Developmental expression of the RI subunit of cyclic AMP-dependent protein kinase in retina

Type I and type II isoenzymes of cyclic AMP-dependent protein kinase were identified by anion exchange chromatography and immunoblotting in human retina at various stages of development. The type I form was typical of the early fetal stage during which proliferation and migration were the primary cellular processes. In later stages of differentiation and maturation, RI was no longer detected: the RII isoform, which appeared at the end of the proliferative phase, being the only isoform seen in mature retina, with a doubling of the specific activity of cyclic AMP-dependent protein kinase. Northern blot analyses showed that an RI transcript of 4.5 kb was present not only in fetal but also in mature human retina. The RI transcript was also found in fetal and adult bovine retina and in adult monkey retina. In vitro translation of mature retinal RNA produced a protein identical in size to authentic RI which was precipitated by anti-RI antiserum. Expression of RI in retina thus appears to be regulated during development. The presence of the mRNA for the RI subunit in the adult retina suggests that the regulation might be post-transcriptional.