Impaired transcription of human endogenous retroviruses in the sperm with exception of syncytin 1: short communication.

Human endogenous retroviruses (HERVs), remnants of ancestral infections, represent 8% of the human genome. HERVs are co-opted for important physiological functions during embryogenesis; however, little is known about their expression in human gametes. We evaluated the transcriptional levels of several retroviral sequences in human spermatozoa. We assessed, through a Real-Time PCR assay, the transcription levels of the pol genes of HERV-H, -K and -W families and of env genes of syncytin (Syn)1 and Syn2 in the spermatozoa from 8 normospermic subjects. The entity and distribution of their expressions were compared to values found in white blood cells (WBCs) from 16 healthy volunteers. The level of HERV transcripts was significantly lower in spermatozoa than in WBCs for HERV-H-pol, HERV-K-pol, HERV-W-pol, and Syn2.In contrast, the level of expression of Syn1 in the sperm was similar to that found in WBCs and it was significantly higher than the mRNA concentrations of other HERV genes in spermatozoa. Our findings show, for the first time, the presence of several retroviral mRNAs in the sperm, although in low amounts. The higher concentration of Syn1 suggests that it could play a key role in the fusion process between gametes during fertilization and, perhaps, be involved in embryo development. Further studies could clarify whether aberrant HERV expressions, in particular of Syn1, negatively affect fertilization and embryo growth and whether sperm manipulation procedures, such as cryopreservation, may potentially influence HERV transcription in the human male gamete.