Changes in nucleic acid distribution during neural-tube formation in amphibian embryos

Abstract

1. 1. Amphibian embryos which exhibit accelerated neural-tube formation and an excess total-RNA synthesis after treatment with nucleotide solutions have now been examined for changes of labeled nucleic acid distribution among the cell particulates. 2. 2. Embryos treated with solutions of [ 14C]adenine nucleotides rapidly incorporate labeled precursors into nuclear RNA and DNA fractions between the end of gastrulation and the start of neural-tube formation in both continuous treatment and in pulse-chase experiments. 3. 3. During neural-tube closure there is a loss of labeled material from the nuclear RNA and “DNA fractions”, and a simultaneous increase in the labeling of microsomal and cytoplasmic non-particulate fractions. 4. 4. The “DNA fraction” contains about 10% of the total nuclear RNA (not extractable by the usual HClO 4 or KOH methods), and some contaminating protein. RNA fractions are apparently pure. 5. 5. Pre-labeling of embryos with 32P shows the same loss of radioactivity from nuclear RNA and “DNA fractions” and corresponding increase in labeling of microsomes and non-particulate fractions during neural-tube formation, whether the neural-tube closure proceeds normally with time, or is accelerated by addition of unlabeled ATP to solutions. The changes in labeling of nucleic acid materials is apparently related to the formation of the neural tube. 6. 6. An effective method of preparation of HClO 4 extracts for 14C counting is described.