In vitro maturation of oocytes from a marsupial, the tammar wallaby (Macropus eugenii)

Emerging arguments for reproductive technologies in wildlife and their implications for assisted reproduction and conservation of threatened marsupials

Assisted reproductive technologies (ARTs) have significant potential to make a meaningful contribution to the conservation of threatened wildlife. This is true of Australia's iconic, and endangered koala (Phascolarctos cinereus). If developed, ARTs could offer a solution to manage genetic diversity and costs in breeding programs and may provide frozen repositories for either insurance or the practical production of genetically resilient koalas for release and on-ground recovery. Holding back the wider use of ARTs for koalas and other wildlife is a lack of funding to close the remaining knowledge gaps in the marsupial reproductive sciences and develop the reproductive tools needed. This lack of funding is arguably driven by a poor understanding of the potential contribution ARTs could make to threatened species management. We present a review of our cross-disciplinary and accessible strategy to draw much needed public attention and funding for the development of ARTs in wildlife, using emerging cost and genetic modelling arguments and the koala as a case study.

Marsupials the alternative therians - From gametes to birth

Marsupial reproduction shares many common features with the more familiar eutherian mammals but things are often done differently, in alternative ways. Like the eutherians marsupials are placental but the period and degree of development supported in the uterus is much shorter and the long growth phase of development is supported by lactation. But these different ways of achieving often similar outcomes are also seen in gamete formation and function, fertilization and early development. This review presents an overview of marsupial reproductive biology with an emphasis on gamete biology.

Marsupials: Progress and Prospects

The chapter provides a review of the application of reproductive science to technologies for marsupial conservation and population management and discusses prospects for the future. This includes the status of technologies such as sperm freezing, artificial insemination, and exogenous hormone treatments to stimulate ovarian activity and cycling in the female. Fertility-based population management for introduced pest species and over-abundant native marsupials remain an elusive goal. Immune-contraceptive approaches, despite demonstration of basic effectiveness, have not progressed to field deliverable agents. Emerging genetic technologies such as gene drives offer great promise, but gene modifications face major challenges to be broadly accepted both socially and politically. A main theme is the potential advantages, both genetic and economic, of integrating frozen stored genomic material, such as sperm, into the captive breeding component of threatened species strategies. However, the sperm of many marsupial species display no or very poor recovery of motility on thawing. For this reason, it is proposed that the traditional assisted breeding paradigm for conservation-cervical artificial insemination with thawed frozen sperm, based on cattle breeding-is not a viable default strategy. Rather, techniques such as sperm injection and emerging stem cell technologies that utilize stored frozen cells, and in the case of sperm, immotile cells, are better candidates for the development of a more generic approach. In addition, this change in focus encourages wide scale proactive genome storage when genetic diversity is greatest, without the need to demonstrate success in traditional sperm cryopreservation and thawing. However, the promise of the potential of reproductive science to conservation and non-lethal population management is problematic without far greater recognition of, and investment in, the needs of wildlife by society.

Recent advances in tools and technologies for monitoring and controlling ovarian activity in marsupials

Components of assisted reproduction technologies (ART), such as sperm cryopreservation, artificial insemination, superovulation and pouch young surrogacy, have been developed for a range of Australian and American marsupials. However, methods to effectively control ovarian function, arguably the key limiting factors in applying and integrating ART as a practical tool in conservation management, remain poorly developed. This is largely due to unique characteristics of the marsupial corpus luteum and its failure to respond to agents used to synchronize ovarian function in eutherian mammals. This paper presents an overview of relevant aspects of marsupial reproductive biology across marsupial taxonomic groups including information on the long-established technique of removal of suckling young to activate ovarian cycles. Ovarian monitoring tools for marsupials are reviewed and their usefulness for ART assessed (laparotomy, hormone cycling, vaginal cytology, laparoscopy and ultrasonography). We also discuss promising recent work examining the potential of manipulating hypothalamic-pituitary function using GnRH agonists and antagonists as the basis of ovarian control (female synchronization) strategies.

