Sperm are highly specialized cells of the body responsible for carrying the genetic message to the progeny to join the female egg. This should be a highly regulated process to achieve the evolving and maintaining a healthy embryo expression patterns characteristic of our species. Germ cells of man must have a highly specific epigenome to develop this role and very different from the other cells and tissues.

The team led by Manel Esteller, director of the Epigenetics Cancer and Biology Program at the Bellvitge Biomedical Research Institute (IDIBELL), Professor of Genetics at the University of Barcelona and ICREA researcher, has produced the first epigenetic map of human sperm DNA and its alterations in diseases. The research has been elaborated jointly with researchers Sara Larriba, from the group of Molecular Genetics of Male Infertility at the IDIBELL, Lluís Bassas, from the Andrology Service at the Fundació Puigvert, and Csilla Krausz, from the University of Florence and Fundació Puigvert. The finding is published simultaneously this week in two papers in the journal PLOS One.

The research team studied half a million points of DNA methylation, best known epigenetic signal, in sperm from healthy donors. They found differences between epigenetic marks present in the sperm of different individuals which could contribute to the variability of the population, that is, we are all different from each other. “What is more curious is that not all sperm from the same individual is epigenetically identical, which helps to explain why all brothers born of the same parents are not identical to each other”, says Dr. Esteller on the result of the studies.

In addition, the sperm epigenome is radically different from the non-reproductive cells. One of the most striking aspects is that it has activated very small molecules called piRNAs that are essential to silence part of our DNA, the genetic material must be inactive in the reproduction process. “The piRNAs are so important that epigenetic changes in genes that produce them are associated with decreased sperm production in the testis, and therefore the appearance of male infertility, by an insufficient number of sperm in the semen, what is known as oligozoospermia or azoospermia”, argues Dr. Larriba.

These findings therefore “help to clarify the variability present in the next generation (why children are not a sum equal half of genes from the father and half from the mother’s genes), explain some cases of male infertility and provide elements that facilitate investigation of male infertility treatment”, concludes Esteller.

Reference of the papers:

Novel insights into DNA methylation features in spermatozoa: stability and peculiarities. Krausz C, Sandoval J, Sayols S, Chianese C, Giachini C, Heyn H, Esteller M. PLOS One. 2012; 7(10):e44479.

Epigenetic Disruption of the PIWI Pathway in Human Spermatogenic Disorders. Heyn H, Ferreira HJ, Bassas L, Bonache S, Sayols S, Sandoval J, Esteller M, Larriba S. PLOS One. 2012; 7(10):e47892.