the Nodal and BMP families. Taken together, these findings indicate that Derrière and Nodal proteins probably work cooperatively to induce mesoderm throughout the marginal zone during early Xenopus development.

Amino Acid Sequence↗
PubMed1997

Notochord induction of zebrafish slow muscle mediated by Sonic hedgehog.

The patterning of vertebrate somitic muscle is regulated by signals from neighboring tissues. We examined the generation of slow and fast muscle in zebrafish embryos and show that Sonic hedgehog (Shh) secreted from the notochord can induce slow muscle from medial cells of the somite. Slow muscle derives from medial adaxial myoblasts that differentiate early, whereas fast muscle arises later from a separate myoblast pool. Mutant fish lacking shh expression fail to form slow muscle but do form fast muscle. Ectopic expression of shh, either in wild-type or mutant embryos, leads to ectopic slow muscle at the expense of fast. We suggest that Shh acts to induce myoblasts committed to slow muscle differentiation from uncommitted presomitic mesoderm.

Animals↗
PubMed2005

Lens-forming competence in the epidermis of Xenopus laevis during development.

In larval X. laevis the capacity to regenerate a lens under the influence of inductive factors present in the vitreous chamber is restricted to the outer cornea and pericorneal epidermis (Lentogenic Area, LA). However, in early embryos, the whole ectoderm is capable of responding to inductive factors of the larval eye forming lens cells. In a previous paper, Cannata et al. (2003) demonstrated that the persistence of lens-forming competence in the LA is the result of early signals causing lens-forming bias in the presumptive LA and of late signals from the eye causing cornea development. This paper analyzes 1) the decrease of the lens-forming capacity in ectodermal regions both near LA (head epidermis) and far from LA (flank epidermis) during development, 2) the capacity of the head epidermis and flank epidermis to respond to lens-competence promoting factors released by an eye transplanted below these epidermal regions, and 3) the eye components responsible for the promoting effect of the transplanted eye. Results were obtained by implanting fragments of ectoderm or epidermis into the vitreous chamber of host tadpoles and by evaluating the percentage of implants positive to a monoclonal antibody anti-lens. These results demonstrated that the lens-forming competence in the flank region is lost at the embryonic stage 30/31 and is weakly restored by eye transplantation; however, lens-forming competence in the head region is lost at the larval stage 48 and is strongly restored by eye transplantation. The authors hypothesize that during development the head ectoderm outside the LA is attained by low levels of the same signals that attain the LA and that these signals are responsible for the maintenance of lens-forming competence in the cornea and pericorneal epidermis of the larva. In this hypothesis, low levels of these signals slacken the decrease of the lens-forming competence in the head ectoderm and make the head epidermis much more responsive than the flank epidermis to the effect of promoting factors released by a transplanted eye. Results obtained after transplantation of eyes deprived of some components indicate that the lens and the retina are the main source of these promoting factors. The immunohistochemical detection of the FGFR-2 (bek variant) protein in the epidermis of stage 53 larvae submitted to eye transplantation at stage 46 showed that the eye transplantation increased the level of FGFR-2 protein in the head epidermis but not in the flank epidermis, indicating that the lens-forming competence in X. laevis epidermis could be related to the presence of an activated FGF receptor system in the responding tissue.

Animals↗
PubMed1997

Dorsal-ventral patterning during neural induction in Xenopus: assessment of spinal cord regionalization with xHB9, a marker for the motor neuron region.

While the role of the notochord and floor plate in patterning the dorsal-ventral (D/V) axis of the neural tube is clearly established, relatively little is known about the earliest stages of D/V regionalization. In an effort to examine more closely the initial, preneural plate stages of regionalization along the prospective D/V neural axis, we have performed a series of explant experiments employing xHB9, a novel marker of the motor neuron region in Xenopus. Using tissue recombinants and Keller explants we show that direct mesodermal contact is both necessary and sufficient for the initial induction of xHB9 in the motor neuron region. We also show that presumptive neural plate explants removed as early as midgastrulation and cultured in isolation are already specified to express xHB9 but do so in an inappropriate spatial pattern while identical explants are specified to express the floor plate marker vhh-1 with correct spatial patterning. Our data suggest that, in addition to floor plate signaling, continued interactions with the underlying mesoderm through neural tube stages are essential for proper spatial patterning of the motor neuron region.

Amino Acid Sequence↗
PubMed1996

Essential role of stromal mesenchyme in kidney morphogenesis revealed by targeted disruption of Winged Helix transcription factor BF-2.

