M B Renfree

..Thus, genomic imprinting could evolve from a defence mechanism against transposable elements that depended on DNA methylation established in germ cells...

..The sequencing of the kangaroo genome provides an opportunity to use comparative analyses to compare the HOX clusters of a mammal with a distinct body plan to those of other mammals...

..abstract:..

..Additionally, in marsupials the zona pellucida is surrounded by two acellular layers, the mucoid coat and shell, which are formed from secretions from the reproductive tract...

....

..We investigated the expression of two genes, HOXA13 and HOXD13, that are crucial for digit patterning in mice during formation of the limbs of the tammar wallaby...

..The recent release of the platypus genome has provided the first opportunity to perform comparisons between prototherian (monotreme; which appear to lack imprinting) and therian (marsupial and eutherian; which have imprinting) mammals...

..abstract:..

..Here, we used pyrosequencing to compare the transcriptomes of a cervical and thoracic thymus from a single 178 day old tammar wallaby...

..In mice, Phlda2 is a dose-sensitive negative regulator of placental growth, as Cdkn1c is for embryonic growth...

..The CDKN1C and IGF2 genes are both imprinted and syntenic in the mouse and human, but in marsupials only IGF2 is imprinted. This study examines the evolution of features that, in eutherians, regulate CDKN1C imprinting...

..We therefore studied the TGIF family in the tammar wallaby (a marsupial mammal) to investigate their roles in reproduction and how and when these genes may have evolved their functions and chromosomal locations...

..The disease is characterised by severe mental retardation, mild alpha-thalassemia, microcephaly, short stature, facial, skeletal, genital and gonadal abnormalities...

..Here we assess the effect of exogenous oestrogen on the molecular pathways of mammalian gonadal development...

..There is currently no evidence for genomic imprinting in the egg-laying monotreme mammals. However, since these mammals do have a short-lived placenta, imprinting appears to be correlated with viviparity but not placentation...

..The opossum genome has turned up several surprises and provided critical new information on the evolution of mammalian genomes...

..Here we review the recent analyses of imprinted gene clusters in marsupials and monotremes, which have served to shed light on the origin and evolution of imprinting mechanisms in mammals...

..Virilization of the Wolffian ducts occurred during an early but short-lived window of sensitivity. This study provides the first clear evidence that under physiological conditions virilization can be mediated by circulating androgen...

..Comparative platypus genome analyses of orthologous imprinted regions have provided strong support for the host defence hypothesis to explain the origin of imprinting...

..Marsupials are certainly placental mammals. However marsupials have an additional trick in their pouches, with the physiologically sophisticated and extended lactation that has allowed them to exchange the umbilical cord for the teat...

....

..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...

..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...

..These results confirm that estrogen can inhibit early testicular development, and that testis determination occurs during a narrow window of time...

..At birth, the marsupial neonate has a well-developed digestive, respiratory and circulatory system, but retains its fetal excretory system with a fully functional mesonephric kidney and undifferentiated gonads and genitalia...

..Our data suggest that WT1 has a conserved function in both the somatic and germ cell lineages of the gonads of marsupials...

..This contraceptive system appears to offer a method of population control for the management of overabundant captive and selected wild populations of macropodid marsupials...

..It is not detectable in atretic follicles. Collectively, these studies suggest that AMH expression has been conserved during mammalian evolution and is intimately linked to upstream sex determination mechanisms...

..The increased oxidation results in greater ATP production, which plausibly fuels the increased energy requirements of wallaby blastocysts during the early stages of reactivation...

....

..Semen quality may also improve in response to an increase in the number of available oestrous females...

....

..It is possible that the quiescent tammar endometrial environment has an inhibitory factor necessary to maintain diapause in the tammar blastocyst...

....

..We conclude that oestrogen alone is not capable of stimulating normal growth of blastocysts, and its role during early pregnancy in tammars remains unclear...

..The ability of estradiol to cause testis-to-ovary sex reversal in marsupials provides a new way of studying the interactions between genes and hormones in testicular differentiation...

....

....

..Frequent rearrangement of the X, along with the absence of a marsupial XIST gene, suggests that inactivation of the marsupial X chromosome does not depend on a whole-chromosome repression by a control locus...

....

..p. We conclude that the presence of AR is not the initiating signal for virilization of the UGS in this marsupial male...

....

..These observations suggest that FGF9 promotes male fate in the early gonad of marsupials through an antagonistic relationship with WNT4 as it does in eutherian mammals...

..There is no doubt that future research will strengthen this contribution, but we are faced with serious conservation questions that must be solved if we are to maintain these wonderful animals as a resource for future generations...

..The evidence from our embryological study of the elephant also suggests that it evolved from an aquatic mammal...

....

..This study suggests that there is an early window of time before day 60 when androgen imprinting must occur for normal penile development and closure of the urethral groove...

..Therefore, the tammar wallaby may provide a useful experimental model animal in which to investigate the hormonal control of testicular migration and closure of the inguinal canal...

..4 +/- 0.3 pmol per embryo h-1). It is likely that metabolism of amino acids and fatty acids contributes to the energy supply during reactivation of tammar wallaby blastocysts after embryonic diapause...

..There is no evidence for a Y-borne ATRX homologue in mouse or human, implying that this gene has been lost in eutherians and its role supplanted by the evolution of SRY from SOX3 as the dominant determiner of male differentiation...

..This study examines the role of IGF2 in the yolk sac placenta of the tammar wallaby, Macropus eugenii...

..We propose that milk from later stages of lactation and/or herbage consumed by the PY may play independent roles in regulating these two processes...

..These data show that exon 3 was inserted into the GH-R after the divergence of the marsupial and eutherian lineages at least 130 million years ago...

