First expression of protamine message in trout testis

In situ hybridizations were performed using a biotinylated riboprobe complementary to protamine messenger RNA in order to directly examine the various cell types in the trout testis for the presence of protamine message. Computer-aided optical density measurements were used to provide estimates of transcript abundance for cells identified by their DAPI-labeled nuclei. Optically detectable protamine hybridization occurred only in spermatid cells. These findings are in accord with results obtained in other species which report protamine mRNA only in the post-meiotic spermatid cell; but they are in conflict with a previous study employing solution hybridization which noted that protamine message first appears in the spermatocytes of rainbow trout.