AbstractsBiology & Animal Science

Myelin formation in the chick embryo sciatic nerve was examined during development by analysis of three myelin lipids (cholesterol, phospholipids, and cerebrosides) and of a myelin related enzyme (2', 3'-cyclic AMP 3'-phosphohydrolase). The role of the Schwann cell in controlling the synthesis of these myelin components was studied by in vitro techniques and by chemical interference of myelination. The fourteenth day of embryo incubation was found to mark the onset of rapid myelin deposition which continued throughout in ovo development. In vitro experiments revealed that sciatic nerve trunks (from embryos younger than 16 days) cultured in the absence of nerve cell nuclei were capable of myelinating for up to 48 hours. Chemical stimulation of Schwann cell RNA and protein synthesis by 1,1,3-tricyano-2-amino-l-propene (Triap) showed that this compound enhanced sciatic nerve 2', 3'-cyclic AMP 3'-phosphohydrolase (cAMPase) activity. Within 24 hours following in ovo injections of 0.2 mg of Triap, 13 day old embryos exhibited a three-fold increase in cAMPase activity and a 50% increase in cerebroside accumulation. Enzyme analysis and in vitro incorporation of d,l-leucine-l-¹⁴C into nerve protein suggested that Triap stimulated de novo synthesis of the myelin enzyme. Aside from a slight increase in aldolase activity, no other nerve protein, myelin component, or embryonic nerve tissue studied exhibited an increase due to the presence of Triap. The effect of Triap on Schwann cell RNA synthesis was examined by in vitro incorporation of uridine-5-³H and subsequent analysis of rapidly labeled RNA by polyacrylamide gel electrophoresis. Triap was found to alter the rate at which rapidly labeled RNA was synthesized in ovo and in vitro. From the results of these and preliminary experiments with actinomycin D and cycloheximide it was proposed that Triap enhances sciatic nerve myelin synthesis at the level of Schwann cell transcription. The mechanism by which Triap influences myelination in the chick embryo and the significance of increased peripheral nerve cAMPase activity were discussed. The possibility that Triap affects nervous tissue protein synthesis via the endocrine system was also presented.