Hormonal and Molecular Regulation of Phallus Differentiation in a Marsupial Tammar Wallaby

Congenital anomalies in phalluses caused by endocrine disruptors have gained a great deal of attention due to its annual increasing rate in males. However, the endocrine-driven molecular regulatory mechanism of abnormal phallus development is complex and remains largely unknown. Here, we review the direct effect of androgen and oestrogen on molecular regulation in phalluses using the marsupial tammar wallaby, whose phallus differentiation occurs after birth. We summarize and discuss the molecular mechanisms underlying phallus differentiation mediated by sonic hedgehog (SHH) at day 50 pp and phallus elongation mediated by insulin-like growth factor 1 (IGF1) and insulin-like growth factor binding protein 3 (IGFBP3), as well as multiple phallus-regulating genes expressed after day 50 pp. We also identify hormone-responsive long non-coding RNAs (lncRNAs) that are co-expressed with their neighboring coding genes. We show that the activation of SHH and IGF1, mediated by balanced androgen receptor (AR) and estrogen receptor 1 (ESR1) signalling, initiates a complex regulatory network in males to constrain the timing of phallus differentiation and to activate the downstream genes that maintain urethral closure and phallus elongation at later stages.

Marsupial tammar wallaby delivers milk bioactives to altricial pouch young to support lung development

Our research is exploiting the marsupial as a model to understand the signals required for lung development. Marsupials have a unique reproductive strategy, the mother gives birth to altricial neonate with an immature lung and the changes in milk composition during lactation in marsupials appears to provide bioactives that can regulate diverse aspects of lung development, including branching morphogenesis, cell proliferation and cell differentiation. These effects are seen with milk collected between 25 and 100days postpartum. To better understand the temporal effects of milk composition on postnatal lung development we used a cross-fostering technique to restrict the tammar pouch young to milk composition not extending beyond day 25 for 45days of its early postnatal life. These particular time points were selected as our previous study showed that milk protein collected prior to ~day 25 had no developmental effect on mouse embryonic lungs in culture. The comparative analysis of the foster group and control young at day 45 postpartum demonstrated that foster pouch young had significantly reduced lung size. The lungs in fostered young were comprised of large intermediate tissue, had a reduced size of airway lumen and a higher percentage of parenchymal tissue. In addition, expression of marker genes for lung development (BMP4, WNT11, AQP-4, HOPX and SPB) were significantly reduced in lungs from fostered young. Further, to identify the potential bioactive expressed by mammary gland that may have developmental effect on pouch young lungs, we performed proteomics analysis on tammar milk through mass-spectrometry and listed the potential bioactives (PDGF, IGFBP5, IGFBPL1 and EGFL6) secreted in milk that may be involved in regulating pouch young lung development. The data suggest that postnatal lung development in the tammar young is most likely regulated by maternal signalling factors supplied through milk.

Effects of nutritional manipulation on body composition in the developing marsupial, Macropus eugenii

When 60-day-old tammar wallaby pouch young (Macropus eugenii) are fostered to mothers at 120 days of lactation, their growth, developmental rate and maturation of their GH/IGF axes are markedly accelerated. To determine the effect of fostering on energy intake, body composition and fat accretion, we first measured total body fat and lean mass in these young. Next, we mimicked the triglyceride oleic and palmitic acid composition of 120-day milk by supplementing 60 day young with these fatty acids and comparing their growth with that of growth accelerated young. There was no difference in the weight or growth axis maturation of supplemented young but there was significantly more body fat in these and in the growth-accelerated fostered young than in controls. We conclude that the accelerated growth and GH/IGF axis maturation observed previously in fostered young is most likely due to increased milk consumption and earlier access to specific nutrients.

