ACCUMULATION IN FETAL MUSCLE AND LOCALIZATION TO THE NEUROMUSCULAR-JUNCTION OF CAMP-DEPENDENT PROTEIN-KINASE-A REGULATORY AND CATALYTIC SUBUNITS RI-ALPHA AND C-ALPHA

Using probes specific for cAMP-dependent protein kinase, we have analy zed by in situ hybridization the patterns of expression of regulatory and catalytic subunits in mouse embryos and in adult muscle. RI alpha transcripts are distributed in muscle fibers exactly as acetylcholines terase, showing that this RNA is localized at the neuromuscular juncti on. The transcript levels increase upon denervation of the muscle, but the RNA remains localized, indicating a regulation pattern similar to that of the epsilon subunit of nicotinic acetylcholine receptor. RI a lpha transcripts have accumulated in the muscle by day 12 of mouse emb ryogenesis, and localization is established by day 14, at about the ti me of formation of junctions. This localization is maintained througho ut development and in the adult. Immunocytochemical analysis has demon strated that RI alpha protein is also localized. In addition, RI alpha recruits C alpha protein to the junction, providing at this site the potential for local responsiveness to cAMP, PKA could be implicated in the establishment and/or maintenance of the unique pattern of gene ex pression occurring at the junction, or in the modulation of synaptic a ctivity via protein phosphorylation. Embryonic skeletal muscle shows a high level of C alpha transcripts and protein throughout the fiber; t he transcripts are already present by day 12 of embryogenesis, and the ir elevated level is maintained only through fetal life, In the adult, the C alpha hybridization signal of muscle is weak and homogeneous.