Comparison of the production, quality, and in vitro maturation capacity of oocytes from untreated cycling and intermediate phase equine serum gonadotropin-treated fat-tailed dunnarts (Sminthopsis crassicaudata)

This study describes ovarian changes during the natural and stimulated reproductive cycle of breeding (≤12 month) and retired (>12 month) fat-tailed dunnarts, Sminthopsis crassicaudata. Increased urinary cornified epithelial cells and the influx of leukocytes defined day 0, at which time the naturally cycling females had already ovulated; at day 16 females had no antral follicles, but by day 20 antral follicles had begun to develop. There was no difference between naturally cycling breeding and retired females. Females were stimulated with 1 IU equine serum gonadotropin (eSG) during the intermediate phase on day 16 and killed 3, 4, or 5 days later. Stimulation resulted in a significant increase in the number of growing antral follicles but retired females demonstrated a reduced response. Upon collection from breeding females 4 days following eSG stimulation, 100% of oocytes were at the first polar body (PB1) stage, those collected from retired females were immature upon collection but within 48 h 98.2±1.9% were cultured to the PB1 stage. The rate of ovulation was high in breeding females 5 days following stimulation but retired females were less reliable, and in both groups all oocytes were degraded. This is the first study to describe a reliable technique, involving ovarian stimulation during the intermediate phase and segregation of age groups, allowing the collection of a large number of healthy PB1 stage oocytes from S. crassicaudata. This is important for the development of further assisted reproductive techniques for this species and threatened dasyurids.

In vitro maturation and intracytoplasmic sperm injection of oocytes collected from hormonally stimulated common wombats, Vombatus ursinus

Porcine FSH/LH stimulation successfully induced development of multiple large (>or=4mm) antral follicles in 10 of 11 common wombats. A mean of 5.5 metaphase II (MII) oocytes were aspirated from wombats that were stimulated during the follicular phase of the oestrous cycle (n=3) or after pouch young removal (n=3). Three subadults (n=3) and two anoestrus adults did not produce MII oocytes despite pFSH/pLH administration. In vitro maturation of immature oocytes at the time of aspiration doubled the number of MII oocytes that could be collected from pFSH/pLH stimulated wombats. Immature oocytes with cumulus attached, matured more readily to the MII stage than immature oocytes without cumulus. Following intracytoplasmic sperm injection (ICSI), approximately 5% of the oocytes that were MII at the time of collection cleaved. Approximately 5% of those that were matured by in vitro maturation (IVM) formed two polar bodies following ICSI, although they not cleave. Parthenogenesis cannot be excluded. This demonstrates that assisted reproductive technologies may be applicable to the common wombat.

Growth and histology of ovarian follicles after cold storage in the tammar wallaby

Cold storage is a simple method for storing and transporting tissues and organs. The reliability of this method for maintaining structure and function of marsupial ovarian tissue was assessed using histological techniques and follicle culture. Tammar wallaby ovaries were placed in cold storage (phosphate-buffered saline at 4°C) for 24 or 48 h. Although necrotic changes were evident in the germinal epithelium, cortex and interstitial tissue after cold storage, there was little evidence of necrotic changes in ovarian follicles and oocytes appeared normal. Secondary follicles isolated from ovarian tissue after cold storage grew by a similar amount to non-stored follicles when cultured for 4 days in vitro, but no follicles from any group developed to tertiary follicles. Cold storage for up to 24 h had little obvious effect on the structure of ovarian tissue and follicles isolated from this tissue maintained their structure during culture. However, degeneration in culture increased with storage time and was significantly higher after cold storage for 48 h. As demonstrated in the tammar wallaby, cold storage has potential as a method for storage and transport of marsupial ovaries up to 24 h.

In vitro and in vivo maturation of oocytes from gonadotrophin-treated brushtail possums