Anthelmintic Treatment Does Not Change Foraging Strategies of Female Eastern Grey Kangaroos, Macropus giganteus

Large mammalian herbivores are commonly infected with gastrointestinal helminths. Heavily parasitised hosts are likely to have increased nutritional requirements and would be predicted to increase their food intake to compensate for costs of being parasitised, but experimental tests of the impacts of these parasites on the foraging efficiency of hosts are lacking, particularly in free-ranging wildlife. We conducted a field experiment on a population of free-ranging eastern grey kangaroos (Macropus giganteus) to test this prediction, removing nematodes from one group of adult females using an anthelmintic treatment. We then carried out observations before and following treatment to assess the influence of parasites on foraging behaviour. Contrary to our predictions, the manipulation of parasite burdens did not result in changes in any of the key foraging variables we measured. Our results suggest that despite carrying large burdens of gastrointestinal parasites, the foraging strategy of female kangaroos is likely be driven by factors unrelated to parasitism, and that kangaroos in high nutritional environments may be able acquire sufficient nutrients to offset the costs of parasitism. We conclude that the drivers of forage intake likely differ between domesticated and free-ranging herbivores, and that free-ranging hosts are likely more resilient to parasitism.

Growth axis maturation is linked to nutrition, growth and developmental rate

Maturation of the mammalian growth axis is thought to be linked to the transition from fetal to post-natal life at birth. However, in an altricial marsupial, the tammar wallaby (Macropus eugenii), this process occurs many months after birth but at a time when the young is at a similar developmental stage to that of neonatal eutherian mammals. Here we manipulate growth rates and demonstrate in slow, normal and fast growing tammar young that nutrition and growth rate affect the time of maturation of the growth axis. Maturation of GH/IGF-I axis components occurred earlier in fast growing young, which had significantly increased hepatic GHR, IGF1 and IGFALS expression, plasma IGF-I concentrations, and significantly decreased plasma GH concentrations compared to age-matched normal young. These data support the hypothesis that the time of maturation of the growth axis depends on the growth rate and maturity of the young, which can be accelerated by changing their nutritional status.

Immunohistochemical localization of T-lymphocyte subsets in the developing lymphoid tissues of the tammar wallaby (Macropus eugenii)

Research into marsupial adaptive immunity during ontogeny has been hampered by the lack of antibodies that react to marsupial immunological cell populations. In this study, newly synthesised polyclonal antibodies to the T cell marker, CD8, have been developed and used to investigate the ontogeny and distribution of this T cell population in the tammar wallaby. Immunohistochemical analysis indicated that the distribution of the CD8 lymphocytes in the lymphoid tissues of tammar neonates during the first 144 days of pouch life was similar to that of the eutherian mammals. However, CD8α(+) lymphocytes were observed in the intestines of tammar neonates prior to their first appearance in the cervical thymus, an observation that has not been found in eutherians. A dual labelling immunohistochemical approach was used for the indirect demonstration of CD4 and enabled the simultaneous detection in the tammar wallaby tissues of the two major T-lymphocyte populations, CD4 and CD8 that are associated with adaptive immunity. As in eutherian mammals, CD4(+) cells were the predominant T cell lymphocyte subset observed in the spleen while in the nodal tissues, an age-related decrease in the CD4(+)/CD8(+) ratio was noted. These antibodies provide a new immunological tool to study the role of T cell subsets in marsupial immunity and disease pathogenesis studies.

Maturation of the growth axis in marsupials occurs gradually during post-natal life and over an equivalent developmental stage relative to eutherian species

The separation of a nutrition-responsive insulin-like growth factor (IGF) system and a growth hormone (GH) responsive IGF system to control pre- and post-natal growth of developing mammals may originate from the constraints imposed by intra-uterine development. In eutherian species that deliver relatively precocial young, maturation of the GH regulatory system is coincident with the time of birth. We measured the hepatic expression of the four key growth axis genes GH-receptor, IGF-1 and -2, and IGFBBP-3, and plasma protein concentrations of IGF-1 from late fetal life through to adult stages of a marsupial, the tammar wallaby. The data clearly show that maturation of GH-regulated growth in marsupials occurs gradually over the course of post-natal life at an equivalent developmental stage to that of precocial eutherian mammals. This suggests that the timing of GH-regulated growth in marsupials is not related to parturition but instead to the relative developmental stage.

