Reproduction of a marsupial: From uterus to pouch

The extension of mammalian pregnancy required taming inflammation: Independent evolution of extended placentation in the tammar wallaby

In the first live-bearing mammals, pregnancy was likely short and ended with a brief period of inflammatory maternal-fetal interaction. This mode of reproduction has been retained in many marsupials. While inflammation is key to successful implantation in eutherians, a key innovation in eutherians is the ability to switch off this inflammation after it has been initiated. This extended period, in which inflammation is suppressed, likely allowed for an extended period of placentation. Extended placentation has evolved independently in one lineage of marsupials, the macropodids (wallabies and kangaroos), with placentation lasting beyond the 2 to 4 d seen in other marsupial taxa, which allows us to investigate the role of inflammation response after attachment in the extension of placentation in mammals. By comparing gene expression changes at attachment in three marsupial species, the tammar wallaby, opossum, and fat-tailed dunnart, we show that inflammatory attachment is an ancestral feature of marsupial implantation. In contrast to eutherians, where attachment-related (quasi-) inflammatory reaction is even involved in epitheliochorial placentation (e.g., pig), this study found no evidence of a distinct attachment-related reaction in wallabies. Instead, only a small number of inflammatory genes are expressed at distinct points of gestation, including IL6 before attachment, LIF throughout placentation, and prostaglandins before birth. During parturition, a more distinct inflammatory reaction is detectable, likely involved in precipitating the parturition cascade similar to eutherians. We suggest that in wallaby, extended gestation became possible by avoiding an inflammatory attachment reaction, which is a different strategy than seen in eutherians.

Pelage variation and reproduction in the gray short-tailed opossum Monodelphis domestica (Didelphimorphia: Didelphidae)

Marsupials have short gestation periods, with altricial neonates completing their development attached to a teat, a condition that induces remarkable structural changes in the inguinal region of reproductive females. In this study, we analyzed the morphological variation in the inguinal region of female museum specimens of Monodelphis domestica in search for external traits reminiscent of their reproductive condition when collected. We examined 427 taxidermied skins of wild females from northeastern Brazil and classified their inguinal region by color, density of fur, shape, and the presence of spots and teats. We determined relative age based on tooth eruption and wear, to infer the chronological order of inguinal changes. These conditions were computed for each age class and for each month over 4 years for samples from two mesoregions in northeastern Brazil, identified from climatic characteristics. Four distinct morphological patterns recognized in the inguinal region of females were associated with the following reproductive conditions: 1) non-lactating: general shape of the pelvic region indistinct from the rest of body (straight), inguinal region lacking teats, same fur density and color (grayish) as the rest of the body; 2) pre-lactating: pelvic and inguinal regions similar to non-lactating, but yellowish fur and presence of small teats; 3) early-lactating: inguinal region with well-developed teats, fur yellowish (rarely whitish) and less dense, and form of the pelvic region rounded; and 4) late or post-lactating: inguinal region with well-developed teats and dark orange and less dense fur, pelvic region rounded. Lactating females were only recorded from age class 4 on. We also found indications that pelage changes in the inguinal region do not revert after reproduction in the wild. Monthly frequencies of the different conditions recorded for lactating females corroborate previous studies that suggested that M. domestica breeds all year long in northeastern Brazil.

Marsupiais caracterizam-se por apresentar um curto período de gestação, com neonatos altriciais completando seu desenvolvimento ligados à teta, uma condição que induz mudanças estruturais marcantes na região inguinal de fêmeas reprodutivas. No presente estudo analisamos a variação morfológica da região inguinal de fêmeas taxidermizadas de Monodelphis domestica, buscando traços reminiscentes de suas condições reprodutivas quando coletadas. Examinamos 427 peles taxidermizadas de fêmeas silvestres obtidas no Nordeste do Brasil, e classificamos a região inguinal pela cor, densidade de pelos, presença de manchas e tetas, e forma da região pélvica. Determinamos a idade relativa com base na erupção e no desgaste dentário, para inferir a ordem cronológica das mudanças inguinais. Essas condições foram registradas para cada idade e por cada mês ao longo de 4 anos para amostras de duas mesorregiões no Nordeste do Brasil, identificadas com base em características climáticas. Quatro padrões morfológicos distintos reconhecidos na região inguinal das fêmeas foram associadas às seguintes condições reprodutivas: 1) não-lactante: forma geral da região pélvica indistinta do resto do corpo (retas), região inguinal sem tetas e mesma cor e densidade da pelagem (cinza) que o resto do corpo; 2) pré-lactante: regiões inguinal e pélvica similares às do padrão não-lactante, mas pelagem amarelada e presença de tetas pequenas; 3) lactante inicial: região inguinal com tetas bem desenvolvidas, pelagem inguinal amarelada (raramente branca) e menos densa, forma da região pélvica arredondada; 4) lactante tardia ou pós-lactante: região inguinal com tetas bem desenvolvidas, pelagem laranja escura e menos densa, região pélvica arredondada. Fêmeas lactantes foram observadas apenas da classe de idade 4 em diante. Encontramos evidências de que a mudança da pelagem na região inguinal não é revertida depois da reprodução na natureza. Frequências mensais das diferentes condições reprodutivas das fêmeas observadas corroboram estudos prévios que sugerem que M. domestica pode se reproduzir ao longo de todo o ano no Nordeste do Brasil.

