Biomedical subjects

C Kintner

Publications and source records attributed to C Kintner.

At least 37 records · Page 2Linked to original sources

PubMed1998

Differential expression and function of cadherin-6 during renal epithelium development.

The cadherin gene family encodes calcium-dependent adhesion molecules that promote homophilic interactions among cells. During embryogenesis, differential expression of cadherins can drive morphogenesis by stimulating cell aggregation, defining boundaries between groups of cells and promoting cell migration. In this report, the expression patterns of cadherins were examined by immunocytochemistry and in situ hybridization in the embryonic kidney, during the time when mesenchymal cells are phenotypically converted to epithelium and the pattern of the developing nephrons is established. At the time of mesenchymal induction, cadherin-11 is expressed in the mesenchyme but not in the ureteric bud epithelium, which expresses E-cadherin. The newly formed epithelium of the renal vesicle expresses E-cadherin near the ureteric bud tips and cadherin-6 more distally, suggesting that this primitive epithelium is already patterned with respect to progenitor cell types. In the s-shaped body, the cadherin expression patterns reflect the developmental fate of each region. The proximal tubule progenitors express cadherin-6, the distal tubule cells express E-cadherin, whereas the glomeruli express P-cadherin. Ultimately, cadherin-6 is down-regulated whereas E-cadherin expression remains in most, if not all, of the tubular epithelium. Antibodies generated against the extracellular domain of cadherin-6 inhibit aggregation of induced mesenchyme and the formation of mesenchyme-derived epithelium but do not disrupt ureteric bud branching in vitro. These data suggest that cadherin-6 function is required for the early aggregation of induced mesenchymal cells and their subsequent conversion to epithelium.

Animals↗

PubMed1997

cash4, a novel achaete-scute homolog induced by Hensen's node during generation of the posterior nervous system.

In vertebrate embryos, the precursor cells of the central nervous system (CNS) are induced by signaling from the organizer region. Here we report the isolation of a novel vertebrate achaete-scute homolog, cash4, which is expressed in the presumptive posterior nervous system in response to such signaling. cash4 is first expressed in epiblast cells flanking the late-phase organizer (Hensen's node), which retains its ability to induce cash4 during regression to the caudal end of the embryo. We show that these node-derived signals can be mimicked in vivo by the activity of fibroblast growth factor (FGF). We demonstrate that cash4 can substitute for the achaete/scute genes in the fly and that it also has proneural activity in vertebrate embryos. Together these results suggest that cash4 functions as a proneural gene downstream of node-derived signals (including FGF) to promote the formation of the neural precursors that will give rise to the posterior CNS in the chick embryo.

Amino Acid Sequence↗

PubMed1997

Expression of Pax-3 is initiated in the early neural plate by posteriorizing signals produced by the organizer and by posterior non-axial mesoderm.

Pax-3 is a paired-type homeobox gene that is specifically expressed in the dorsal and posterior neural tube. We have investigated inductive interactions that initiate Pax-3 transcript expression in the early neural plate. We present several lines of evidence that support a model where Pax-3 expression is initiated by signals that posteriorize the neuraxis, and then secondarily restricted dorsally in response to dorsal-ventral patterning signals. First, in chick and Xenopus gastrulae the onset of Pax-3 expression occurs in regions fated to become posterior CNS. Second, Hensen's node and posterior non-axial mesoderm which underlies the neural plate induce Pax-3 expression when combined with presumptive anterior neural plate explants. In contrast, presumptive anterior neural plate explants are not competent to express Pax-3 in response to dorsalizing signals from epidermal-ectoderm. Third, in a heterospecies explant recombinant assay with Xenopus animal caps (ectoderm) as a responding tissue, late, but not early, Hensen's node induces Pax-3 expression. Chick posterior non-axial mesoderm also induces Pax-3, provided that the animal caps are neuralized by treatment with noggin. Finally we show that the putative posteriorizing factors, retinoic acid and bFGF, induce Pax-3 in neuralized animal caps. However, blocking experiments with a dominant-inhibitory FGF receptor and a dominant-inhibitory retinoic acid receptor suggest that Pax-3 inductive activities arising from Hensen's node and posterior non-axial mesoderm do not strictly depend on FGF or retinoic acid.

