Mammalian Spermatozoal Biology

Sperm Function

Epididymal Transit and Maturation

Upon leaving the testis, spermatozoa are incapable of progressive movement or the cascade of cellular events that result in fertilization of the oocyte. These functional characteristics are only acquired as spermatozoa undergo maturation during epididymal transit. Given the absolute importance of epididymal maturation for the generation of fertile spermatozoa, it is clearly important that the molecular mechanisms supporting this functional transformation be elucidated. Success in this area will have implications both for development of reversible male contraceptive agents and the aetiology of male infertility. This project aims to characterise changes in tyrosine phosphorylation and mitochondrial activation which appear to be particularly important parts of epididymal maturation.

Supervisor: Professor John Aitken

Capacitation and Development of Fertilizing Ability

Transcriptionally inactive spermatozoa rely totally on Post-translational modifications in order to acquire functional competence. These processes occur in two distinct phases; firstly, spermatozoa pass through the epididymal luman, and secondly, inside the female reproductive tract as sperm capacitate. Both events are essential for fertility, however, the biochemical mechanisms behind the maturation of these cells is unclear. This project aims to characterise the entire gamete of proteins present in spermatozoa. It will also decipher which proteins (peptides) are up/down regulated, or completely new/lost during both maturation procedures. changes in tyrosine phosphorylation and mitochondrial activation which appear to be particularly important parts of epididymal maturation.

Supervisor: Professor John Aitken

Mitochondrial Function and Reactive Oxygen Species

Reactive oxygen species (ROS) are conventionally considered as detrimental by-products of cellular metabolism, which generate a state of oxidative stress in susceptible cells. Despite the pathophysiological significance of ROS generation in the male germ line, neither the sub-cellular origin nor the biochemical basis for this activity has been established. The major source of ROS generation in somatic cells is postulated to involve electron leakage from the mitochondrial electron transport chain during cellular respiration. In view of our poor understanding of mitochondrial function in spermatozoa, and the potential importance of these organelles as a potential source of oxidative stress in the male germ line in particular, this project is an analysis of the potential competence of human sperm mitochondria to generate ROS and to characterise the significance of this activity in the aetiology of defective sperm function.

Supervisor: Professor John Aitken

Monotreme sperm biology

As iconic symbols of Australia's unique fauna the platypus and echidna generate considerable interest from tourists and the Australian public, thus ensuring that their display in zoos is of significant commercial value. Nevertheless, the record of breeding the 3 extant monotremes in captivity is poor, and the New Guinea echidna faces extinction in the wild. Consequently, knowledge of monotreme reproductive biology is important for conservation practices. This project focuses on elucidation of the molecular processes leading to fertilization in monotremes, including: the proteins which form sperm into bundles to greatly enhance their motility (a unique sperm competition strategy) and the mechanisms involved in sperm bundle formation. The work will provide an understanding of the biological significance of adaptations unique to mammals, the need for maturation of sperm in the epididymis and a subsequent period of capacitation before they are capable of fertilizing an ovum.

Supervisors: Dr Brett Nixon and Adjunct Associate Professor Russell Jones