Characterization and early embryonic expression of a neural specific transcription factor xSOX3 in Xenopus laevis.

Using the powerful RDA-PCR-technique we could identify a novel Xenopus specific Sox-gene (xSox3) a transcription factor closely related to the sox sub-group B, which contains a HMG box. In normogenesis the xSox3 gene is expressed in the presumptive central nervous system. Furthermore a maternal component is also found in oocytes and in early cleavage stages in the animal hemisphere only.

Partially purified factor from embryonic chick brain can provoke neuralization of Rana temporaria and Triturus alpestris but not Xenopus laevis early gastrula ectoderm.

A high neuralizing activity has been determined in forebrain of 7.5-day old chick embryos using Rana temporaria early gastrula ectoderm as reacting tissue (Mikhailov and Gorgolyuk, Soviet Scientific Reviews, Section of Physiology and General Biology, Vol. 1: 267-306, 1987).

Extracellular matrix components prevent neural differentiation of disaggregated Xenopus ectoderm cells.

Neuralization (archencephalic brain formation) takes place after dissociation and delayed reaggregation of animal caps of early gastrula without inducer (Grunz, H. and L. Tacke: Cell Differ.

Neural differentiation of Xenopus laevis ectoderm takes place after disaggregation and delayed reaggregation without inducer.

When Xenopus blastula or early gastrula ectoderm is disaggregated and cells are kept dispersed for up to 5 h prior to reaggregation, the resulting spheres will differentiate into large neural structures. In contrast, dissociated and immediately reaggregated ectoderm will only differentiate into ciliated epidermis (so-called 'atypical epidermis'). Ectoderm treated with mesoderm-inducing XTC-conditioned medium during the period of reaggregation immediately after disaggregation will only form one- or two-cell types (notochord and somites) only.

A mesoderm-inducing factor from a Xenopus laevis cell line : Chemical properties and relation to the vegetalizing factor from chicken embryos.

We have compared the chemical properties and biological activities of the mesoderm-inducing factor that is secreted by the Xenopus XTC cell line with the vegetalizing factor from chicken embryos. The inducing activity of the factors was tested in different concentrations on totipotent ectoderm either by implantation into early gastrulae of Triturm alpestris or by application of solutions to isolated ectoderm of early gastrulae of Xenopus laevis. Both factors have similar properties.

Close juxtaposition between inducing chordamesoderm and reacting neuroectoderm is a prerequisite for neural induction in Xenopus laevis.

The results of this study indicate that the induction of the central nervous system in Xenopus laevis depends on the close juxtaposition of inducing chordamesoderm and reacting ectoderm, which is necessary for the short distance migration of neural inducing factors. The examination of the neuroectoderm-chordamesoderm interface at intervals of 1 h up to 5 h showed that the onset of neural induction is correlated to the degree of contact formation between ectodermal and mesodermal cells. In the ectoderm cells the number of coated pits, a feature of receptor-mediated endocytosis, is increased.

The inducing capacity of the presumptive endoderm of Xenopus laevis studied by transfilter experiments.

The inducing capacity of the vegetal hemisphere of early amphibian blastulae was studied by placing a Nucleopore filter (pore size 0.4 μm) between isolated presumptive endoderm and animal (ectodermal) caps. The inducing effect was shown to traverse the Nucleopore membrane.

Electron microscope study of the binding of Con A-gold to superficial and inner ectoderm layers ofXenopus laevis and its relation to the neural-inducing activity of this lectin.

Isolated competent amphibian ectoderm differentiates into neural (archencephalic) structures when treated with the plant lectin concanavalin A (Con A). While the inner ectoderm layer ofXenopus laevis forms brain structures after incubation with Con A, the outer ectoderm layer differentiates into ciliated epidermis only. This difference can be correlated with the pattern of Con A bound to the plasma membrane.