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 quantities in the central nervous system (CNS), which suggests an important role for this enzyme in neuronal development and function. We used specific antibodies to investigate the expression of the known PKC isoforms 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 throughout embryogenesis. No other isoforms were detected in neural tissue preparations. We then used neural culture systems derived from the chick CNS to study the expression of PKC isoforms in neuroblasts, cortical neurons, and cortical glial cells. Western blotting and immunostaining of neuroblast-enriched cultures, derived from E3 CNS, showed only the Ca(2+)-dependent PKC-alpha/beta to be present. Studies on neuronal cultures derived from E6 cerebral hemispheres revealed only the Ca(2+)-independent PKC-epsilon to be expressed in neurons, as predicted by the developmental studies on tissue homogenates. PKC-epsilon immunoreactivity 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 immunoreactivity was verified on glia cells, as the glial lineage emerges in E15 cortical cultures. These data suggest that PKC-epsilon expression is associated with the final neuroblast division in neurons, and the correlation of PKC isoform expression and neural cell lineage is discussed.