Unscrambling the oocyte and the egg: clarifying terminology of the female gamete in mammals

Most reproductive biologists who study female gametes will agree with the 16th century anatomist William Harvey’s doctrine: ‘Ex Ovo Omnia’. This phrase, which literally translates to ‘everything from the egg’, recognizes the centrality of the egg in animal development. Eggs are most impressive cells, capable of supporting development of an entirely new organism following fertilization or parthenogenetic activation. Not so uniformly embraced in the field of reproductive biology is the nomenclature used to refer to the female germ cell. What is an oocyte? What is an egg? Are these terms the same, different, interchangeable? Here we provide functional definitions of the oocyte and egg, and how they can be used in the context of mammalian gamete biology and beyond.

Challenges associated with the development and transfer of assisted breeding technology in marsupials and monotremes: lessons from the koala, wombat and short-beaked echidna

This reflective review describes how a research model, which was originally established for the successful AI of the koala (Phascolarctos cinereus), is currently being developed and extended to the wombat (Lasiorhinus latifrons and Vombatus ursinus) and short-beaked echidna (Tachyglossus aculeatus). The research model centres around the establishment of an AI program and involves: (1) semen collection, evaluation and preservation, requiring an understanding of male reproductive physiology and gamete biology; (2) timing of insemination, based on a knowledge of oestrous cycle and gestation physiology and oestrous behaviour; and (3) the appropriate placement of semen, which relies on an accurate description of female reproductive anatomy. Published and unpublished studies of assisted breeding technology (ABT) development in all three species of Australian mammals reported in this review (koala, wombat and short-beaked echidna) clearly demonstrate the importance of recognising species-specific variation in reproductive biology. Even in closely related species, such as the koala and wombat, subtle differences in reproductive physiology can hinder the transfer of ABT across species. Significant progress in marsupial and monotreme ABT will also require adequate access to captive wildlife colonies (zoos, university collections and private partners) in sufficient numbers in order to conduct quality science.

046. FUTURE PROOFING AUSTRALIA'S MAMMALIAN BIODIVERSITY USING GENOME RESOURCE BANKING AND ART: WHERE ARE WE UP TO?

The establishment of a functional genome resource bank for the genetic management and future proofing of Australian native mammals sounds great in theory, but what is the reality of this idea. In order to understand the current rate of progress in this area, we will present an overview of the inherent structural and physiological limitations of non-eutherian mammalian reproduction in terms of gamete biology and ART. For the male, these include (1) an unique mode of spermatid condensation that imparts the need for major structural changes to sperm morphology during epididymal transit, (2) a lack of cysteine protamines and disulphide bonds in the sperm chromatin that predisposes the nucleus to post-thaw chromatin relaxation, (3) an extremely stable acrosome, which to date, has not been possible to experimentally react in vitro, (4) unusual lipid composition in the plasma membrane that potentially makes the sperm cell resistant to cold shock trauma and (5) the need, in some species, for extremely high concentrations of cryoprotectant, that paradoxically, appear to be cytotoxic to the spermatozoon. Female limitations include, (1) the production of a large yolky oocyte and resulting embryo, making it difficult to cryopreserve, (2) a small and technically challenging complex reproductive tract that makes gamete recovery and artificial insemination problematic and (3) a general lack of information on marsupial reproductive physiology and behaviour that has hindered the development of protocols for timed induction of oestrus and ovulation. We shall also identify, socio-political and ethical limitations holding back the application of assisted breeding technology in these species.

Gamete biology of the new world marsupial, the grey short-tailed opossum, Monodelphis domestica

Mammalian gametes undergo a series of functional and developmental changes that culminate in fertilization. In order to appreciate the necessity for such complex processes as sperm maturation, capacitation and the intimate sperm-egg interactions leading to gamete fusion, it is important to understand how gametes may have evolved. In this respect, marsupials are particularly relevant since they exhibit features reminiscent of both non-mammalian vertebrates and eutherian mammals. The grey short-tailed opossum, Monodelphis domestica, is a New World marsupial from Brazil. It breeds well under laboratory conditions and is an excellent animal model to investigate marsupial gamete biology. As in other American marsupials, the spermatozoa of the opossum form pairs in the epididymis. Here, a number of studies carried out in this laboratory, related to sperm maturation, capacitation and fertilization in M. domestica, are reviewed and the gamete biology in this species is compared with what is known in other marsupials and eutherian mammals.