Genome sequence of an Australian kangaroo, Macropus eugenii, provides insight into the evolution of mammalian reproduction and development

BACKGROUND

We present the genome sequence of the tammar wallaby, Macropus eugenii, which is a member of the kangaroo family and the first representative of the iconic hopping mammals that symbolize Australia to be sequenced. The tammar has many unusual biological characteristics, including the longest period of embryonic diapause of any mammal, extremely synchronized seasonal breeding and prolonged and sophisticated lactation within a well-defined pouch. Like other marsupials, it gives birth to highly altricial young, and has a small number of very large chromosomes, making it a valuable model for genomics, reproduction and development.

RESULTS

The genome has been sequenced to 2 × coverage using Sanger sequencing, enhanced with additional next generation sequencing and the integration of extensive physical and linkage maps to build the genome assembly. We also sequenced the tammar transcriptome across many tissues and developmental time points. Our analyses of these data shed light on mammalian reproduction, development and genome evolution: there is innovation in reproductive and lactational genes, rapid evolution of germ cell genes, and incomplete, locus-specific X inactivation. We also observe novel retrotransposons and a highly rearranged major histocompatibility complex, with many class I genes located outside the complex. Novel microRNAs in the tammar HOX clusters uncover new potential mammalian HOX regulatory elements.

CONCLUSIONS

Analyses of these resources enhance our understanding of marsupial gene evolution, identify marsupial-specific conserved non-coding elements and critical genes across a range of biological systems, including reproduction, development and immunity, and provide new insight into marsupial and mammalian biology and genome evolution.

Reproductive and developmental manipulation of the marsupial, the tammar wallaby Macropus eugenii

The developing marsupial is an ideal animal for use in biomedical research. Marsupials are mammals that have been separated from eutherian mammals for over 130-140 million years. They all deliver altricial young that complete their growth and development after birth usually in a pouch, but not all marsupials have a pouch. Their lactation changes dynamically throughout the period of pouch life, and the mother controls their growth via the production of milk that is tailor-made for each stage of development. The tammar wallaby, Macropus eugenii, has been the experimental marsupial of choice for over five decades, as it is highly amendable to handling and breeds well in captivity. The tammar is especially interesting because it has both a lactational and a seasonal control of its reproduction and embryonic diapause that normally lasts 11 months. Standard molecular techniques can be used for most manipulations in marsupials. However, there are several special techniques for treating the young for experimental surgery and for organ culture that we detail below.

Development of structural and functional connectivity in the thalamocortical somatosensory pathway in the wallaby

Neuronal activity is implicated as a driving force in the development of sensory systems. In order for it to play a developmental role, however, the pathways involved must be capable of transmitting this activity. The relationship between afferent arrival, synapse formation and the onset of chemical neurotransmission has been examined using the advantageous model of a marsupial mammal, the wallaby (Macropus eugenii), to determine at what stage activity has the capacity to influence cortical development. It is known that thalamocortical afferents arrive in the somatosensory cortex on postnatal day (P)15 and that their growth cones reach to the base of the compact cell zone of the cortical plate. However, electronmicroscopy showed that thalamocortical synapses were absent at this stage. Glutamatergic responses were recorded in the cortex following stimulation of the thalamus in slices at this time but only in magnesium-free conditions. The responses were mediated entirely by N-methyl-d-aspartate (NMDA) receptors. From P28, responses could be recorded in normal magnesium and comprised a dominant NMDA-mediated component and a non-NMDA mediated component. At this time thalamocortical synapses were first identified and they were in the cortical plate. By P63 the non-NMDA-mediated component had increased relative to the NMDA-mediated component, and by P70 layer IV began to emerge and contained thalamocortical synapses. By P76 a fast non-NMDA-mediated peak dominated the response. This coincides with the appearance of cortical whisker-related patches and the onset in vivo of responses to peripheral stimulation of the whiskers.

