Studies on Polyadenylic Acid‐Containing RNA from Developing Nervous System of the Chicken the

To investigate certain biochemical aspects of myelination, a study was undertaken of the messenger‐like RNA in the nervous system of pre‐ myelinating 14‐day embryos and of myelinating 17‐day embryos and 3‐day chicks. The central and peripheral nervous systems of the chick were found to contain and to actively synthesize poly(A) + RNA. RNA species binding to oligo(dT)‐cellulose contained a relatively high proportion of adenylate residues and were resistant to the actions of pancreatic and T 1 ribonucleases. Preparations labeled by incubation with adenosine in vitro showed a decrease in the proportion of poly(A) + RNA as the age of the animal increased, while preparations labeled in vivo exhibited the opposite trend. Polyacrylamide gel electrophoretograms of both in vivo and in vitro labeled pqeparations showed that the poly(A) + fractions contained mainly heterodisperse RNA species. The average molecular size of poly(A) + RNAs of purified polysomal fractions of nerve RNA from 3‐day chicks was smaller than 18S, whereas that of total poly(A) − RNA was larger than 18s. The proportion of poly(A) + molecules larger than 18s was lower in the rapidly myelinating nerve tissues of 17‐day embryos and post‐hatching chicks than in those of premyelinating 14‐day embryos. Similar results were obtained for crude nuclear RNA fractions or RNA preparations fractionated under denaturing conditions. These results are consistent with previous work showing that the embryonic peripheral nerve contains a larger proportion of high‐molecular‐weight, messenger‐like RNA molecules than does nerve tissue from young chicks or adults.