RNA in the ejaculate spermatozoon: a window into molecular events in spermatogenesis and a record of the unusual requirements of haploid gene expression and post-meiotic equilibration.

Several reports demonstrating the presence of messenger RNAs for sperm-specific nucleoproteins, the protamines PRM-1, PRM-2, and the transition protein TP-1 as well as beta-actin, c-MYC, HLA1, and beta 1 integrin have challenged the accepted view of the transcriptional dormance of terminally differentiated spermatozoa. Whatever nuclear activity the ejaculate spermatozoon may possess, these data suggest that spermatozoa are a repository of information regarding meiotic and post-meiotic gene expression in the human and are likely to contain transcripts for many homologues of genes identified from animal models, which play an essential role in spermiogenesis. The use of ejaculate spermatozoa as a wholly non-invasive biopsy of the spermatid should now be evaluated. At the same time, spermatozoal RNAs require further analysis and characterization. One explanation for their persistence in ejaculate spermatozoa is that they serve to equilibrate imbalances in spermatozoal phenotypes brought about by melotic recombination and segregation. Transcript exchange is likely considering the presence of inter-cellular cytoplasmic bridges between haploid spermatids, which also offers a route for the translocation and expansion of non-mendelian trials linked to retrotransposon activity.