Developmental changes in ventricular myosin isoenzymes of the tammar wallaby

Ventricular myosin in eutherian mammals undergoes a perinatal change in response to a sharp rise in thyroid hormone levels during development. In this investigation, changes in ventricular myosin heavy chains (MyHCs) of the tammar wallaby (Macropus eugenii) from early pouch life to adulthood were analysed using native gel electrophoresis, SDS-PAGE and western blotting. Adult wallaby ventricle showed three myosin isoenzymes, V(1), V(2) and V(3); western blots using specific anti-alpha-MyHC and anti-beta-MyHC antibodies showed their MyHC compositions to be alphaalpha, alphabeta and betabeta, respectively. Ventricular muscle in early pouch joeys expressed predominantly beta-MyHC. Up to 200 days, the time of initial pouch exit, alpha-MyHC content was around 5%. Thereafter, there was a sharp increase of alpha-MyHC expression to 35% by 242 days of age, eventually falling back to 23% in the adult. These changes correlate with known surges in plasma levels of thyroid hormones around pouch exit. The results suggest that ventricular myosins in a marsupial mammal also undergo a developmental change, and that marsupial ventricular myosins are thyroid responsive as in eutherians. The increased alpha-MyHC expression empowers the heart to meet the enhanced cardiovascular demands of out-of-pouch activity and the thermogenic action of thyroid hormones.

Chronic Treatment of Male Tammar Wallabies with Deslorelin Implants During Pouch Life: Effects on Development, Puberty, and Reproduction in Adulthood1

The present study evaluated the effects of chronic GnRH agonist (deslorelin) treatment on sexual maturation in the male tammar wallaby. Slow-release deslorelin or placebo implants were administered to male pouch young (n = 10/group) when they were between 180 and 200 days old, to determine if disruption of the pituitary-testicular axis during development altered the timing of sexual maturation or had long-term effects on adult reproductive function. Deslorelin treatment caused retardation of testicular growth and reduced the serum FSH and testosterone concentrations between 12 and 24 mo of age. Maturation of the hypothalamic-pituitary-testicular axis was also delayed in treated animals at 13 and 19 mo of age. Despite these alterations in the pattern and timing of neuroendocrine development, sexual maturation was not permanently blocked in these animals and deslorelin-treated animals reached sexual maturity at the same age as treated animals, as evidenced by a fully functional pituitary-testicular axis and proven fertility at 25 mo of age. The ability of the treated animals to reach puberty at the same time as control animals, despite delayed maturation of the hypothalamic-pituitary-testicular axis, suggests that puberty in the male tammar wallaby is additionally regulated by other, gonadotropin-independent factors.

Review of surrogacy program for endangered victorian brush-tailed rock wallaby (Petrogale penicillata) with special reference to animal husbandry and veterinary considerations

A surrogacy program to increase the reproductive rate of the critically endangered Victorian brush-tailed rock wallaby (Petrogale penicillata), initially developed in semicaptive conditions, was established in close captivity at Adelaide Zoological Gardens in 1998. Pouch young were removed from their mothers on days 8-20 or 40-45 after parturition and placed onto the teat of a tammar wallaby (Macropus eugenii) or yellow-footed rock wallaby (Petrogale xanthopus xanthopus) surrogate mother. During the early years of the program, mortality of brush-tail pouch young was high (12/16, 75%), both before transfer while still on their mother (5/16) and after transfer to a surrogate mother (7/11). Changing pouch young transfer methodology and improving the health status of the surrogate animals during the later years of the program significantly reduced the mortality of brush-tail pouch young (8/29). Under the new methodology, no mortality of brush-tail pouch young was observed between birth and the time of transfer, (0/29), and after transfer, pouch young mortality rate was eight of 29 (28%). Factors implicated in the improved success of the program included 1) the early transfer (between days 8 and 20) of brush-tail pouch young from mother to surrogate mother, 2) review of the veterinary history and health of the animals selected to act as surrogate mothers, and 3) increased access to grazing pasture for foster mothers. The reproductive rate of the brush-tail females in the later years of the breeding program was sixfold above natural birthing rates. These and other factors important in establishing a breeding program of this nature are discussed.

