A pronounced uterine pro-inflammatory response at parturition is an ancient feature in mammals

Regulating maternal immunity is necessary for successful human pregnancy. Whether this is needed in mammals with less invasive placentation is subject to debate. Indeed, the short gestation times in marsupials have been hypothesized to be due to a lack of immune regulation during pregnancy. Alternatively, the maternal marsupial immune system may be unstimulated in the absence of a highly invasive placenta. Transcripts encoding pro-inflammatory cytokines were found to be overrepresented in the whole uterine transcriptome at terminal pregnancy in the opossum, Monodelphis domestica To investigate this further, immune gene transcripts were quantified throughout opossum gestation. Transcripts encoding pro-inflammatory cytokines remained relatively low during pre- and peri-attachment pregnancy stages. Levels dramatically increased late in gestation, peaking within 12 h prior to parturition. These results mirror the spike of inflammation seen at eutherian parturition but not at attachment or implantation. Our results are consistent with the role of pro-inflammatory cytokines at parturition being an ancient and conserved birth mechanism in therian mammals.

Uterine remodelling during pregnancy and pseudopregnancy in the brushtail possum (Trichosurus vulpecula; Phalangeridae)

The formation of a placenta is critical for successful mammalian pregnancy and requires remodelling of the uterine epithelium. In eutherian mammals, remodelling involves specific morphological changes that often correlate with the mode of embryonic attachment. Given the differences between marsupial and eutherian placentae, formation of a marsupial placenta may involve patterns of uterine remodelling that are different from those in eutherians. Here we present a detailed morphological study of the uterus of the brushtail possum (Trichosurus vulpecula; Phalangeridae) throughout pregnancy, using both scanning and transmission electron microscopy, to identify whether uterine changes in marsupials correlate with mode of embryonic attachment as they do in eutherian mammals. The uterine remodelling of T. vulpecula is similar to that of eutherian mammals with the same mode of embryonic attachment (non-invasive, epitheliochorial placentation). The morphological similarities include development of large apical projections, and a decrease in the diffusion distance for haemotrophes around the period of embryonic attachment. Importantly, remodelling of the uterus in T. vulpecula during pregnancy differs from that of a marsupial species with non-invasive attachment (Macropus eugenii; Macropodidae) but is similar to that of a marsupial with invasive attachment (Monodelphis domestica; Didelphidae). We conclude that modes of embryonic attachment may not be typified by a particular suite of uterine changes in marsupials, as is the case for eutherian mammals, and that uterine remodelling may instead reflect phylogenetic relationships between marsupial lineages.

Stress reactivity, condition, and foraging behavior in zebra finches: effects on boldness, exploration, and sociality

The arid and semi-arid zones of Australia are characterized by highly variable and unpredictable environmental conditions which affect resources for flora and fauna. Environments which are highly unpredictable in terms of both resource access and distribution are likely to select for a variety of adaptive behavioral strategies, intrinsically linked to the physiological control of behavior. How unpredictable resource distribution has affected the coevolution of behavioral strategies and physiology has rarely been quantified, particularly not in Australian birds. We used a captive population of wild-derived zebra finches to test the relationships between behavioral strategies relating to food access and physiological responses to stress and body condition. We found that individuals that were in poorer body condition and had higher peak corticosterone levels entered baited feeders earlier in the trapping sequence of birds within the colony. We also found that individuals in poorer body condition fed in smaller social groups. Our data show that the foraging decisions which individuals make represent not only a trade-off between food access and risk of exposure, but their underlying physiological response to stress. Our data also suggest fundamental links between social networks and physiological parameters, which largely remain untested. These data demonstrate the fundamental importance of physiological mechanisms in controlling adaptive behavioral strategies and the dynamic interplay between physiological control of behavior and life-history evolution.