The tammar wallaby: a non-traditional animal model to study growth axis maturation

Maturation of the growth hormone (GH)/insulin-like growth factor 1 (IGF1) axis is a critical developmental event that becomes functional over the peripartum period in precocial eutherian mammals such as sheep. In mice and marsupials that give birth to altricial young, the GH/IGF1 axis matures well after birth, suggesting that functional maturation is associated with developmental stage, not parturition. Recent foster-forward studies in one marsupial, the tammar wallaby (Macropus eugenii), have corroborated this hypothesis. 'Fostering' tammar young not only markedly accelerates their development and growth rates, but also affects the timing of maturation of the growth axis compared with normal growing young, providing a novel non-traditional animal model for nutritional manipulation. This review discusses how nutrition affects the maturation of the growth axis in marsupials compared with traditional eutherian animal models.

The value of eutherian-marsupial comparisons for understanding the function of glucocorticoids in female mammal reproduction

This article is part of a Special Issue "SBN 2014". Chronic stress is known to inhibit female reproductive function. Consequently, it is often assumed that glucocorticoid (GC) concentrations should be negatively correlated with reproductive success because of the role they play in stress physiology. In contrast, a growing body of evidence indicates that GCs play an active role in promoting reproductive function. It is precisely because GCs are so integral to the entire process that disruptions to adrenal activity have negative consequences for reproduction. The goal of this paper is to draw attention to the increasing evidence showing that increases in adrenal activity are important for healthy female reproduction. Furthermore, we outline several hypotheses about the functional role(s) that GCs may play in mediating reproduction and argue that comparative studies between eutherian and marsupial mammals, which exhibit some pronounced differences in reproductive physiology, may be particularly useful for testing different hypotheses about the functional role of GCs in reproduction. Much of our current thinking about GCs and reproduction comes from research involving stress-induced levels of GCs and has led to broad assumptions about the effects of GCs on reproduction. Unfortunately, this has left a gaping hole in our knowledge about basal GC levels and how they may influence reproductive function, thereby preventing a broader understanding of adrenal physiology and obscuring potential solutions for reproductive dysfunction.

GRB10 imprinting is eutherian mammal specific

GRB10 is an imprinted gene differently expressed from two promoters in mouse and human. Mouse Grb10 is maternally expressed from the major promoter in most tissues and paternally expressed from the brain-specific promoter within specific regions of the fetal and adult central nervous system. Human GRB10 is biallelically expressed from the major promoter in most tissues except in the placental villus trophoblast where it is maternally expressed, whereas the brain-specific promoter is paternally expressed in the fetal brain. This study characterized the ortholog of GRB10 in a marsupial, the tammar wallaby (Macropus eugenii) to investigate the origin and evolution of imprinting at this locus. The protein coding exons and predicted amino acid sequence of tammar GRB10 were highly conserved with eutherian GRB10. The putative first exon, which is located in the orthologous region to the eutherian major promoter, was found in the tammar, but no exon was found in the downstream region corresponding to the eutherian brain-specific promoter, suggesting that marsupials only have a single promoter. Tammar GRB10 was widely expressed in various tissues including the brain but was not imprinted in any of the tissues examined. Thus, it is likely that GRB10 imprinting evolved in eutherians after the eutherian-marsupial divergence approximately 160 million years ago, subsequent to the acquisition of a brain-specific promoter, which resides within the imprinting control region in eutherians.

