Subunits of Cyclic Adenosine 3′,5′-Monophosphate-Dependent Protein Kinase Show Differential and Distinct Expression Patterns during Germ Cell Differentiation: Alternative Polyadenylation in Germ Cells Gives Rise to Unique Smaller-Sized mRNA Species1

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Abstract
Cyclic AMP (cAMP) and cAMP-dependent protein kinases (PKAs) are believed to be involved in the regulation of essential spermatozoal functions, such as motility, epididymal maturation, capacitation, and the acrosome reaction. In this study, we document the presence of significant mRNA levels for 5 different PKA subunits (RI α, RI β, RII α, RII β, and C α) in germ cells and demonstrate differential expression patterns for these subunits during spermatogenesis. Messenger RNAs for RI (RI α and RI β) and C α appear to be induced at premeiotic germ cell stages, whereas mRNAs for RII (RII α and RII β) are first expressed at haploid stages. The individual PKA subunits may convey specific functions in developing germ cells and mature sperm. The present study, furthermore, demonstrates the presence of unique smaller-sized mRNAs in germ cells compared with somatic cells. Specific, truncated forms of RI α, RII α, RII β, and C α mRNAs appear to be selected in the germ cells. Our data suggest this to be due to the use of alternative polyadenylation site signals. The selection of shorter mRNA species, with higher stability, may be essential for the delayed translation observed in spermatids. This may ensure certain levels of mRNA for translation at late spermatid stages, after cessation of transcription.