Reproduction in female swamp wallabies, Wallabia bicolor

The swamp wallaby (Wallabia bicolor) is a common, medium-sized, browsing macropodid marsupial that is unique in many ways. Relatively little is known about the reproductive biology of this species. Previous studies have proposed that the swamp wallaby has a pre-partum oestrus because the gestation period (x = 35.5 days, n = 4) is on average longer than the oestrus period (x = 31.0 days, n = 5) and the period from the removal of pouch young (RPY) to mating (x = 26.0 days, n = 3). In the current study, the period from RPY to birth was confirmed at x = 31.25 days (n = 4) in captive animals, consistent with a pre-partum oestrus. A growth curve for swamp wallaby pouch young was constructed from the progeny of captive animals to estimate the age and date of birth of young in a wild, culled population in South Gippsland, Victoria, and the reproduction of females in the wild throughout the year was examined. Young were born in every month of the year, with no statistically significant variation in the number of young born in each month. Females did not have a period of seasonal anoestrus and conceived throughout the year. Female swamp wallabies in South Gippsland bred continuously throughout the period of this study.

Differential expression of WNT4 in testicular and ovarian development in a marsupial

Background

WNT4 is a key regulator of gonadal differentiation in humans and mice, playing a pivotal role in early embryogenesis. Using a marsupial, the tammar wallaby, in which most gonadal differentiation occurs after birth whilst the young is in the pouch, we show by quantitative PCR during early testicular and ovarian development that WNT4 is differentially expressed ingonads.

Results

Before birth, WNT4 mRNA expression was similar in indifferent gonads of both sexes. After birth, in females WNT4 mRNA dramatically increased during ovarian differentiation, reaching a peak by day 9–13 post partum (pp) when the ovarian cortex and medulla are first distinguishable. WNT4 protein was localised in the ovarian cortex and at the medullary boundary. WNT4 mRNA then steadily decreased to day 49, by which time all the female germ cells have entered meiotic arrest. In males, WNT4 mRNA was down-regulated in testes immediately after birth, coincident with the time that seminiferous cords normally form, and rose gradually after day 8. By day 49, when testicular androgen production normally declines, WNT4 protein was restricted to the Leydig cells.

Conclusion

This is the first localisation of WNT4 protein in developing gonads and is consistent with a role for WNT4 in steroidogenesis. Our data provide strong support for the suggestion that WNT4 not only functions as an anti-testis gene during early development, but is also necessary for later ovarian and testicular function.

A quantitative study of the morphological development and bacterial colonisation of the gut of the tammar wallaby Macropus eugenii eugenii and brushtail possum Trichosurus vulpecula during in-pouch development

We compared the rates of change of various morphological parameters of the stomach, small intestine, caecum and colon of tammar wallabies and brushtail possums with body mass during in-pouch development. These were correlated with changes in the numbers of bacterial species in the various gut segments. In the pouch-young of both species, the wet tissue masses of all gut segments increased with body mass in a positively allometric manner (i.e. with a body mass exponent > 1), suggesting that the mass of each component was disproportionately low at birth, but increased disproportionately rapidly postnatally. However, the lengths of the wallaby stomach and small intestine scaled isometrically with respect to body mass (i.e. with a body mass exponent around 0.33), which may indicate that the shape of these components changes to the adult form during early neonatal development. Conversely, the length of the caecum and colon of both wallabies and possums scaled in a positively allometric manner with respect to body mass, showing area to volume compensation. This may indicate a more general pattern of disproportionately rapid postnatal enlargement in areas that are distal to the principal sites of neonatal digestion (i.e. the stomach). The numbers of bacterial species present in the various gastrointestinal segments of both species were low in animals aged 100 days or less but there was a significant increase in microbial diversity in the caecum of brushtail possums aged over 100 days. The possum caecum also showed the greatest rate of increase in wet tissue mass relative to body mass. It is postulated that caecal development may act as a nidus for establishment of communities of commensal microflora in the developing marsupial.

