Protamine messenger RNA: Evidence for early synthesis and accumulation during spermatogenesis in rainbow trout

Abstract

Trout testis cells were separated into various developmental classes by velocity sedimentation in bovine serum albumin gradients and were identified morphologically with particular stages of the process of spermatogenesis. The stage of testis cell differentiation at which protamine mRNA appears in the cell cytoplasm for the first time was determined by hybridization of RNA populations extracted from the separated cells to radioactively labeled protamine cDNA. Primary spermatocytes represent the earliest stage of differentiation at which protamine mRNA can be detected in large quantities in the cell cytoplasm, establishing that the synthesis of this class of mRNA occurs at a much earlier stage than the time of its translation at the spermatid stage. Protamine mRNA sequences were found in both the polysomes and postribosomal supernatant of the spermatid cells which are involved in the synthesis of protamine, while primary and secondary spermatocytes contained the mRNA sequences only in their postribosomal supernatant fractions. These findings strongly suggest that protamine mRNA is synthesized, accumulated, and stored in the cell sap of primary and secondary spermatocytes in the form of “inactive” messenger ribonucleoprotein particles, which are “activated” and translated at the spermatid stage.