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R Winklbauer

Publications and source records attributed to R Winklbauer.

10 recordsLinked to original sources
PubMed1992

Cell interaction and its role in mesoderm cell migration during Xenopus gastrulation.

In the Xenopus gastrula, the mesoderm moves as a coherent cell aggregate across the blastocoel roof toward the animal pole. We show that the cohesion of the mesoderm is not only mechanically necessary, but that aggregate formation has profound effects on the migratory behavior of mesoderm cells. Whereas isolated mesoderm cells are bi- or multipolar, move stepwise and change their direction of movement frequently, aggregated mesoderm cells migrating on their in vivo substrate appear unipolar and move continuously and persistently. Moreover, only mesoderm cell aggregates, but not single cells, can follow guidance cues present in the extracellular matrix of the blastocoel roof substrate. Thus, the cohesion of the mesodermal cell mass is an essential feature of mesoderm migration during Xenopus gastrulation. We show that the Ca(2+)-dependent cell adhesion molecule U-cadherin is involved in mediating this cohesion.

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PubMed1992

Motile behavior and protrusive activity of migratory mesoderm cells from the Xenopus gastrula.

During Xenopus gastrulation, the mesoderm migrates across a fibronectin (FN)-containing substrate, the inner surface of the blastocoel roof (BCR). A possible role for FN is to promote the extension of cytoplasmic processes which serve as locomotory organelles for mesoderm cells. To test this idea, the interaction of prospective head mesoderm (HM) cells with FN was examined in vitro. Nonattached HM cells extend filiform processes from an active region of the cell surface. This spontaneous activity is modulated by cell attachment to FN. Additional active regions appear, and cytoplasmic lamellae extend from these sites, leading to cell spreading and translocation. Thus, although FN seems not to induce processes de novo, it modulates a spontaneous protrusive activity to yield the extension of lamellae along the substrate surface. As putative locomotory organelles, HM cell protrusions were characterized functionally. They adhere rapidly and selectively to in situ substrates, preferentially to FN, and retract upon attachment. During translocation, the passive cell body is moved by the activity of the protrusions. Lamellae continuously extend, retract, or split into parts. This leads to an intermittent, nonpersistent mode of translocation. The polarity of HM cells, as expressed in the arrangement of protrusions, bears no constant relationship to the orientation of the cell body, and a cell can change its direction of movement without a corresponding rotation of the cell body. This may be relevant with respect to the mechanism by which mesoderm cells translate guidance cues of the BCR into a polarized, oriented cell structure during directional migration in situ.

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PubMed1991

Directional mesoderm cell migration in the Xenopus gastrula.

The movement of the dorsal mesoderm across the blastocoel roof of the Xenopus gastrula is examined. We show that different parts of the mesoderm which can be distinguished by their morphogenetic behavior in the embryo are all able to migrate independently on the inner surface of the blastocoel roof. The direction of mesoderm cell migration is determined by guidance cues in the extracellular matrix of the blastocoel roof and by an intrinsic tissue polarity of the mesoderm. The mesodermal polarity shows the same orientation as the external guidance cues and is strongly expressed in the more posterior mesoderm. The guidance cues of the extracellular matrix are recognized by all parts of the dorsal mesoderm and even by nonmesodermal cells from other regions of the embryo. The extracellular matrix consists of a network of fibronectin-containing fibrils. The adhesiveness of this matrix does not vary along the axis of mesoderm movement, excluding haptotaxis as a guidance mechanism in this system. However, an intact fibronectin fibril structure is necessary for directional mesoderm cell migration. When the assembly of fibronectin into fibrils is inhibited, mesoderm explants still migrate on the amorphous extracellular matrix, but no longer directionally. It is proposed that polarized extracellular matrix fibrils may normally guide the migrating mesoderm to its target region.

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PubMed1990

Mesodermal cell migration during Xenopus gastrulation.