The time course of nuclear maturation of oocytes was examined in brushtail possums, Trichosurus vulpecula. Oocytes were recovered from ovarian follicles > 2 mm in diameter after pregnant mares' serum gonadotrophin/porcine luteinizing hormone (PMSG/LH) treatment (in vivo matured) or 72 hr after PMSG treatment (in vitro matured). Oocytes recovered from small (< 2 mm) and large (> 2 mm) follicles were also assessed for their ability to mature in vitro. Staining with the DNA-specific dye Hoechst 33342 was used to assess the stage of nuclear development by fluorescence microscopy. The process of nuclear maturation progressed rapidly in vivo, as oocytes collected at 20-27 hr post-LH all had a GV, but by 28-29.5 hr post-LH approximately a third of eggs were MII. By 30-hr post-LH, more than 70% of oocytes had reached MII stage and all ovulated eggs were MII. In vitro, all oocytes were at germinal vesicle stage at the start of culture. After 24 hr of culture, 67% of oocytes had progressed to metaphase I/anaphase I of meiosis. After 36 hr, 25% of oocytes had completed maturation to metaphase II, increasing to 52% after 48 hr. Maturation of oocytes after 48 hr in culture was unaffected by the presence or absence of granulosa cells, PMSG or LH/porcine follicle stimulating hormone (FSH). More oocytes from large follicles (55%) completed maturation by 48 hr than from small follicles (15%). The potential of oocytes to mature after 48 hr in culture was dependent on the follicle harvested having reaching a critical diameter of 1.5 mm.

Follicular development in cryopreserved Common Wombat ovarian tissue xenografted to Nude rats

The Northern Hairy-nosed Wombat (Lasiorhinus krefftii) is a highly endangered marsupial species and every possible option for sustaining the species needs to be explored. One important approach may be the development of assisted reproductive technologies in the non-endangered Common Wombat (Vombatus ursinus) and Southern Hairy-nosed Wombat (Lasiorhinus latifrons) for application in breeding the Northern Hairy-nosed Wombat. In this study, it was examined whether cryopreserved Wombat ovarian tissue would develop following xenografting to immunologically deficient rats. Ovarian tissue was collected from Common Wombats (n = 3) and cryopreserved as small cortical pieces. After thawing the cortical pieces were grafted underneath the kidney capsule of Nude rats (n = 16). The grafts were recovered at 2, 4, and 10 weeks after transplantation and their gross and histological appearance investigated. Two weeks after grafting (n = 2), the tissue was revascularized and healthy primordial follicles were present. At week 4 (n = 2), some follicular development was present. At week 10, six rats received human chorionic gonadotrophin (hCG) to trigger follicle and oocyte maturation while another six rats were not given any treatment. The administration of hCG did not induce preovulatory follicles and oocyte maturation although type 5 follicles were present in ovarian tissue collected 10 weeks posttransplantation in both treated and untreated groups. This study demonstrates for the first time that Wombat ovarian tissue can survive and function when grafted into immunocompromized rats and that Wombat ovarian follicles can be recruited to growth and development in an ovarian xenograft. This model system has the potential to produce mature oocytes from endangered species for use in assisted reproductive technologies such as in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI), and mature oocytes from non-endangered species for nuclear transfer which may be necessary for the preservation of critically endangered species.

Further observations of the ovarian response of the tammar wallaby (Macropus eugenii) to exogenous gonadotrophins: an improved method for superovulation using FSH/LH

This study reports the development of an improved superovulation protocol in the monovulatory tammar wallaby, Macropus eugenii. Treatment with pregnant mare's serum gonadotrophin (PMSG; 10-20 IU) inhibited follicle development in the corpus luteum (CL)-bearing ovary and only 2-3 eggs per female could be recovered after ovulation induction with gonadotrophin releasing hormone (GnRH; 3 x 30 microg at 3-h intervals) or porcine luteinizing hormone (LH; 4, 5 or 8 mg) 3 days after PMSG priming. Treatment with porcine FSH (8 x 6 mg at 12-h intervals for four consecutive days) was found to override this inhibition and resulted in the recovery of 7-13 eggs per female after ovulation induction with porcine LH (4 mg on day 5). For these animals, there was no difference in numbers of developing follicles, ovulation sites and eggs recovered between the CL- and non-CL-bearing ovaries. This FSH/LH protocol was effective in both cycling and non-cycling females, and multiple ovulation occurred from about 36 h after LH treatment. After LH treatment, eggs were recovered from the oviduct at 36-50 h. At 51-57 h, 12-25% of eggs were recovered from the uterus, and by 75 h all eggs were recovered from the uterus. It is concluded that the described FSH/LH protocol used results in higher ovulation success than the PMSG/GnRH method.