The hypothalamic-pituitary-ovarian axis and manipulations of the oestrous cycle in the brushtail possum

The main purpose of this review is to provide a comprehensive update on what is known about the regulatory mechanisms of the hypothalamic-pituitary-ovarian axis in the brushtail possum, and to report on the outcomes of attempts made to manipulate by hormonal means, these processes in the possum. Over the last 15 years, several unique features of possum reproductive physiology have been discovered. These include an extended follicular phase despite elevated concentrations of FSH during the luteal phase, and early expression of LH receptors on granulosa cells of small antral follicles, suggesting a different mechanism for the selection of a dominant follicle. The use of routine synchronisation protocols that are effective in eutherians has failed to be effective in possums, and so the ability to reliably synchronise oestrus in this species remains a challenge.

Evolution of genomic imprinting: insights from marsupials and monotremes

Parent-of-origin gene expression (genomic imprinting) is widespread among eutherian mammals and also occurs in marsupials. Most imprinted genes are expressed in the placenta, but the brain is also a favored site. Although imprinting evolved in therian mammals before the marsupial-eutherian split, the mechanisms have continued to evolve in each lineage to produce differences between the two groups in terms of the number and regulation of imprinted genes. As yet there is no evidence for genomic imprinting in the egg-laying monotreme mammals, although these mammals also form a placenta (albeit short-lived) and transfer nutrients from mother to embryo. Therefore, imprinting was not essential for the evolution of the placenta and its importance in nutrient transfer but the elaboration of imprinted genes in marsupials and eutherians is associated with viviparity. 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.

Society for Reproductive Biology Founders' Lecture 2006 - life in the pouch: womb with a view

Marsupials give birth to an undeveloped altricial young after a relatively short gestation period, but have a long and sophisticated lactation with the young usually developing in a pouch. Their viviparous mode of reproduction trades placentation for lactation, exchanging the umbilical cord for the teat. The special adaptations that marsupials have developed provide us with unique insights into the evolution of all mammalian reproduction. Marsupials hold many mammalian reproductive 'records', for example they have the shortest known gestation but the longest embryonic diapause, the smallest neonate but the longest sperm. They have contributed to our knowledge of many mammalian reproductive events including embryonic diapause and development, birth behaviour, sex determination, sexual differentiation, lactation and seasonal breeding. Because marsupials have been genetically isolated from eutherian mammals for over 125 million years, sequencing of the genome of two marsupial species has made comparative genomic biology an exciting and important new area of investigation. This review will show how the study of marsupials has widened our understanding of mammalian reproduction and development, highlighting some mechanisms that are so fundamental that they are shared by all today's marsupial and eutherian mammals.

Parturition and perfect prematurity: birth in marsupials

Marsupials are distinguished from eutherian mammals in their mode of reproduction. They give birth to a highly altricial young, which completes its development whilst attached to a teat, usually within a pouch. The marsupial neonate has relatively well-developed digestive, respiratory and circulatory systems but retains its fetal excretory system with a fully functional mesonephric kidney and undifferentiated gonads and genitalia. We have investigated birth in the tammar wallaby (Macropus eugenii) and shown that the tiny (400 mg) fetus determines the time of its own delivery. Although plasma progesterone falls, and oestradiol associated with the postpartum oestrus typically rises, around the time of parturition, neither hormone is essential for the timing of birth. However relaxin may loosen the connective tissue of the cervix and vaginae for birth. Labour starts suddenly and is completed within minutes. Both prostaglandins and mesotocin are essential for the contractions that deliver the young. Prostaglandins from the reproductive tract act via the brain to control parturient behaviour. In the last 2 days of gestation fetal adrenal glucocorticoid production increases, promoting lung maturation and surfactant production and ultimately triggering labour. The accessibility of the altricial neonatal marsupial provides a unique opportunity for experimental manipulation of organ development and maturation.

Genomic imprinting of IGF2, p57(KIP2) and PEG1/MEST in a marsupial, the tammar wallaby

Genomic imprinting is widespread amongst mammals, but has not yet been found in birds. To gain a broader understanding of the origin and significance of imprinting, we have characterized three genes, from three separate imprinted clusters in eutherian mammals in the developing fetus and placenta of an Australian marsupial, the tammar wallaby Macropus eugenii. Imprinted gene orthologues of human and mouse p57(KIP2), IGF2 and PEG1/MEST genes were isolated. p57(KIP2) did not show stable monoallelic expression suggesting that it is not imprinted in marsupials. In contrast, there was paternal-specific expression of IGF2 in almost all tissues, but the biased paternal expression of IGF2 in the fetal head and placenta, demonstrates the occurrence of tissue-specific imprinting, as occurs in mice and humans. There was also paternal-biased expression of PEG1/MESTalpha. The differentially methylated region (DMR) of the human and mouse PEG1/MEST promoter is absent in the wallaby. These data confirm the existence of common imprinted regions in eutherians and marsupials during development, but suggest that the regulatory mechanisms that control imprinted gene expression differ between these two groups of mammals.

