Spermatozoal RNA as reservoir, marker and carrier of epigenetic information: implications for cloning.

The mammalian male gamete is transcriptionally silent as a consequence of the highly condensed architecture of its chromatin and there is also little or no cytoplasm capable of supporting translation; however, we now understand that under certain conditions, spermatozoa can translate their mRNAs de novo and that spermatozoal RNA can potentially affect phenotypic traits in offspring. This epigenetic phenomenon may involve the transmission of extra-chromosomal episomal elements. Recent evidence indicates that spermatozoal RNA may play a role in the progressive shutdown of transcription during spermiogenesis. The presence of RNA in the sperm nucleus and its potential as a carrier of epigenetic information to the egg may prove insightful with regard to the abysmal success rates for cloning of domestic species by somatic nuclear transfer procedures.