Ensuring continuity of the paternal genome: potential roles for spermatozoal RNA in mammalian embryogenesis.
The mammalian male gamete is traditionally considered to be a less complex cell than its female counterpart, primarily because all development (bar oocyte activation) is thought to be initiated by the egg. However, the spermatozoon is exquisitely specialised to deliver the paternal genome to the oocyte and, in this respect, is pared down to carry out that job as efficiently as possible. As such, it is transcriptionally silent as a consequence of the highly condensed architecture of its chromatin and yet some spermatozoal DNA may be organised into domains that resemble sites of transcriptional activity. There is also little or no cytoplasm capable of supporting translation; however, we now understand that these cells carry a cargo of translationally competent mRNAs. Moreover, a recent report has provided intriguing new evidence that, under certain conditions, spermatozoa can translate their mRNAs de novo. Indeed, delivery of an RNA cargo by the spermatozoon to the oocyte may be as fundamental a feature of this quiescent cell as delivery of the paternal genome itself. New evidence is available showing that spermatozoal RNA can potentially affect phenotypic traits in offspring. This epigenetic phenomenon may involve the transmission of extrachromosomal episomal elements. Taken together, these data suggest that the spermatozoon is much more than the sum of its constituent parts and that the continued transmission of male-benefit genes and possibly selfish elements may be one reason for the male gamete's additional and unexpected investment in delivering the paternal genome safely and efficiently.
Miller
David
D
Reproduction and Early Development Group, University Department of Obstetrics and Gynaecology, Level D, Clarendon Wing, Leeds General Infirmary, Belmont Grove, Leeds, LI2 9NS, UK. d.miller@leeds.ac.uk
D000818:Animals; D047108:Embryonic Development / Q000502:physiology; D044127:Epigenesis, Genetic; D005260:Female; D016678:Genome; D006801:Humans; D008297:Male; D008322:Mammals / Q000502:physiology*; D010334:Paternity; D010641:Phenotype; D012313:RNA / Q000502:physiology; D013094:Spermatozoa / Q000502:physiology
D012313:RNA