Haploid transcripts persist in mature human spermatozoa

Mammalian spermiogenesis is marked by the morphological and functional differentiation of round haploid spermatids into mature spermatozoa. A molecular restructuring of the chromatin accompanies this process facilitated by the transition proteins and protamines which compact and condense the genetic material within the developing spermatid. Previous studies from this laboratory have demonstrated that human protamines PRM1, PRM2 and transition protein TNP2 transcripts are associated with round and elongating spermatids. Extending this investigation, we examined the occurrence of these transcripts in mature spermatozoa by in-situ hybridization analysis using [³⁵S]-labelled cRNA probes. These results demonstrate that PRM1, PRM2 and TNP2 haploid-specific transcripts are present in mature spermatozoa. Quantitative analysis of the localized signal also indicates that the PRM1, PRM2 and TNP2 transcripts persist at a similar ratio to that previously described for these transcripts in human testes, i.e. PRM2>PRM1≈TNP2. The persistence of these transcripts in mature spermatozoa warrants further investigation.