Capacitation and the acrosome reaction in marsupial spermatozoa

Although yet to be established definitively, it appears that marsupial spermatozoa require a process of capacitation and that the mechanisms involved may be quite different between the Australian and American species. For Australian species, failure to induce this functional event in culture has meant that in vitro fertilization (IVF) is yet to be achieved. However, in the American species with paired spermatozoa, IVF and subsequent embryo development have been obtained under quite simple culture conditions. Our understanding of the interactions of marsupial spermatozoa with the female tract, and in particular the oviduct, the most likely site of capacitation, is discussed. Although the acrosome reaction (AR) is an equally critical event in marsupial fertilization it appears to be regulated quite differently. The uniquely stable character of the marsupial acrosome is examined as well as our current understanding of the regulation of the marsupial sperm AR in vivo and in vitro.