PROTEIN KINASE-C-EPSILON IS A DEVELOPMENTALLY-REGULATED, NEURONAL ISOFORM IN THE CHICK-EMBRYO CENTRAL-NERVOUS-SYSTEM

Protein kinase C (PKC) is expressed as many isoforms and in high quant ities in the central nervous system (CNS), which suggests an important role for this enzyme in neuronal development and function. We used sp ecific antibodies to investigate the expression of the known PKC isofo rms in extracts from chick major CNS areas during embryogenesis, from day 3 (E3) of incubation to day 1 post-hatching (P1). PKC-epsilon was the predominant isoform and was expressed from E6 onward in all brain regions, except retina (E12 and on). PKC-alpha/beta and -zeta isoforms were expressed at lower levels prior to PKC-epsilon expression and th roughout embryogenesis. No other isoforms were detected in neural tiss ue preparations. We then used neural culture systems derived from the chick CNS to study the expression of PKC isoforms in neuroblasts, cort ical neurons, and cortical glial cells. Western blotting and immunosta ining of neuroblast-enriched cultures, derived from E3 CNS, showed onl y the Ca2+-dependent PKC-alpha/beta to be present. Studies on neuronal cultures derived from E6 cerebral hemispheres revealed only the Ca2+- independent PKC-epsilon to be expressed in neurons, as predicted by th e developmental studies on tissue homogenates. PKC-epsilon immunoreact ivity was seen intracellularly in differentiating neurons, regardless of their neurotransmitter phenotypes, and it correlated well with the level of neuronal activity. Furthermore, PKC-alpha/beta immunoreactivi ty was verified on glia cells, as the glial lineage emerges in E15 cor tical cultures. These data suggest that PKC-epsilon expression is asso ciated with the final neuroblast division in neurons, and the correlat ion of PKC isoform expression and neural cell lineage is discussed. (C ) 1993 Wiley-Liss, Inc.