The origin and development of retinal pigment cells and melanophores analyzed by Xenopus black-white chimeras.

At the 16 cell stage, three kinds of borealis-laevis and eight kinds of laevis-laevis chimeric embryos were produced by replacing a particular blastomere of albino embryos of Xenopus laevis with that of wild-type embryos of X. borealis or X. laevis, and then leaving the embryos to develop into frogs.

A Novel Monoclonal Antibody disrupting Cell Type Specific Substratum Adhesion of Frog (Xenopus laevis) Epithelial Cells and Endothelial Cells: (frog, Xenopus laevis/cell substratum adhesion/cell adhesion/endothelial cells).

We isolated a mouse monoclonal antibody (FAD-II) that disrupts cell-substratum adhesion of amphibian (Xenopus laevis) epithelial cells and endothelial cells. The effect of the antibody was cell-type specific, and the antibody had no effect on fibroblastic cells while fibronectin peptide blocked cell-substratum adhesion of all the cell types examined. In developing frog embryos, the epitopes recognized by the antibody were detected in pronephrotic ducts and in other tissue cells of embryos (from stage 33/34 afterwards).

Regulation of the Dorsal Axial Structures in Cell-Deficient Embryos of Xenopus laevis: (regulation/Xenopus laevis/cell-deficient embryo/dorsal axial structures).

To study the regulation of the dorsal axial structures, we removed the right animal dorsal and the right vegetal dorsal cells from an 8-cell embryo of Xenopus laevis. Most of the right dorsal cell-deficient embryos developed to normally proportioned tailbud embryos. No detectable delay was observed in their development.

Mobilization of newly synthesized RNAs into polysomes inXenopus laevis embryos.

The mobilization of newly synthesized 18S and 28S rRNAs, 4S RNA and poly(A) RNA into polysomes was studied in isolated cells ofXenopus laevis embryos between cleavage and neurula stages. Throughout these stages, 4S RNA and poly(A) RNA were mobilized immediately following their appearance in the cytoplasm. 18S rRNA however, stayed in the ribosomal subunit fraction for about 30 min until the 28S rRNA appeared, when the two rRNAs were mobilized together at an equimolar ratio.

REGULATION OF RIBOSOMAL RNA SYNTHESIS DURING TAIL REGRESSION IN ORGAN CULTURE.

Tail tips of early prometamorphic larvae of Xenopus laevis were organ-cultured in Stearns' solution. Triiodothyronine induced a number of responses characteristic of metamorphosis, such as regression, decrease in DNA and RNA content, and increase in H-uridine incorporation into RNA. The synthesis of ribosomal RNAs and its degradation in regressing tail tips were studied.