Animals↗

PubMed1997

An essential role for retinoid signaling in anteroposterior neural patterning.

The vertebrate central nervous system (CNS) is induced by signals emanating from the dorsal mesoderm, or organizer, that divert the ectoderm away from an epidermal and towards a neural fate. Additional signals from the organizer pattern the neural ectoderm along the anteroposterior axis. We devised highly specific methods utilizing constitutively active or dominant negative receptors to evaluate the role of retinoids in neural patterning. Microinjection of these reagents either augments or reduces retinoid signaling in specific regions of the embryo. We show that increased receptor activity suppresses anterior neural structures while dominant negative receptors lead to anterior enhancement. Similarly, microinjection of the dominant negative receptor leads to the loss of posterior marker genes. We demonstrate that retinoid receptors comprise a critical component in neural posteriorization and are required for proper neuronal differentiation. These results support a quantitative role for retinoid signaling in regionalization of the CNS.

Animals↗

PubMed1997

The Xenopus homolog of Drosophila Suppressor of Hairless mediates Notch signaling during primary neurogenesis.

The X-Notch-1 receptor, and its putative ligand, X-Delta-1, are thought to mediate an inhibitory cell-cell interaction, called lateral inhibition, that limits the number of primary neurons that form in Xenopus embryos. The expression of Xenopus ESR-1, a gene related to Drosophila Enhancer of split, appears to be induced by Notch signaling during this process. To determine how the activation of X-Notch-1 induces ESR-1 expression and regulates primary neurogenesis, we isolated the Xenopus homolog of Suppressor of Hairless (X-Su(H)), a component of the Notch signaling pathway in Drosophila. Using animal cap assays, we show that X-Su(H) induces ESR-1 expression, perhaps directly, when modified by the addition of ankyrin repeats. Using a DNA binding mutant of X-Su(H), we show that X-Su(H) activity is required for induction of ESR-1. Finally, expression of the DNA binding mutant in embryos leads to a neurogenic phenotype as well as increased expression of both X-Delta-1 and XNGNR1, a proneural gene expressed during primary neurogenesis. These results suggest that activation of X-Su(H) is a key step in the Notch signaling pathway during primary neurogenesis in Xenopus embryos.

Animals↗

PubMed1997

The Notch ligand, X-Delta-2, mediates segmentation of the paraxial mesoderm in Xenopus embryos.

Segmentation of the vertebrate embryo begins when the paraxial mesoderm is subdivided into somites, through a process that remains poorly understood. To study this process, we have characterized X-Delta-2, which encodes the second Xenopus homolog of Drosophila Delta. Strikingly, X-Delta-2 is expressed within the presomitic mesoderm in a set of stripes that corresponds to prospective somitic boundaries, suggesting that Notch signaling within this region establishes a segmental prepattern prior to somitogenesis. To test this idea, we introduced antimorphic forms of X-Delta-2 and Xenopus Suppressor of Hairless (X-Su(H)) into embryos, and assayed the effects of these antimorphs on somite formation. In embryos expressing these antimorphs, the paraxial mesoderm differentiated normally into somitic tissue, but failed to segment properly. Both antimorphs also disrupted the segmental expression of X-Delta-2 and Hairy2A, a basic helix-loop-helix (bHLH) gene, within the presomitic mesoderm. These observations suggest that X-Delta-2, via X-Notch-1, plays a role in segmentation, by mediating cell-cell interactions that underlie the formation of a segmental prepattern prior to somitogenesis.

Animals↗

PubMed1996

X-MyT1, a Xenopus C2HC-type zinc finger protein with a regulatory function in neuronal differentiation.

X-MyT1 is a C2HC-type zinc finger protein that we find to be involved in the primary selection of neuronal precursor cells in Xenopus. Expression of this gene is positively regulated by the bHLH protein X-NGNR-1 and negatively regulated by the Notch/Delta signal transduction pathway. X-MyT1 is able to promote ectopic neuronal differentiation and to confer insensitivity to lateral inhibition, but only in cooperation with bHLH transcription factors. Inhibition of X-MyT1 function inhibits normal neurogenesis as well as ectopic neurogenesis caused by overexpression of X-NGNR-1. On the basis of these findings, we suggest that X-MyT1 is a novel, essential element in the cascade of events that allows cells to escape lateral inhibition and to enter the pathway that leads to terminal neuronal differentiation.