Metanephric mesenchyme gives rise to both the epithelial cells of the nephron and the stromal cells of the mature kidney. The function of the stroma. in kidney morphogenesis is poorly understood. We have generated mice with a null mutation in the Winged Helix (WH) transcription factor BF-2 to examine its function during development. BF-2 expression within the developing kidney is restricted to the stromal cell lineage. Homozygotes die within the first 24 hr after birth with abnormal kidneys. Mutant kidneys are small, fused longitudinally, and rotated 90 degrees ventrally. Histological examination reveals a smaller collecting system, numerous large condensations of mesenchyme, and a decrease in the number of nephrons. Using molecular markers we show that induction and condensation of the nephrogenic mesenchyme occurs normally in mutant. The disruption of BF-2 reduces the rate of differentiation of the condensed mesenchyme into tubular epithelium, as well as the rate of growth and branching of the ureter and collecting system. Our findings demonstrate that BF-2 and stromal cells have essential functions during kidney morphogenesis. Furthermore, they suggest that BF-2 controls the production, by the stroma, of signals or factors that are required for the normal transition of induced mesenchyme into tubular epithelium and full growth and branching of the collecting system.

Animals↗
PubMed1991

Injected Xwnt-8 RNA acts early in Xenopus embryos to promote formation of a vegetal dorsalizing center.

Expression cloning from a pool of gastrula cDNAs identified the Wnt family member Xwnt-8 as having dorsal axis-inducing activity in Xenopus embryos. Microinjected Xwnt-8 mRNA was able to rescue the development of a dorsally complete anterior-posterior axis in embryos ventralized by exposure to UV light. Axis induction was observed in embryos injected in either marginal or vegetal blastomeres at the 32-cell stage. Vegetal blastomeres receiving Xwnt-8 mRNA contributed progeny not to the induced dorsal axis, but to the endoderm, a result consistent with Xwnt-8 causing cells to act as a Nieuwkoop center (the vegetal-inducing component of normal dorsal axis formation), rather than as a Spemann organizer (the induced dorsal marginal zone component that directly forms the dorsal mesoderm). Xwnt-8, which is normally expressed ventrally in midgastrula and neurula embryos, appears to mimic, when injected, maternally encoded dorsal mesoderm-inducing factors that act early in development.

Animals↗
PubMed1991

The role of fibroblast growth factor in eye lens development.

In this review we have presented evidence that FGF plays an important role in inducing events in lens morphogenesis and growth. Our studies show that FGF stimulates lens epithelial cells in explants to proliferate, migrate, and differentiate into fibers at low, medium, and high concentrations, respectively. This has some important implications for understanding the behavior of lens cells in the eye. The fact that aFGF is detected in the equatorial region of the lens where cells are actively proliferating, possibly migrating, and differentiating into fibers suggests that these events may be under autocrine control in vivo, at least to some extent. Because FGF is also present in the ciliary and iridial region of retina and in the vitreous, paracrine control may also be involved. Cell proliferation, fiber differentiation, and (possibly) cell migration occur in characteristic spatial patterns that are related to distinct compartments of the lens. We suggest that cells in the germinative zone receive only a low level of FGF stimulation arising from the cells themselves and possibly also from the ciliary and iridial regions of the retina but, whatever the source, this is only sufficient to stimulate proliferation. Lens epithelial cells that migrate or are displaced into the transitional zone below the lens equator receive some FGF from these sources but in addition receive a strong stimulus from the high level of FGF in the vitreous; thus, fiber differentiation is induced. Cells at the junction between these two zones may receive an intermediate level of FGF stimulation, sufficient to induce cell migration. In essence, we are proposing that, in the eye, FGF acts as a lens morphogen in the sense that different levels of FGF stimulation elicit different lens cell responses. Hence its characteristic distribution in the eye establishes lens polarity and growth patterns. Since FGF has an inductive effect on lens cells from mature age animals, we also propose that this specific distribution of FGF in the eye is also important for maintenance of a normal lens throughout life. Finally the synergistic effects of insulin/IGF on the FGF-induced responses highlight the importance of considering the distribution of members of the insulin/IGF family of molecules in vivo. Mechanisms that control levels of both the FGF and insulin/IGF families of factors in the eye are probably of crucial importance in the formation and maintenance of a normal lens.

Aging↗
PubMed1994

Sex determination of the Drosophila germ line: tra and dsx control somatic inductive signals.

