EXPRESSION OF MESSENGER-RNA FOR A NEURONAL DIFFERENTIATION FACTOR, TA20, IN DEVELOPING RAT BRAINS

In our previous study, a novel factor, TA20, was isolated from NG108-1 5 cells. The TA20 mRNA was increased by stimulation which also induced neuronal differentiation. Neuronal cells overexpressed with TA20 exte nded long neurites and stopped cell growth (Tohda et al., 1995, Neuros ci. Res., 23: 21-27). We investigated the expression pattern of TA20 m RNA in developing rat brains to predict physiological roles of TA20. T A20 mRNA began to increase between embryonic days 13 and 16. TA20 mRNA was observed mainly in neocortical, hippocampal and precerebellar neu roepithelium on embryonic day 16. Although the level of TA20 mRNA in t he cerebral cortex was higher before birth than after birth, the level in cerebellar Purkinje cells increased gradually even after birth. Th e high expression level of TA20 mRNA in the hippocampus was maintained before and after birth. Thus, TA20 was expressed highly in brain regi ons in which neurons were changing morphologically and qualitatively, suggesting that TA20 may be involved in neuronal formation in vivo.