Postnatal development of orexin-A and orexin-B like immunoreactivities in the Eastern grey kangaroo (Macropus giganteus) hypothalamus

The Eastern grey kangaroo (Macropus giganteus) is a marsupial, which is born in an extremely undeveloped state and has a long suckling period in the mother's pouch. In the present study, we examined the immunoreactivities of orexin-A (OXA) and orexin-B (OXB) in the hypothalamus of the Eastern grey kangaroo during the preweaning period, postweaning period and adulthood. In the preweaning period, only a few OXA- and OXB-like immunoreactive (LI) neurons and fibers were present and the intensity of staining was very weak. In the postweaning period, there was a pronounced increase in the numbers of OXA- and OXB-LI neurons and fibers and the intensity of the immunoreactivity was considerably stronger in comparison to the preweaning period. In the adult, the numbers of OXA- and OXB-LI neurons and fibers appeared to be slightly increased and the intensity was slightly stronger in comparison to the postweaning period. At all time periods, the distributions of OXA- and OXB-LI neurons was similar. The postnatal development of hypothalamic orexin neurons may be associated with developmental changes, including feeding behavior.

Cross-fostering inMacropus eugenii leads to increased weight but not accelerated gastrointestinal maturation

Stomach and small intestine development was characterized in tammar wallaby (Macropus eugenii) pouch young (PY) using both morphological and immunohistological criteria. At birth, the stomach is undeveloped in comparison to the well-developed intestinal mucosa. The stomach maintains a uniform morphology in both the forestomach and hindstomach regions until the specialization of cardiac and gastric glands are seen at PY170. Parietal cells, found throughout the mucosa are downregulated in the forestomach as cardiac glandular stomach is developing prior to the transition of the offspring to a diet that includes herbage. In the small intestine, mature-type villi are present at birth but the muscularis externa is immature and undergoes significant development around PY120 onwards. We investigated the effects of changes in maternal milk on gut development in the tammar wallaby using a cross fostering approach that provided younger pouch young with older stage milk. Younger PY (average age 67 days postpartum, n = 5) were transferred onto teats vacated by older stage PY (average age 100 days postpartum, n = 6) for 34 days before gut development was assessed. In addition milk analysis was performed before and after fostering events. Cross-fostered PY animals receiving older stage milk were found to be 31% heavier than controls. There was no difference between carbohydrate and protein concentrations however, fostered PY milk had a higher concentration of lipid than that of controls that may have contributed to heavier fostered PY. No difference was found in stomach or small intestine development between these groups using the criteria employed in this study.

CD15 immunoreactivity in the developing brain of a marsupial, the tammar wallaby ( Macropus eugenii)

We have studied the distribution of the CD15 epitope in the developing brain of an Australian diprotodontid metatherian mammal, the tammar wallaby ( Macropus eugenii), using immunohistochemistry in conjunction with hematoxylin and eosin staining. At the time of birth (28 days after conception), CD15 immunoreactivity labeled somata in the primordial plexiform layer of the parietal cortex in a similar position to that seen in the early fetal eutherian brain. CD15 immunoreactivity in the brain of the developing pouch-young wallaby was found to be localized on the surface of radial glia at boundaries between developmentally significant forebrain compartments in a similar distribution to that seen in developing eutherian brain. These were best seen in the developing diencephalon, delineating epithalamus, ventral and dorsal thalamus and hypothalamic anlage, and in the striatum. Immunoreactivity for CD15 identified radial glia marking the lateral migratory stream at the striatopallial boundary, peaking in intensity at P19 to P25. From P37 to P54, CD15 immunoreactivity also demarcated patch compartments in the developing striatum. In contrast, CD15 immunoreactivity in hindbrain structures showed some differences from the temporospatial pattern seen in eutherian brain. These may reflect the relatively early brainstem maturation required for the newborn wallaby to be able to traverse the distance from the maternal genital tract to the pouch. The wallaby provides a convenient model for testing hypotheses concerning the role of CD15 in forebrain development because all events in which CD15 may play a critical role in forebrain morphogenesis occur during pouch life, when the young wallaby is accessible to experimental manipulation.