Mammary cell-activating factor regulates the hormone-independent transcription of the early lactation protein (ELP) gene in a marsupial

The regulation of the tammar wallaby (Macropus eugenii) early lactation protein (ELP) gene is complex. ELP is responsive to the lactogenic hormones; insulin (I), hydrocortisone (HC) and prolactin (PRL) in mammary gland explants but could not be induced with lactogenic hormones in tammar primary mammary gland cells, nor in KIM-2 conditionally immortalised murine mammary epithelial cells. Similarly, ELP promoter constructs transiently-transfected into human embryonic kidney (HEK293T) cells constitutively expressing the prolactin receptor (PRLR) and Signal Transducer and Activator of Transcription (STAT)5A were unresponsive to prolactin, unlike the rat and mouse β-casein (CSN2) promoter constructs. Identification of the minimal promoter required for the hormone-independent transcription of tammar ELP in HEK293Ts and comparative analysis of the proximal promoters of marsupial ELP and the orthologous eutherian colostrum trypsin inhibitor (CTI) gene suggests that mammary cell-activating factor (MAF), an E26 transformation-specific (ETS) factor, may bind to an AGGAAG motif and activate tammar ELP.

Uterine morphology during diapause and early pregnancy in the tammar wallaby (Macropus eugenii)

In mammals, embryonic diapause, or suspension of embryonic development, occurs when embryos at the blastocyst stage are arrested in growth and metabolism. In the tammar wallaby (Macropus eugenii), there are two separate uteri, only one of which becomes gravid with the single conceptus at a post-partum oestrus, so changes during pregnancy can be compared between the gravid and non-gravid uterus within the same individual. Maintenance of the viable blastocyst and inhibition of further conceptus growth during diapause in the tammar is completely dependent on the uterine environment. Although the specific endocrine and seasonal signals are well established, much less is known about the cellular changes required to create this environment. Here we present the first detailed study of uterine morphology during diapause and early pregnancy of the tammar wallaby. We combined transmission electron microscopy and light microscopy to describe the histological and ultrastructural changes to luminal and glandular epithelial cells. At entry into diapause after the post-partum oestrus and formation of the new conceptus, there was an increase in abundance of organelles associated with respiration in the endometrial cells of the newly gravid uterus, particularly in the endoplasmic reticulum and mitochondria, as well as an increase in secretory activity. Organelle changes and active secretion then ceased in these cells as they became quiescent and remained so for the duration of diapause. In contrast, cells of the non-gravid, post-partum, contralateral uterus underwent sloughing and remodelling during this time and some organelle changes in glandular epithelial cells continued throughout diapause, suggesting these cells are not completely quiescent during diapause, although no active secretion occurred. These findings demonstrate that diapause, like pregnancy, is under unilateral endocrine control in the tammar, and that preparation for and maintenance of diapause requires substantial changes to uterine endometrial cell ultrastructure and activity.

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.

Quantifying the impact of development on phenotypic variation and evolution

A primary goal of evolutionary biology is to identify the factors that shape phenotypic evolution. According to the theory of natural selection, phenotypic evolution occurs through the differential survival and reproduction of individuals whose traits are selectively advantageous relative to other individuals in the population. This implies that evolution by natural selection is contingent upon the distribution and magnitude of phenotypic variation among individuals, which are in turn the products of developmental processes. Development therefore has the potential to affect the trajectory and rate of phenotypic evolution. Recent research in diverse systems (e.g., mammalian teeth, cichlid skulls, butterfly wings, and marsupial limbs) supports the hypothesis that development biases phenotypic variation and evolution, but suggests that these biases might be system-specific.

Expression of the mammary gland-specific tammar wallaby early lactation protein gene is maintained in vitro in the absence of prolactin

Marsupial ELP (early lactation protein) and its eutherian orthologue, CTI (colostrum trypsin inhibitor) are expressed in the mammary gland only for the first 100 days postpartum (Phase 2A) in the tammar wallaby and during the bovine and canine colostrogenesis period 24-36h postpartum respectively. The factors which regulate temporal ELP and CTI expression are unknown. A tammar mammary gland explant culture model was used to investigate ELP gene regulation during pregnancy and early- and mid-lactation (Phase 1, 2A and 2B respectively). Tammar ELP expression could only be manipulated in explants in vitro if the gene was already expressed in vivo. ELP expression was maximal in Phase 1 explants treated with lactogenic hormones (insulin, hydrocortisone and prolactin), but unlike LGB (β-lactoglobulin), ELP expression was maintained in insulin or insulin and hydrocortisone over a 12-day culture period. In contrast, ELP was down-regulated when cultured without hormones. ELP could not be induced in explants cultured from mid-lactation which suggested that transcriptional repressors may prevent ELP expression during this period.

