| | Present Projects 2009/2010Most of our research involves studies on sperm and egg production and structural organisation, their maturation and sperm-egg interaction at fertilisation in Australian mammals. Present projects include:- POTENTIAL HONOURS PROJECTS 1 Do the molecules involved in sperm-egg interaction at fertilisation undergo rapid evolution?
Most of the native Old Endemic Australian rodents have highly complex spermatozoa that have a more elaborate sperm head cytoskeleton than that of all other eutherian mammals. Nevertheless in three lineages there are a few species where highly morphologically divergent sperm have evolved. We have recently carried out a study on the molecular evolution of the sperm binding region on the egg coat protein, zona pellucida 3, of these species (see Swann et al REPRODUCTION, 2007, volume 133, pages 697-708). We now propose to extend this study by (1) investigating the evolution of the egg coat protein, zona pellucida 2, that is involved in secondary sperm binding, and (2) determining whether complementary evolution of the molecules on the sperm surface, and in particular that of acrosin, has occurred, in this group of mammals (with Steve Cooper, South Australian Museum). 2 Do marsupial eggs exhibit polarity and, if so, does this determine the site of sperm-egg binding and entry?
The eggs (=oocytes) of placental mammals appear to have randomly distributed organelles within the cytoplasm with the site of sperm binding and fusion being randomly located except for the cell membrane overlying the meiotic spindle to which sperm binding and fusion cannot occur. By contrast eggs (=oocytes) of other vertebrates are polarised and with a localised site for sperm binding and penetration. What about the eggs (=oocytes) of marsupials? There is at present contradictory evidence for cytoplasmic polarity and whether localisation of the site for sperm binding and penetration occurs. We have obtained many mature eggs from a diverse array of marsupial species and we plan to use this material to determine whether polarity is present in the oocyte cytoplasm and whether this relates to the site of sperm binding, fusion and entry. 3 What is the significance of variation of ovarian interstitial tissue organisation in marsupials and native rodents?
Previous studies carried out in our laboratory have shown that in both native Australian rodents and marsupials there are marked differences in the extent and cellular organisation of the ovarian interstitial tissue. The reasons for this are not apparent at the present time but they may relate to variation in steroid hormone synthesis perhaps due to differences in endocrine control of ovulation. This hypothesis will be tested by determining the abundance and distribution of steroid hormone enzymes within the ovary of selected marsupial and rodent species (with Dr. Dave Taggart, Adelaide Zoo Research Officer ). 4 What are the cellular and morphological differences that occur in the gastrointestinal tract of the Old Endemic native rodents that eat different diets?
The Old Endemic rodents of Australia have a variety of different diets ranging from omnivory, carnivory, herbivory to frugivory. We have found that, coevolving with these differences in diets, there are major interspecies differences in the relative size and proportions of the stomach, small and large intestines and caecum (see Breed and Ford, 2007, Native mice and rats published by CSIRO publishing company). We now intend to use this material to investigate the interspecies differences in cellular morphology of the different regions of the GI tract (with Dr Rachel Gibson). 5 Why are the testes of the hopping mouse so tiny?
Comparative studies of testis size across species of native Australian rodents have shown that the Spinifex hopping mouse has remarkably small testes that are an order of magnitude smaller than those of most rodent species of similar body mass (see Bauer and Breed 2008 Journal of Zoology 274: 349-356) as well as having highly variable spermatozoa (Bauer and Breed 2006 Reproduction Fertility and Development 18: 797-605). These reproductive traits suggest that hopping mice either lack of genetic heterozygosity, and/or exhibit a monogamous mating system with resultant low levels of intermale sperm competition. Using tissue samples that we have recently obtained from a wild population of hopping mice near Roxby Downs in northern South Australia we wish to use microsatellite markers to genotype the individuals so that the population structure and incidence of multiple paternity can be determined. This project may also enable the student to collect further material from the area of Roxby Downs (with Dr. Steve Cooper). 6 Does the zona pellucida of the Old Endemic Australian rodents have 3 or 4 glycoproteins?
The laboratory mouse extracellular glycoprotein coat that surrounds the egg or oocyte, the zona pellucida, is composed of filaments of alternating units of ZP2 and ZP3 which are bound together into a 3D matrix by dimers of ZP1. This model of the zona matrix molecular structure has been extensively used to investigate zona structural organisation and function in mammals including humans, However it has recently become apparent the human zona includes a forth zona glycoprotein, ZP4, with the consequence that the model based on studies of the laboratory mouse may not be applicable for extrapolating to human zona. Surprisingly however it has recently become apparent that, unlike the laboratory mouse, the laboratory rat also expresses ZP4. The question thus arises is how widespread is the expression of ZP4 across murine rodent species. We have recently extracted DNA from a variety of native rodents and we now intend to use this DNA to determine whether ZP 4 is present in these lineages. The results of this study will give insight into the evolution of the zona pellucida glycoproteins in rodents and may also indicate whether the house mouse or lab rat is closer phylogenetically to the Old Endemic rodents of Australia (with Steve Cooper and Chris Swann). Contacts for the above projects: Associate Professor William Breed
Tel. - 8303 5743.
email - william.breed@adelaide.edu.au,
Dr Rachel Gibson
Tel - 8303 1023
email - rachel.gibson@adelaide.edu.au
Dr Eleanor Peirce
Tel. - 8303 5191;
email: eleanor.peirce@adelaide.edu.au,
Mario Ricci (Tel. - 8303 6294,
email: mario.ricci@adelaide.edu.au Research Papers 2001-2002
2003-2006
2007-2009 Research Links Structural organisation of the sperm and eggs
Molecular and cellular aspects of sperm-egg interactions during fertilisation
Dynamics of production of male germ cells and testis function | |