Age Factors↗

PubMed1996

Identification of neurogenin, a vertebrate neuronal determination gene.

Several bHLH proteins are involved in vertebrate neurogenesis, but those controlling early stages of neuronal determination have not yet been identified. Here we describe a novel, NeuroD-related bHLH protein, NEUROGENIN, whose expression precedes that of NeuroD in both mouse and Xenopus. Expression of Xenopus NEUROGENIN-related-1 (X-NGNR-1) defines the three prospective territories of primary neurogenesis. Overexpression of X-NGNR-1 (or NEUROGENIN) induces ectopic neurogenesis and ectopic expression of XNeuroD mRNA. Endogenous X-ngnr-1 expression becomes restricted to subsets of cells by lateral inhibition, mediated by X-Delta-1 and X-Notch. The properties of X-NGNR-1 are thus analogous to those of the Drosophila proneural genes, suggesting that it functions as a vertebrate neuronal determination factor.

Amino Acid Sequence↗

PubMed1996

A Xenopus gene, Xbr-1, defines a novel class of homeobox genes and is expressed in the dorsal ciliary margin of the eye.

We have isolated Xbr-1, a novel Xenopus homeobox gene that defines a new class of homeobox genes, distantly related to the Drosophila BarH1 and BarH2 genes. Xbr-1 is predominantly expressed in the developing Xenopus eye, starting as early as the neural plate stage. At early stages of eye development XBR-1 is expressed in the eye vesicle dorsally, in the tissue between the prospective neural retina and pigment epithelium. Later, in the optic cup, it is restricted to the prospective dorsal ciliary margin, an area containing progenitor cells at the edge of retina. Comparing the expression of Xbr-1 in the eye to that of X-Notch-1 suggests that Xbr-1 marks a unique population of pluripotent stem cells within the dorsal ciliary margin. The expression of Xbr-1 and BMP-4 in the dorsal ciliary margin is largely coincident, suggesting that the two molecules interact. We propose that Xbr-1 and BMP-4 may play a role in the development of progenitor cells on the dorsal half of the eye and that they may be involved in the establishment of polarity of the eye along the dorsoventral axis.

Amino Acid Sequence↗

PubMed1996

A posteriorising factor, retinoic acid, reveals that anteroposterior patterning controls the timing of neuronal differentiation in Xenopus neuroectoderm.

During early development of the Xenopus central nervous system (CNS), neuronal differentiation can be detected posteriorly at neural plate stages but is delayed anteriorly until after neural tube closure. A similar delay in neuronal differentiation also occurs in the anterior neural tissue that forms in vitro when isolated ectoderm is treated with the neural inducer noggin. Here we examine the factors that control the timing of neuronal differentiation both in embryos and in neural tissue induced by noggin (noggin caps). We show that the delay in neuronal differentiation that occurs in noggin caps cannot be overcome by inhibiting the activity of the neurogenic gene, X-Delta-1, which normally inhibits neuronal differentiation, suggesting that it represents a novel level of regulation. Conversely, we show that the timing of neuronal differentiation can be changed from late to early after treating noggin caps or embryos with retinoic acid (RA), a putative posteriorising agent. Concommittal with changes in the timing of neuronal differentiation, RA suppresses the expression of anterior neural genes and promotes the expression of posterior neural genes. The level of early neuronal differentiation induced by RA alone is greatly increased by the additional expression of the proneural gene, XASH3. These results indicate that early neuronal differentiation in neuralised ectoderm requires posteriorising signals, as well as signals that promote the activity of proneural genes such as XASH3. In addition, these result suggest that neuronal differentiation is controlled by anteroposterior (A-P) patterning, which exerts a temporal control on the onset of neuronal differentiation.

Animals↗

PubMed1996

Sensitivity of proneural genes to lateral inhibition affects the pattern of primary neurons in Xenopus embryos.

