Role of glycosaminoglycans in sperm chromatin decondensation in humans

In the sperm nucleus, chromatin is 6 to 8 times more condensed than in the nuclei of somatic cells. This high condensation is the result of the exchange between histones and protamines during the process of spermatogenesis, and provides the genetic material with unique resistance to the attack of reactive oxygen species, as well as to the stress of the voyage towards the encounter with the oocyte in the oviduct. This high condensation must be relaxed, once the fertilization of the oocyte has taken place, in order to allow for the formation of male pronucleus and subsequent syngamy. For the decondensation to occur, it is necessary to reduce the disulfide bonds in the protamines, reaction that takes place with the assistance of glutathione, and also to remove the protamines with the subsequent or concomitant exchange with oocyte histones. At this point, there is no consensus regarding the molecule involved in this process. In these studies, it has been postulated that this molecule is heparan sulfate, based on in vitro decondensation studies, on the structural characteristics of the molecule and the fact that it is present in the murine oocyte, with preliminary evidence of its presence also in the human oocyte (data not shown).