Thyroid function and the development of endothermy in a marsupial, the Tasmanian bettong, Bettongia gaimardi (Demarest 1822)

The Tasmanian bettong (Bettongia gaimardi) is a small rat-kangaroo (marsupial) found only in Tasmania, Australia. The duration of pouch life is 15 weeks. Adults and older young display non-shivering thermogenesis and this paper examines the role of thyroxine in the development of endothermy in pouch young. Free thyroxine (T4) concentrations varied throughout pouch life. The mean (+/-SE) concentration was 6.2+/-1.9 pmol L(-1) in week 7, increased and peaked at 19.2+/-4.3 pmol L(-1) in week 12, and declined to 5.6+/-0.4 pmol L(-1) by week 20. This was similar to adult levels (3.2+/-3.8 pmol L(-1)). These concentrations showed significant differences. From pouch week 12 onwards, T4 injection raised oxygen consumption. Maximum levels of VO2 after T4 injection occurred at weeks 14-15. Although adult levels were lower, the increase in adult oxygen consumption after T4 injection was about 50%. Peak free T4 levels and metabolic responses to nor-adrenalin occur at week 12 and we hypothesize that thyroid hormone may facilitate the development of adrenergic-receptors in this species. The data presented in the paper further attest to the likely important role of the thyroid gland in the development of endothermy in marsupial pouch young.

Comparison of glucose metabolism in in vivo- and in vitro-matured tammar wallaby oocytes and its relationship to developmental potential following intracytoplasmic sperm injection

Although marsupial oocytes undergo nuclear maturation in vitro, there is, at present, no indication of their developmental potential, largely owing to the lack of in vitro fertilisation and related technologies for marsupials. Glucose metabolism has proven a useful indicator of oocyte cytoplasmic maturation and developmental potential in several eutherian species. Therefore, the aims of the present study were to compare: (1) the rates of glycolysis and glucose oxidation in immature, in vitro-matured and in vivo-matured tammar wallaby oocytes; and (2) the metabolic rate of individual oocytes with their ability to form pronuclei after intracytoplasmic sperm injection. The rates of glycolysis measured in immature (2.18 pmol oocyte–1 h–1), in vitro-matured (0.93 pmol oocyte–1 h–1) and in vivo-matured tammar wallaby oocytes (0.54 pmol oocyte–1 h–1) were within a similar range to values obtained in eutherian species. However, unlike the trend observed in eutherian oocytes, the glycolytic rate was significantly higher in immature oocytes compared with either in vivo- or in vitro-matured oocytes (P < 0.001) and significantly higher in in vitro-matured oocytes compared with in vivo-matured oocytes (P < 0.001). No relationship was identified between glucose metabolism and the developmental capacity of oocytes after intracytoplasmic sperm injection when assessed after 17–19 h. Oocytes that became fertilised (two pronuclei) or activated (one or more pronucleus) were not distinguished from others by their metabolic rates. Longer culture after intracytoplasmic sperm injection (e.g. blastocyst stage) may show oocyte glucose metabolism to be predictive of developmental potential; however, culture to the single-cell stage did not reveal any significant differences in normally developing embryos.

Analysis of EphB receptors and their ligands in the developing retinocollicular system of the wallaby reveals dynamic patterns of expression in the retina