The marsupial placenta: a phylogenetic analysis

The structure, physiology, and endocrinology of the yolk sac placenta of different marsupial groups is compared and phylogenetically analyzed to provide information on placental characters in the marsupial stem species. We conclude that the marsupial stem species possessed a functional yolk sac placenta. Histotrophic nutrition by uterine secretion decreased during late pregnancy and at least half of the yolk sac was vascularized at the time of shell coat rupture. Due to yolk sac fusion, the larger part of the avascular, bilaminar yolk sac could not serve as a placenta at late gestation in the polyovular marsupial stem species. The bilaminar yolk sac gained a relatively greater importance for nutrition in monovular australidelphians. In macropodids a greater proportion of the yolk sac remained bilaminar at the time of shell coat rupture than in the stem species. Another derived feature of macropodids is the sustained plasma progesterone synthesis that is in turn responsible for an extended secretory phase of the uterus and a lengthened gestation. The placenta of the marsupial stem species was probably capable of metabolising histo- and hemotrophes. Recognition of pregnancy during early stages of development is a derived character of macropodids that we suggest did not occur in the marsupial stem species. However, birth and birth behaviour were apparently induced by prostaglandins in the marsupial stem species. Although the yolk sac formed the definitive placenta, it is likely that the allantois provided a supplementary placental function in the marsupial stem species, but that the role of the allantois became progressively less important during the evolution of marsupial placentation.

c-fos mRNA expression associated with PGF(2alpha)-induced nest-building behaviour in female pigs

Domestic pigs, Sus scrofa, build a maternal nest on the day before parturition. A model for nest building has been established in pigs, in which exogenously administered prostaglandin (PG) F(2alpha) may be used to elicit nesting behaviour in cyclic, pseudopregnant and pregnant pigs. The central mechanisms mediating this response are unknown. The present study determined regional brain activity using semi-quantitative analysis of c-fos mRNA, after induction of nest-building behaviour by PGF(2alpha) in Large White pseudopregnant pigs. Oestradiol valerate injections (5 mg/day) were given on days 11-15 of the oestrous cycle to induce pseudopregnancy. The pigs were housed individually in pens (2.8 x 1.7 m) containing straw. On the test day (day 46 or 47 of pseudopregnancy) animals were injected with 3 ml saline (n=5) or 15 mg of PGF(2alpha) (Lutalyse, Upjohn; n=6) intramuscularly. Pigs treated with PGF(2alpha), but not saline, displayed bouts of rooting, pawing and gathering straw, which we interpret as nest building behaviour. The pigs were killed 65 min after treatment, which was 30 min after peak nest building activity, and the brain, uterus and ovaries removed for processing using in situ hybridisation. Saline-treated pigs had elevated levels of c-fos mRNA, compared to background, in the pituitary, corpus luteum and uterus, and a lower, but elevated, level of expression in cerebellum, cortex, hippocampus and olfactory bulb. PGF(2alpha)-treated pigs had significantly higher levels of c-fos mRNA expression than saline-treated pigs in the parvocellular and magnocellular regions of the hypothalamic paraventricular nucleus, the supraoptic nucleus (including the pars dorso-medialis), the neural lobe of the pituitary gland and the cerebellum. PGF(2alpha)-treated pigs also had significantly higher c-fos induction in corpus luteum. These data show that the pattern of c-fos mRNA expression in specific brain areas is different between pigs that show PGF(2alpha)-induced nest building and saline-injected controls.

