HETEROGENEOUS EXPRESSION OF THE POLYSIALYLTRANSFERASES ST8SIA-II AND ST8SIA-IV DURING POSTNATAL RAT-BRAIN DEVELOPMENT

Polysialic acid on the neural cell adhesion molecule is developmentall y regulated and has been implicated in the plasticity of cell-cell int eractions. The sialyltransferases ST8Sia II and ST8Sia IV are able to catalyze the synthesis of polysialic acid. This study compares the exp ression of ST8Sia II and ST8Sia IV mRNA during postnatal rat brain dev elopment. Northern blot analysis indicated a substantial down-regulati on of ST8Sia II from high expression at postnatal day 2 to almost unde tectable levels at the age of 6 months. In contrast, the decline of ST 8Sia IV content was moderate. In the mature brain, ST8Sia IV is the pr edominant polysialyltransferase. In situ hybridization of selected bra in regions at postnatal days 2, 11, and 21 confirmed the decline of ST 8Sia II level in isocortex, hippocampus, and cerebellum. ST8Sia II was not detectable at any time point in the subependymal layer and the la yers of the olfactory bulb. Persistent ST8Sia IV expression was locali zed in the subependymal layer, the glomerular layer of the olfactory b ulb, and the granule cell layer of the dentate gyrus and in some widel y dispersed cells of the isocortex. The distinct expression patterns o f ST8Sia II and ST8Sia IV suggest their differential regulation. As di scussed with regard to the persistent polysialic acid expression, ST8S ia IV should receive particular attention in the mature brain.