We have compared the roles of XASH-3 and NeuroD, two basic helix-loop-helix transcription factors, in the formation of primary neurons in early Xenopus embryos. When ectopically expressed in Xenopus embryos, XASH-3 and NeuroD induce ectopic primary neurons in very different spatial patterns. We show that the pattern of primary neurons induced by XASH-3 and NeuroD can be accounted for by a difference in their sensitivity to inhibitory interactions mediated by the neurogenic genes, X-Delta-1 and X-Notch-1. Both NeuroD and XASH-3 promote the expression of the inhibitory ligand, X-Delta-1. However, XASH-3 appears to be sensitive to the inhibitory effects of X-Delta-1 while NeuroD is much less so. Consequently only a subset of cells that ectopically express XASH-3 eventually form neurons, giving a scattered pattern, while the ectopic expression of NeuroD leads to a relatively dense pattern of ectopic neurons. We propose that differences in the sensitivity of XASH-3 and NeuroD to lateral inhibition play an important role during their respective roles in neuronal determination and differentiation.

Animals↗

PubMed1995

Primary neurogenesis in Xenopus embryos regulated by a homologue of the Drosophila neurogenic gene Delta.

X-Delta-1, a Xenopus homologue of the Drosophila Delta gene, is expressed in the early embryonic nervous system in scattered cells that appear to be the prospective primary neurons. Ectopic X-Delta-1 activity inhibits production of primary neurons and interference with endogenous X-Delta-1 activity results in overproduction of primary neurons. These results indicate that the X-Delta-1 protein mediates lateral inhibition delivered by prospective neurons to adjacent cells, and that commitment to a neural fate in vertebrates is regulated by Delta-Notch signalling as in Drosophila.

Animals↗

PubMed1995

Xenopus F-cadherin, a novel member of the cadherin family of cell adhesion molecules, is expressed at boundaries in the neural tube.

Development of the vertebrate CNS begins during neurulation when the neural plate gives rise to the neural tube. During neurulation, the different regions of the CNS can be identified in part by the appearance of flexures in the walls of the neural tube. Here we report the isolation and characterization of F-cadherin; a novel member of the cadherin family of cell adhesion molecules, which is expressed at flexures in the neural tube of Xenopus embryos. We show that F-cadherin is first expressed at neural plate stages, that its expression is altered when patterning of the neural tube is perturbed, and that its expression marks boundaries in the neural tube where cell mixing is restricted. These observations suggest that F-cadherin contributes to the regionalization of the neural tube perhaps by mediating differential cell adhesion.

Amino Acid Sequence↗

PubMed1995

Neural induction and neurogenesis in amphibian embryos.

Neural induction has long been known as the process by which the ectoderm of vertebrate embryos initiates neural development. During this inductive interaction, a region of the embryo called the organizer is a source of inducing signals that directs ectoderm away from an epidermal into a neural fate, thereby forming the neural plate and tube. In this review, we will discuss recent progress in characterizing two molecules in Xenopus embryos, noggin and follistatin, which appear to have many of the properties expected of neural inducers produced by the organizer. In addition, we will discuss progress that has been made in characterizing Xenopus homologs of the neurogenic and proneural genes that control the decision between a neural and epidermal fate in the Drosophila embryos. A model is presented in which these genes act downstream of neural induction in vertebrates to control the generation of neural precursor cells during neurogenesis.

Activins↗

PubMed1994

Overexpression of cadherins and underexpression of beta-catenin inhibit dorsal mesoderm induction in early Xenopus embryos.

The cadherin-catenin complex has an important role in cell-cell adhesion and may also function in signaling pathways. We report that overexpression of three cadherin types in Xenopus embryos causes them to develop with reduced dorsal axial structures. The same phenotype is produced in embryos that have been depleted of maternal beta-catenin protein by an antisense oligodeoxynucleotide complementary to beta-catenin mRNA. They show an inhibition in the expression of dorsal mesodermal markers MyoD and goosecoid, but not of ventral and general mesodermal markers. They lack notochords, somites, and neural tubes and are defective in dorsal mesodermal signaling in Nieuwkoop assays. The phenotype can be rescued by the injection of beta-catenin mRNA and not by the injection of Xwnt-8 mRNA. These results show that beta-catenin has an important role in dorsal mesoderm induction. They directly demonstrate the activity of a maternal mRNA in axis specification.

