Patterns of macromolecule synthesis during development of Xenopus laevis: I. Incorporation of radioactive precursors into dissociated embryos

Abstract

Xenopus laevis embryos may be dissociated within their vitelline membranes. Such dissociated embryos are highly permeable to nucleosides and amino acids and can therefore be used effectively for short-term labeling experiments. The high permeability lasts for at least 5 hours, during which time the patterns of RNA and protein synthesis are like those in ordinary (but far less permeable) embryos. The dissociated embryos eventually reaggregate and undergo limited histogenesis. Their patterns of RNA synthesis change in the normal way. Pulse-labeling with uridine- 14C in postgastrula stages yields a 40 S nuclear RNA. Its maturation is shown (in studies to be reported separately) to produce the cytoplasmic 28 S and 18 S species. Blastula and cleavage stages synthesize heterogeneous nonribosomal RNA and much more low molecular weight material sedimenting at about 4 S. Media conditioned by the presence in them of blastula cells, and cell sap from cleavage stages, were tested for factors capable of inhibiting specifically the synthesis of 28 S and 18 S RNA or their precursors. No such specific inhibitory factors were detected in these studies.