Breed, William GodfreyFlaherty, Sean P.2013-10-082013-10-081986http://hdl.handle.net/2440/80398The primary aim of this study was to examine the structure and function of the three curved hooks on the apical margin of the sperm head of the plains mouser Pseudomys australis. There is a single dorsal hook, and two ventral hooks which are united caudally, and each has a characteristic shape. Electron microscopical studies of late spermatids and spermatozoa revealed that the dorsal hook is structurally similar to the falciform sperm head of the rat. The core of the ventral hooks consists of sub-acrosomal material, and bundles of microfilaments which appear to have a morphogenetic role in shaping the hooks. The peripheral layer is an extension of the post-acrosomal dense lamina, with rows of parallel ridges linking the plasma membrane and lamina. The structure of the sperm head posterior to the hooks follows the general mammalian pattern. Electrophoretic analysis of sperm head proteins revealed that the major constituent of the sub-acrosomal material in the hooks is one or more 15 kd polypeptides. A 42 kd protein which comigrates with actin is also present, thus confirming the localization of actin filaments in the ventral hooks using NBD-phallacidin. Epididymal maturation involves a remodelling of the apical segment of the acrosome, migration of the cytoplasmic droplet, acquisition of motility and stabilization of sperm head and tail structures, including the ventral hooks, by disulphide bonds. Oocyte-cumulus complexes were studied at the EM level after routine fixation, or staining with ruthenium red but no unusual structural features were noted in either the cumulus oophorus or zona pellucida. Attempts to study gamete interactions in vitro were hampered by initial difficulties in superovulating female plains mice. Hence, a heterologous I.V.F. system was used with plains mouse sperm and zonafree rat, and laboratory mouse oocytes, but only low rates of fertilization were obtained. The functional design of the sperm head is discussed in relation to a possible role for the hooks in assisting penetration of the oocyte investments. The possibility that, the ventral hooks arose as a reproductive isolation mechanism is also discussed.dorsal hook; rat; mouse; sperm head; pseudomys australisThesis20131003142234