The expression of EphB1 and B2 receptors and ephrins-B1, -B2 and -B3 in the retina and superior colliculus of the wallaby (Macropus eugenii) was examined during the development of the retinocollicular projection, using reverse transcription-polymerase chain reaction and immunohistochemistry. There was an early transient differential expression of EphB2 that was higher in ventral retina and restricted to the outer neuroblast layer, whereas a high ventral to low dorsal gradient of ephrin-B2 expression occurred there throughout the study period. However, there was no dorsoventral gradient of receptors or ligands in retinal ganglion cells or a mediolateral gradient of ephrins in the colliculus. These findings suggest a limited role for these molecules in topographic mapping across the mediolateral colliculus in the wallaby. Early in retinal development there is a complementary pattern of expression of ephrin-B1 and -B2 in the outer neuroblast layer that overlaps with expression of EphB2. Ganglion and amacrine cells also express EphB2. As development proceeds subpopulations of putative horizontal and bipolar cells, also expressing EphB2, come to reside in the inner nuclear layer and ephrin-B1 is expressed throughout the outer nuclear layer. At the same time cells expressing ephrin-B2, and subpopulations of horizontal and bipolar cells come to reside in the inner nuclear layer and there is a corresponding decrease in ephrin-B2 expression in the outer nuclear layer. This pattern of coexpression of receptors and ligands suggests a role for them in cell migration and maintenance of laminar boundaries.

Energy requirements of the red kangaroo (Macropus rufus): impacts of age, growth and body size in a large desert-dwelling herbivore

Generally, young growing mammals have resting metabolic rates (RMRs) that are proportionally greater than those of adult animals. This is seen in the red kangaroo ( Macropus rufus), a large (>20 kg) herbivorous marsupial common to arid and semi-arid inland Australia. Juvenile red kangaroos have RMRs 1.5-1.6 times those expected for adult marsupials of an equivalent body mass. When fed high-quality chopped lucerne hay, young-at-foot (YAF) kangaroos, which have permanently left the mother's pouch but are still sucking, and recently weaned red kangaroos had digestible energy intakes of 641+/-27 kJ kg(-0.75) day(-1) and 677+/-26 kJ kg(-0.75) day(-1), respectively, significantly higher than the 385+/-37 kJ kg(-0.75) day(-1) ingested by mature, non-lactating females. However, YAF and weaned red kangaroos had maintenance energy requirements (MERs) that were not significantly higher than those of mature, non-lactating females, the values ranging between 384 kJ kg(-0.75) day(-1) and 390 kJ kg(-0.75) day(-1) digestible energy. Importantly, the MER of mature female red kangaroos was 84% of that previously reported for similarly sized, but still growing, male red kangaroos. Growth was the main factor affecting the proportionally higher energy requirements of the juvenile red kangaroos relative to non-reproductive mature females. On a good quality diet, juvenile red kangaroos from permanent pouch exit until shortly after weaning (ca. 220-400 days) had average growth rates of 55 g body mass day(-1). At this level of growth, juveniles had total daily digestible energy requirements (i.e. MER plus growth energy requirements) that were 1.7-1.8 times the MER of mature, non-reproductive females. Our data suggest that the proportionally higher RMR of juvenile red kangaroos is largely explained by the additional energy needed for growth. Energy contents of the tissue gained by the YAF and weaned red kangaroos during growth were estimated to be 5.3 kJ g(-1), within the range found for most young growing mammals.

The first thalamocortical synapses are made in the cortical plate in the developing visual cortex of the wallaby (Macropus eugenii)

The time course of development and laminar distribution of thalamocortical synapses in the visual cortex of the marsupial mammal the wallaby (Macropus eugenii) has been studied by electron microscopy from the time of afferent ingrowth to the appearance of layer 4, the main target for thalamic axons. Axons were labeled from the thalamus by a fluorescent carbocyanine dye in fixed tissue or by transneuronal transport of horseradish peroxidase conjugated to wheat germ agglutinin from the eye. Thalamic axons first reached the cortex 2 weeks after birth and grew into the developing cortical plate without a waiting period in the subplate. The first thalamocortical synapses were detected 2 weeks later solely throughout the loosely packed zone of the cortical plate, where layer 6 cells previously have been shown to reside. As the thickness of the cortex increased with age, thalamocortical synapses were increasingly prevalent in the loosely packed zone of the cortical plate. With the appearance of layer 4, thalamocortical synapses were found there as well as in the marginal zone and layer 6. There was no evidence for an early population of thalamocortical synapses in the subplate. The first synapses made by thalamic axons were in a region containing layer 6 cells, one of their normal targets in the mature cortex.