Animals↗

PubMed1994

XASH genes promote neurogenesis in Xenopus embryos.

Neural development in Drosophila is promoted by a family of basic helix-loop-helix (bHLH) transcription factors encoded within the Achaete Scute-Complex (AS-C). XASH-3, a Xenopus homolog of the Drosophila AS-C genes, is expressed during neural induction within a portion of the dorsal ectoderm that gives rise to the neural plate and tube. Here, we show that XASH-3, when expressed with the promiscuous binding partner XE12, specifically activates the expression of neural genes in naive ectoderm, suggesting that XASH-3 promotes neural development. Moreover, XASH-3/XE12 RNA injections into embryos lead to hypertrophy of the neural tube. Interestingly, XASH-3 misexpression does not lead to the formation of ectopic neural tissue in ventral regions, suggesting that the domain of XASH proneural function is restricted in the embryo. In contrast to the neural inducer noggin, which permanently activates the NCAM gene, the activation of neural genes by XASH-3/XE12 is not stable in naive ectoderm, yet XASH-3/XE12 powerfully and stably activates NCAM, Neurofilament and type III beta-tubulin gene expression in noggin-treated ectoderm. These results show that the XASH-3 promotes neural development, and suggest that its activity depends on additional factors which are induced in ectoderm by factors such as noggin.

Animals↗

PubMed1994

Selective disruption of E-cadherin function in early Xenopus embryos by a dominant negative mutant.

E-cadherin function was disrupted in vivo in developing Xenopus laevis embryos through the expression of a mutant E-cadherin protein lacking its cytoplasmic tail. This truncated form of E-cadherin was designed to act as a dominant negative mutant by competing with the extracellular interactions of wild-type endogenous E-cadherin. Expression of truncated E-cadherin in the early embryo causes lesions to develop in the ectoderm during gastrulation. In contrast, expression of a similarly truncated N-cadherin protein failed to cause the lesions. The ectodermal defect caused by the truncated E-cadherin is rescued by overexpression of wild-type E-cadherin, by co-injection of full-length E-cadherin RNA along with the RNA for the truncated form. Overexpression of full-length C-cadherin, however, is unable to compensate for the disruption of E-cadherin function and can actually cause similar ectodermal lesions when injected alone, suggesting that there is a specific requirement for E-cadherin. Therefore, E-cadherin seems to be specifically required for maintaining the integrity of the ectoderm during epiboly in the gastrulating Xenopus embryo. Differential cadherin expression reflects, therefore, the requirement for distinct adhesive properties during different morphogenetic cell behaviors.

Amino Acid Sequence↗

PubMed1993

Xenopus Distal-less related homeobox genes are expressed in the developing forebrain and are induced by planar signals.

The polymerase chain reaction (PCR) was used to isolated five Xenopus homeobox clones (X-dll1 to 5) that are related to the Drosophila Distal-less (Dll) gene and we propose a subdivision of the vertebrate distal-less gene family according to sequence similarities. cDNA clones were isolated for X-dll2, 3 and 4, and their expression was studied by RNase protection and in situ hybridization. X-dll2, which belongs to a separate subfamily than X-dll3 and 4, is not expressed in the neural ectoderm. X-dll3 and X-dll4, which belong to the same subfamily, have a similar but not identical pattern of expression that is restricted to anterior ectodermal derivatives, namely the ventral forebrain, the cranial neural crest and the cement gland. X-dll3 is also expressed in the olfactory and otic placodes while X-dll4 is expressed in the developing eye. X-dll3 differs from the other Xenopus genes and the previously isolated Dll-related mouse genes, in that localized expression can be detected by in situ hybridization very early in development, in the anterior-transverse ridge of the open neural plate. Based on that early expression pattern, we suggest that X-dll3 marks the rostral-most part of the neural plate, which gives rise to the ventral forebrain. Finally, we have used these Xenopus distal-less genes to show that the anterior neural plate can be induced by signals that spread within the plane of neural ectoderm, indicating that at least the initial steps of forebrain development do not require signals from underlying mesoderm.

Amino Acid Sequence↗