The adhesive glycoprotein fibronectin (FN), which is a component of the network of extracellular matrix fibrils on the inner surface of the blastocoel roof (BCR), has been proposed to play a major role in directing mesodermal cell migration during amphibian gastrulation. In the first part of this paper, the adhesion of Xenopus mesodermal cells to FN in vitro is examined. Cells from several mesoderm regions, which differ in developmental fate and morphogenetic activity, are able to bind specifically to the RGD cell-binding site of FN. Dorsal mesodermal cell adhesion to FN varies along the anterior-posterior (a-p) axis: adhesion is strongest in the anterior head mesoderm, and gradually decreases posteriorly. This a-p gradient of mesodermal adhesiveness to FN does not change during mesodermal involution, and is reflected in the morphology of mesodermal explants on FN. An a-p strip of mesoderm develops a spreading, leading anterior margin and a compact, retracting posterior end, thus moving slowly and directionally over the FN substrate at about 0.8 micron/min. Although dissociated cells from all levels of the dorsal mesodermal axis adhere to FN, only the anterior, leading prospective head mesoderm cells migrate as single cells on a FN substrate in vitro. Locomotion by means of lamelliform protrusions occurs at an average rate of about 1.5 micron/min. Cells of the more posterior axial mesoderm merely shift position at random without substantial net translocation, and preinvolution mesoderm cells are completely stationary. On the BCR, the in vivo substrate for mesodermal cell migration, dissociated prospective head mesoderm cells spread and migrate as on FN in vitro, at 2.2 microns/min. In the presence of an RGD peptide which inhibits cell-FN interaction, cells remain globular and do not spread. They are still motile, but change direction frequently, which leads to less efficient net translocation. Apparently, interaction with the RGD cell-binding site of FN and concomitant spreading of head mesoderm cells is required for the stabilization of cell locomotion. In contrast to the directional migration of the mesoderm cell population toward the animal pole in the embryo, the pathways of dissociated cells on the BCR are randomly oriented. Coherent explants of migratory mesoderm do not move at all on the BCR, although they translocate on FN in vitro.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1989

Development of the lateral line system in Xenopus.

The lateral line system of fishes and amphibians consists of numerous epidermal mechano-receptors which are distributed over the whole body surface. As in other amphibians, the lateral line system of Xenopus develops from epidermal placodes situated on the head region of the embryo. The dorsolateralis placodes form a rostro-caudal series of epidermal thickenings centered around the otic placode. In this series, placodes remaining within the epidermis and forming lateral line primordia alternate with lateral line ganglion forming placodes. Each lateral line primordium elongates and migrates within the epidermis along a well-defined pathway, leaving behind a row of small cell groups, the primary lateral line organs. As the ganglion which supplies a given row of organs and the corresponding lateral line primordium originate in spatial contiguity, and as the axons of the lateral line nerve grow out together with the migrating primordium, the lateral line neurones remain in contact with their target cells throughout development. After segregation of a primary organ from a migrating primordium, cell differentiation occurs. Receptor cells establish afferent and efferent synaptic contacts with axons from the lateral line nerve. Apically, a bundle of stereocilia and a single, microtubule-containing kinocilium protrude from the surface of a receptor cell into a jelly-like cupula, which extends into the surrounding fluid. Displacement of the cupula and the concomitant bending of the cilia stimulates the receptor cells. The cilia of a receptor cell are asymmetrically arranged, and this structural polarity is related to the directional sensitivity of the cells. Two types of receptor cells, with opposite orientations, are intermingled within each organ, giving the whole organ a bidirectional sensitivity. The number of lateral line organs is increased by the process of accessory organ formation, where primary organs grow and divide to produce secondary organs. In this way, existing rows of organs are extended. Moreover, single primary organs are transformed into elongate plaques of closely apposed organs. The lateral line system has reached its greatest extent at late larval stages. During metamorphosis, the number of organ plaques is reduced in some lines, and one line even disappears completely. Two large, myelinated afferent fibers innervate a whole organ plaque. They branch repeatedly to supply every organ of the plaque, and each fiber is thought to innervate only receptor cells of the same polarity.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1988

Differential interaction of Xenopus embryonic cells with fibronectin in vitro.