The opossum genome: insights and opportunities from an alternative mammal

The strategic importance of the genome sequence of the gray, short-tailed opossum, Monodelphis domestica, accrues from both the unique phylogenetic position of metatherian (marsupial) mammals and the fundamental biologic characteristics of metatherians that distinguish them from other mammalian species. Metatherian and eutherian (placental) mammals are more closely related to one another than to other vertebrate groups, and owing to this close relationship they share fundamentally similar genetic structures and molecular processes. However, during their long evolutionary separation these alternative mammals have developed distinctive anatomical, physiologic, and genetic features that hold tremendous potential for examining relationships between the molecular structures of mammalian genomes and the functional attributes of their components. Comparative analyses using the opossum genome have already provided a wealth of new evidence regarding the importance of noncoding elements in the evolution of mammalian genomes, the role of transposable elements in driving genomic innovation, and the relationships between recombination rate, nucleotide composition, and the genomic distributions of repetitive elements. The genome sequence is also beginning to enlarge our understanding of the evolution and function of the vertebrate immune system, and it provides an alternative model for investigating mechanisms of genomic imprinting. Equally important, availability of the genome sequence is fostering the development of new research tools for physical and functional genomic analyses of M. domestica that are expanding its versatility as an experimental system for a broad range of research applications in basic biology and biomedically oriented research.

Functional respiratory morphology in the newborn quokka wallaby (Setonix brachyurus)

A morphological and morphometric study of the lung of the newborn quokka wallaby (Setonix brachyurus) was undertaken to assess its morphofunctional status at birth. Additionally, skin structure and morphometry were investigated to assess the possibility of cutaneous gas exchange. The lung was at canalicular stage and comprised a few conducting airways and a parenchyma of thick-walled tubules lined by stretches of cuboidal pneumocytes alternating with squamous epithelium, with occasional portions of thin blood-gas barrier. The tubules were separated by abundant intertubular mesenchyme, aggregations of developing capillaries and mesenchymal cells. Conversion of the cuboidal pneumocytes to type I cells occurred through cell broadening and lamellar body extrusion. Superfluous cuboidal cells were lost through apoptosis and subsequent clearance by alveolar macrophages. The establishment of the thin blood-gas barrier was established through apposition of the incipient capillaries to the formative thin squamous epithelium. The absolute volume of the lung was 0.02 +/- 0.001 cm(3) with an air space surface area of 4.85 +/- 0.43 cm(2). Differentiated type I pneumocytes covered 78% of the tubular surface, the rest 22% going to long stretches of type II cells, their precursors or low cuboidal transitory cells with sparse lamellar bodies. The body weight-related diffusion capacity was 2.52 +/- 0.56 mL O(2) min(-1) kg(-1). The epidermis was poorly developed, and measured 29.97 +/- 4.88 microm in thickness, 13% of which was taken by a thin layer of stratum corneum, measuring 4.87 +/- 0.98 microm thick. Superficial capillaries were closely associated with the epidermis, showing the possibility that the skin also participated in some gaseous exchange. Qualitatively, the neonate quokka lung had the basic constituents for gas exchange but was quantitatively inadequate, implying the significance of percutaneous gas exchange.

Establishing long-term colonies of marsupials to provide models for studying developmental mechanisms and their application to fertility control

To study marsupial developmental mechanisms and their application to fertility control, it is necessary to develop reliable procedures for breeding, colony maintenance, reproductive monitoring for obtaining known-age embryos and, if possible, an induced ovulation protocol. These procedures also provide means to enhance conservation of endangered species. Such procedures are examined in the stripe-faced dunnart, an excellent model for developmental analysis, and the common brush-tail possum, an agricultural and ecological pest species in New Zealand that has become a model for fertility control in marsupials. A long-term colony of the stripe-faced dunnart has been in existence for 21 years, and the procedures for its maintenance and continued survival are outlined, and include minimal reproductive contributions from wild-caught animals, and development of an appropriate timetable of development and induced-ovulation protocols. Common brushtail possum colonies are relatively frequent but have regular input from wild-caught animals. Procedures that minimise competition for prized resources and allow successful group housing of possums are outlined. For both species the available development timetables, in vitro techniques and induced ovulation protocols are essential tools for the study of developmental mechanisms and fertility control, respectively, and also have considerable implications for conservation of these and other species.