Accumulation of transcripts in the mature human sperm nucleus: implication of the haploid genome in a functional role

The existence of sperm-specific transcripts has been suggested by a number of studies performed both in man and rodents but their origin and role are not yet elucidated. For evaluating the functional significance of these mRNAs, transcripts coding for proteins expressed during spermiogenesis or potentially implicated in the early steps of zygote development, have been searched in human testis and sperm cells by RT-PCR. Furthermore their localization in spermatozoa has been checked by in situ hybridization. Our results confirm the presence of basic nucleoproteins (Transition proteins 1 and 2, Protamines 1 and 2) spermatozoal transcripts which probably represent remnants of previous transcription. They also reveal the existence of sperm specific mRNAs coding for the transcription factor Stat 4, the cyclin B1 and for the testicular isozyme of the angiotensin converting enzyme ACE. On the contrary, mRNAs coding for the heat shock protein Hsp 70 have been found in testis but not in spermatozoa. The possible roles of these transcripts either during the fertilization process or in zygote are discussed.