Non-traditional roles of ubiquitin-proteasome system in fertilization and gametogenesis.

Fertilization and gametogenesis are key events in sexual reproduction. Our recent studies, together with several reports by other authors, demonstrated that the extracellular ubiquitin-proteasome system plays a role in fertilization and gametogenesis in addition to the traditional intracellular ubiquitin-proteasome system. Here, we summarize our recent results showing the importance of the extracellular ubiquitin-proteasome system in the sperm penetration through the vitelline coat of the egg during ascidian fertilization, together with our recent reports implicating the participation of a novel proteasome-associating complex PC530 in starfish oocyte maturation. We also describe the results by other authors showing the participation of the ubiquitin system both in the elimination of defective sperm in epididymis and in the elimination of paternal mitochondria in fertilized eggs. These are evidence of non-traditional extracellular functions of the ubiquitin system.