....

..The extended secretory phase of the tammar uterus and the maternal recognition of early pregnancy appear to be derived characters of macropodid marsupials...

..Tammars have a hopping mode of locomotion and, like humans, are essentially bipedal. We suggest that inguinal closure evolved in these two species because their upright posture may otherwise lead to a high incidence of inguinal hernias...

..Thus, the yolk sac of humans, like that of all viviparous mammals, is a true placenta crucial for early embryonic development and survival...

..These results demonstrate an early onset of gastric ghrelin expression in the tammar in concert with a functional stomach at a relatively earlier stage than that of developmentally more mature eutherian young...

..This further strengthens the hypothesis that 5alpha-adiol is the circulating androgen responsible in this species for virilization during development...

..Collectively these studies have led to the development of new paradigms to explain the hormonal mechanisms mediating sexual differentiation...

..This study uses comparative cross species sequence and functional analyses between humans and a marsupial (the tammar wallaby,Macropus eugenii) to refine the mammalian Wnt4 promoter...

..The receptors can respond to exogenous estrogen at this early stage and are capable of transducing signals in the early mammalian gonad. However, the selective forces that maintained conserved ER expression in this tissue remain unknown...

....

..This confirms that the male's reproductive state is dependent on a signal from females and is not blocked through seasonal effects...

..Thus, unlike POU5F1, the role of POU2 may not be restricted to pluripotent cell types but could have a related function such as maintaining multipotency in adult stem cells...

..Females in the area conceived year-round, suggesting that seasonal changes in the male reproductive tract did not prevent at least some males from breeding throughout the year...

..We propose an hypothesis that an augmented thyroid hormone distributor protein network contributes to the rise in total thyroid hormone levels in the blood during development...

..However, blastomeres were more closely apposed in embryos from tubal oocytes and cell-cell adhesion was more pronounced, indicating that the mucoid coat may be involved in maintaining the integrity of the conceptus during cleavage...

....

..We conclude that dihydrotestosterone, largely formed in the tissue by the oxidation of androstanediol derived from the testes and also the 5alpha-reduction of testosterone, is responsible for Wolffian duct virilization in this species...

..The conservation and loss of particular motifs identify those required for testicular function (ATRY) and function in other tissues (ATRX)...

..Alignment of vertebrate ATRX sequences highlights other conserved elements, including a negatively charged mammalian sequence which we propose to be involved in binding of positively charged histone tails...

....

..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...

....

..These results suggest that levonorgestrel inhibits the preovulatory surge of luteinising hormone...

..These previously undescribed locations of SOX9 expression suggest that SOX9 may play additional roles in the differentiation of the marsupial reproductive system...

..This robust approach represents a new tool for isolating unknown sequence under challenging cloning scenarios such as poor library representation, long coding regions, long 3' untranslated regions, and difficult template regions...

....

..There is thus a strong case that fetal adrenal cortisol plays a key role in the preparation for birth and the timing of it. Further studies are in progress to more clearly define the mechanisms behind these actions of cortisol...

..Our data demonstrate that electron-dense granules in the luteal cell cytoplasm of a pregnant marsupial contain relaxin. The peptide is produced in greatest amounts at the end of pregnancy, consistent with a role in parturition...

....

..The degree of vomeronasal organ development makes it likely that, as in other mammals, pheromones are important in the reproduction of the tammar...

..The restriction of imprinting to the yolk sac suggests that imprinting of INS evolved in the chorio-vitelline placenta independently of other tissues in the therian ancestor of marsupials and eutherians...

..p.). In contrast with the polyovular dasyurid and didelphid marsupials, the tammar wallaby ejaculates large numbers of spermatozoa, but transport is relatively inefficient and sperm storage in the tract before ovulation is limited...

....

..These data suggest that modifications to Sertoli cell function resulting from testicular cooling create an environment that is unable to support spermatogenesis by donor germ cells...

..Thus, levonorgestrel implants provide a safe, highly effective and long-term method of fertility control for macropodid marsupials and should be applicable for the management of overabundant captive and selected wild populations...

..We conclude that expression of steroid 5alpha-reductase in the developing wallaby testes allows formation of 5alpha-reduced androgens by a pathway that does not involve testosterone as an intermediate...

..Etonogestrel had absolutely no contraceptive effect at the two doses delivered and so is not suitable for controlling koala populations. In contrast, levonorgestrel was effective as a long-term, reversible contraceptive in wild koalas...

..p.) but with highly motile spermatozoa. These young represent the first macropodids born by AI and the first marsupials conceived using epididymal spermatozoa...

..The absence of expression in the developing gonad strongly suggests that SOX3 does not have a conserved role in mammalian sexual determination or differentiation...

..As demonstrated in the tammar wallaby, cold storage has potential as a method for storage and transport of marsupial ovaries up to 24 h...

..These results provide a basis for developing culture conditions for longer term development of marsupial embryos in vitro...

..Although the dominant males gained most first matings and individually sired half of the offspring, the subdominant males still contributed significantly to the population, at least in captivity...

..Morphologically normal rat and mouse spermatozoa were present in the epididymis and vas deferens of the recipient rats. This highlights the potential for transplantation of male germ cells between different species...

..Sequencing of this genome now provides a valuable resource for deep mammalian comparative analyses, as well as for monotreme biology and conservation...

....

..The conservation in all therians of the mechanism controlling imprinting of the IGF2-H19 locus suggests a sequential model of imprinting evolution...

..Thus, the evolution of imprinting in viviparous mammals is ongoing...

..A recent mammal-specific retrotransposition event led to the formation of a completely new gene only in the eutherian domain, which may have driven imprinting at the cluster...