Effects of prostaglandin F2alpha treatment on the behavior of pseudopregnant pigs in an extensive environment

In seminatural environments, prepartum sows leave the herd and construct a maternal nest (a dug out hollow lined with vegetation) prior to the birth of their piglets. The endocrine drives motivating this behavior are not understood, but may involve prostaglandin (PG) F2alpha. This study examined the effect of PGF2alpha treatment on the behavior of pseudopregnant gifts housed in a large enclosure. Pseudopregnancy was induced using 5 mg/ml estradiol valerate/day im from days 11 to 15 of the estrous cycle (first day of estrus = day 0). The gifts' behavior was recorded on a control day, during which no treatment was given, and a test day (= 45.9 +/- 0.42 days of pseudopregnancy) when gilts received either 15 mg PGF2alpha (dinoprost: Lutalyse, Upjohn, Crawley, UK, n = 11) or 0.9% saline (n = 10) im at 11.00 h. PGF2alpha-treated gilts traveled further and were more frequently >10 m from the nearest pig than saline-treated animals. In the hour following injection, PGF2alpha-treated animals also showed increased frequencies of rooting and pawing the ground and stood for longer than saline-treated animals. However, gathering and carrying nest materials were not increased. These results suggest that PGF2alpha, given as a single dose to extensively housed gilts, initiated many, but not all, of the behaviors characteristic of prepartum nest building. The dose and duration of PGF2alpha treatment may have limited the observed behaviors. In addition, environmental feedback is likely to affect the degree to which some nest building behaviors are expressed.

Production of prostaglandin f2alpha and its metabolite by endometrium and yolk sac placenta in late gestation in the tammar wallaby, Macropus Eugenii

In this study, we investigated production of prostaglandin (PG) F2alpha and its metabolite, PGFM, by uterine tissues from tammar wallabies in late pregnancy. Endometrial explants were prepared from gravid and nongravid uteri of tammars between Day 18 of gestation (primitive streak) and Day 26.5 (term) and were incubated in Ham's F-10 medium supplemented with glutamine and antibiotics for 20 h. PGF2alpha and PGFM in the medium were assayed by specific, validated RIAs. Control tissues (leg muscle) did not produce detectable amounts of either PG. Both gravid and nongravid endometria secreted PGF2alpha, and production increased significantly in both gravid and nongravid uteri towards term. PGFM was produced in small amounts by both gravid and nongravid uteri, and the rate of production did not increase. Neither oxytocin nor dexamethasone stimulated PG production in vitro in any tissue at any stage. Thus, the surge in peripheral plasma PGFM levels seen at parturition may arise from increased uterine PG production, but further study is needed to define what triggers this release.

Mesotocin receptors during pregnancy, parturition and lactation in the tammar wallaby

Mestocin receptor concentrations in membrane preparations from reproductive tissues of the tammar Macropus eugenii throughout gestation and lactation were assessed using [3H]-oxytocin as the ligand. There was a single binding site which bound both mesotocin and oxytocin with high and similar affinities. Mesotocin receptor concentrations in the myometrium were low (708 +/- 199 fmol mg-1 protein) in early and middle gestation but increased significantly on day 23 of pregnancy of the 26-day gestation period to 1921 +/- 552 fmol mg-1 protein. Myometrial receptors reached a peak of 2483 +/- 575 fmol mg-1 protein on days 25 and 26 of gestation, but returned to basal levels about an hour after birth. Receptor concentrations in the contralateral non-gravid uterus were much lower (605 +/- 75 fmol mg-1) and did not significantly increase throughout the period of gestation but dropped one day before birth. Mesotocin receptors were undetectable in the endometrium, the yolk sac placenta and the lateral, median and anterior vagina of all animals tested. In the lactating mammary gland after birth mesotocin receptors were initially high (588 +/- 38 fmol mg-1) but decreased after 200 days and by late lactation were 224 +/- 55 fmol mg-1 protein on day 240, close to the time of weaning. Mesotocin receptors in the ipsilateral non-lactating gland were also high in early lactation (430 +/- 153 fmol mg-1) and declined in late lactation (62 +/- 20 fmol mg-1). The changing concentrations of mesotocin receptors in pregnancy and lactation demonstrate that they are specifically regulated in tammar reproductive tissues. The increase in mesotocin receptors in gravid, but not in the non-gravid myometrium three days before birth may make the uterus responsive to the surge of mesotocin at birth. Since this rise is unilateral and only occurs in the gravid myometrium it must be due to local effects from the ipsilateral ovary or the feto-placental unit. Likewise, the down-regulation of mesotocin receptors in the contralateral, non-gravid myometrium may be due to its proximity to the developing follicle. The changing concentrations in the lactating and the adjacent, non-lactating mammary gland also reflect a differential regulation of mesotocin receptors, probably mediated via the sucking stimulus. Thus, local influences appear to be of primary importance in the regulation of mesotocin receptors during reproduction in this marsupial.