In Drosophila, the sex of germ cells is determined by cell-autonomous and inductive signals. XY germ cells autonomously enter spermatogenesis when developing in a female host. In contrast, XX germ cells non-autonomously become spermatogenic when developing in a male host. In first instar larvae with two X chromosomes, XX germ cells enter the female or the male pathway depending on the presence or absence of transformer (tra) activity in the surrounding soma. In somatic cells, the product of tra regulates the expression of the gene double sex (dsx) which can form a male-specific or a female-specific product. In dsx mutant larvae, XX and XY germ cells develop abnormally, with a seemingly intersexual phenotype. This indicates that female-specific somatic dsx products feminize XX germ cells, and male-specific somatic dsx products masculinize XX and XY germ cells. The results show that tra and dsx control early inductive signals that determine the sex of XX germ cells and that somatic signals also affect the development of XY germ cells. XX germ cells that develop in pseudomales lacking the sex-determining function of Sxl are spermatogenic. If, however, female-specific tra functions are expressed in these animals, XX germ cells become oogenic. Furthermore, transplanted XX germ cells can become oogenic and form eggs in XY animals that express the female-specific function of tra. Therefore, TRA product present in somatic cells of XY animals or in animals lacking the sex-determining function of Sxl, is sufficient to support developing XX germ cells through oogenesis.

Animals↗
PubMed1984

Differentiation of allantoic endoderm implanted into the presumptive digestive area in avian embryos. A study with organ-specific antigens.

Quail allantoic endoderm was implanted into the presumptive digestive-tract area of chick embryos, and the differentiation of the endoderm was examined morphologically and immunocytochemically with antisera against pepsinogens and sucrase. The allantoic endoderm was incorporated into the host digestive organs. It often became continuous with the host endoderm and formed a chimaeric digestive-tract epithelium. It differentiated morphologically into the epithelium of the digestive organ into which it was incorporated, showing the morphological inductive ability in situ of the digestive-tract mesenchyme against the allantoic endoderm. However, the allantoic endoderm did not produce pepsinogens even when it was incorporated into the host proventricular mesenchyme and formed well-developed proventricular glands. This result indicates that the heterotypic morphogenesis of the allantoic endoderm is not necessarily accompanied by the heterotypic cytodifferentiation. In contrast, the anti-sucrase antiserum-reactive cells often differentiated in the allantoic endoderm incorporated into not only the intestine but also other organs. This confirmed our previous observation that the allantoic endoderm has a tendency to differentiate into the intestinal epithelium in the heterologous environment.

Animals↗
PubMed1993

[Induction phenomena during vertebrate limb development and homeo box gene expression].

In tetrapod vertebrates, limbs are formed as a result of inductive interactions between ectoderm and mesoderm. The mesoderm from the limb field induces the formation, in the ectoderm, of a pseudo-stratified epithelium, the apical ectodermal ridge, which in turn is required for limb mesoderm outgrowth and patterning. Homeobox genes from the msh family are expressed in the apical region of limb bud mesoderm. Using the potential of chick experimental embryology, we have demonstrated that these genes respond to ecto-mesodermal induction at this site and may be implicated in the response of the mesoderm to the ectodermal inductive activity. This property appears to be more general for the sites in the embryo which grow and are patterned as a result of interactions between ectoderm and subjacent mesoderm, since many of them are places for the expression of the msh-related genes (e.g. fronto-nasal and maxillary processes, tooth germ, genital tubercle). These genes might be implicated in patterning events at these sites through the activation of other genes directly involved in the definition of positional information, such as Hox genes.

Amino Acid Sequence↗
PubMed1995

Regionalization of the forebrain from neural plate to neural tube.

The vertebrate central nervous system is subdivided into distinct regions along the anteroposterior axis. It has been suggested that segmentation may play an important role in the regionalization and patterning of the neural tube, in particular in the development of the hindbrain. Recent evidence suggests that this may be true also in the forebrain. Several criteria that have been used to define segments and that have led to different views on how the anterior neural tube is subdivided will be discussed. However, regionalization of the neural ectoderm is a gradual and continuous process that starts as early as the induction of neural ectoderm. At the neural plate stage, distinct domains of gene expression have been established, indicating that a certain amount of regionalization has already taken place. Segmentation, as defined by lineage restriction between proposed segments or by the formation of morphological segment boundaries, is not thought to have occurred at the neural plate. When viewed in this context, segmentation may be considered a relatively late event in the ontogenesis of the nervous system. The early pattern of gene expression, the organization of the neural plate, and the underlying signals and tissue interactions may provide us with a better understanding of how the forebrain is regionalized.

Animals↗
PubMed1996

Activation of two Cynops genes, fork head and sonic hedgehog, in animal cap explants.

We have isolated cDNAs of sonic hedgehog (shh) and fork head from Cynops (Japanese newt) embryo. Their expression was investigated in relation to mesoderm induction by activin and basic fibroblast growth factor (bFGF). Different from these homologs in Xenopus, they are activated not only by activin but also by bFGF in animal cap explants, showing a difference of animal pole cells in responsiveness to bFGF between Cynops and Xenopus. We also investigated the involvement of fork head in shh activation. The expression of shh was activated in animal caps which overexpressed either of two Xenopus fork head homologs, pintallavis/XFD-1 or XFKH-1/XFD-1', indicating that fork head up-regulates the transcription of shh in Cynops embryo.

Activins↗