Onset of expression of the alpha subunit of Ca2+/calmodulin-dependent protein kinase II and a novel related protein in the developing retina.

Calcium-calmodulin-dependent protein kinase II is an abundant protein in the nervous system and has been associated with many aspects of neuronal function, including events related to synaptic transmission. The purpose of this study is to correlate the onset of expression of this kinase with a specific developmental event in retinal morphogenesis using a monoclonal antibody to the 50-kDa alpha-subunit. Microscopy showed the antigen to be associated with the plexiform layers of the retina. Western blots demonstrated that the onset of expression of the alpha-subunit coincided in time with the initial formation of the plexiform layers. However, the onset of expression of the 50-kDa alpha-subunit was preceded by the earlier embryonic appearance of a related 82.5-kDa antigen that was recognized by the antibody. The amount of this latter protein declined as the amount of the alpha-subunit increased in retinal homogenates. Although this related 82.5 kDa protein disappeared from blots of retinal homogenates after embryonic d 14, it could be detected in concentrated supernatant fractions isolated from the retinae of hatched chicks. Microscopy showed that a subset of retinal cells and their processes contained this antigen in early embryonic chicks. Finally, the 50 kDa alpha-subunit of kinase II and the 82.5 kDa novel antigen were shown to be separable by differential centrifugation.