Differential expression and subcellular localization for subunits of cAMP-dependent protein kinase during ram spermatogenesis

Abstract

The expression of mRNAs for the RI(α), RII(α) and C(α) subunits of cAMP-dependent protein kinase has been studied in different ram germ cells. The sizes of the specific RI(α), RII(α), and C(α) mRNAs, observed in germ cells were 1.6, 2.0, and 2.6 kb, respectively. RI(α) and C(α) mRNAs were mainly expressed in primary spermatocytes. A postmeiotic expression predominating in early spermatids was unique to RII(α) mRNA. The location of RI, RII(α), and C subunits in well-defined organelles of ram spermatids and epididymal sperm was assessed by immunogold electron microscopy. In spermatids, RI, RII(α), and C were essentially present in the forming acrosome and, to a lesser extent, in the nucleus. During sperm epididymal maturation, the protein kinases disappeared from the acrosome and were detected in a variety of sperm functional areas, such as the tip of the acrosome, the motility apparatus, and the membrane network. The present study on subunits of cAMP-dependent protein kinase supports the concept that specific functions are attached to the different subunits in that it shows differential expression and differential subcellular localization in germ cells.