Two distinct cell types from the amphibian gastrula were compared with regard to their interactions in vitro with fibronectin (FN). Xenopus embryonic endoderm cells attach to FN substrates in a way characteristic of most cell types studied so far; that is, adhesion increases abruptly at a certain threshold concentration of FN, and maximal binding of cells already occurs at low FN concentrations (10 micrograms/ml). In contrast, embryonic ectodermal cells bind maximally to FN substrates only at unusually high concentrations of FN (200 micrograms/ml). This peculiar mode of attachment to FN has been characterized more closely. It is shown that the adhesion of ectodermal cells is modified by their interaction with a heparin-binding domain of the FN molecule. Furthermore, ectodermal cell adhesion increases very slowly with increasing FN concentrations. Despite these characteristic differences, both ectodermal and endodermal cells attach to the normal RGD cell-binding site of FN, as can be shown by competitive inhibition of adhesion by a hexapeptide containing the RGD sequence of amino acids.

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PubMed1986

Cell proliferation in the ectoderm of the Xenopus embryo: development of substratum requirements for cytokinesis.

The requirements for cell division in ectodermal blastomeres of the early Xenopus embryo were studied. Isolated blastomeres divide autonomously on nonadhesive agar in a simple salt solution up to the midblastula stage. After the midblastula transition, cell-cell contact is required for blastomere division. In isolated blastomeres of that stage, cytokinesis fails, but nuclear division continues normally for some time. Cell-cell contact as a prerequisite for blastomere division can be replaced by culturing blastomeres on an appropriate substratum. Clonal growth of isolated blastomeres is supported by a variety of protein substrata, indicating rather unspecific substratum requirements. Different substrata which do not support blastomere division can affect different steps in cytokinesis.

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PubMed1985

Development of the lateral line system in Xenopus laevis. III. Development of the supraorbital system in triploid embryos and larvae.

During normal development of the supraorbital lateral line system of Xenopus, an elongated streak of primordial cells becomes subdivided into a linear series of cell groups containing only about eight cells each, thus forming a row of primary lateral line organs (Winklbauer & Hausen, 1983a,b). In triploid Xenopus embryos, cell size is 1.5 X normal. When the formation of lateral line organs occurs in triploid primordia, the nascent organs contain only about five or six cells each, i.e. about two thirds of normal. Thus, the increase in cell size is compensated for by a corresponding reduction in cell number, keeping constant the organ size in terms of total cell mass or volume. This result excludes a cell counting mechanism for determining organ size. In diploids, the primary organs, although being of equal size initially, differ vastly in their final size and exhibit a peculiar frequency distribution of organ sizes. A detailed quantitative model for supraorbital lateral line development has been proposed, which accounts for this characteristic frequency distribution (Winklbauer & Hausen, 1983b). This model makes precise predictions as to the frequency distribution of the final size of triploid lateral line organs, where the initial organ size is reduced to five or six cells. These predictions were verified experimentally.

Animals↗
PubMed1985

Development of the lateral line system in Xenopus laevis. IV. Pattern formation in the supraorbital system.

The periodic pattern of the supraorbital lateral line organs forms in the epidermis of Xenopus by the subdivision of a streak-like primordium into a linear series of small cell groups. In normal development, each such organ initially contains about 8 cells (Winklbauer & Hausen, 1983a,b). To see whether this initial organ size depends on the size of the streak-like primordium at the time of organ segregation, primordium size was reduced experimentally before the onset of pattern formation. In such small primordia, the size of the primary organs formed is not adjusted so as to allow the formation of a normal number of organs. Instead, the initial organ size is kept approximately normal, and the number of organs is correspondingly reduced, i.e. the pattern forming mechanism is not capable of 'size regulation'.

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