Yolanda P. Cruz

Progesterone receptor in the forebrain of female gray short-tailed opossums: Effects of exposure to male stimuli

Progesterone receptor immunoreactivity (PRir) in brain areas involved in reproductive behavior in eutherian species was examined for the first time in a female marsupial, the gray short-tailed opossum (Monodelphis domestica, hereinafter, opossum). PRir in nuclei of neurons, measured as area covered by stained nuclei, was seen in the arcuate nucleus (Arc); anteroventral periventricular nucleus (AVPv); bed nucleus of the stria terminalis (BST); medial preoptic area (MPOA), and ventromedial hypothalamus (VMH), but not in control areas adjacent to the hypothalamus or cortex. Female opossums are induced into cytological, urogenital sinus (UGS), estrus by male pheromones and into behavioral estrus, i.e., receptivity, by pairing with a male, and both estradiol (E) and progesterone (P) are involved in induction of receptivity in intact and ovariectomized females. PRir in the AVPv, MPOA, and VMH was very low in females that had never been exposed to males or their scent marks, i.e., naïve anestrous (NVA) females, and either previous or current exposure to males or their scent marks was associated with elevated PRir. PRir was significantly higher in the AVPv and MPOA of anestrous females with previous but no current exposure to males and their scent marks, i.e., experienced anestrous (EXPA) females, than in NVA females, but PRir was significantly lower in the MPOA and VMH of EXPA females than in females that were behaviorally receptive and had recently copulated, i.e., behavioral receptive estrous (BRE) females. PRir was higher in the VMH of both UGS estrous (UGSE) and BRE females compared to that in EXPA animals, but PRir did not differ between UGSE and BRE females in any of the 3 brain areas examined, including the MPOA These results provide evidence that pheromonal induction of estrus and sexual receptivity in opossums is associated with elevation of PRir in the VMH and MPOA and that prior exposure to males or their pheromones, even in the absence of current male stimuli, is associated with persistent elevation of PRir in the AVPv and MPOA.

Expression patterns of Oct4, Cdx2, Tead4, and Yap1 proteins during blastocyst formation in embryos of the marsupial, Monodelphis domestica Wagner

The marsupial blastocyst forms in an entirely different manner from its eutherian counterpart, involving cell–zona rather than cell–cell adhesion during the 8‐ to‐16‐cell transition. While the eutherian blastocyst consists of a spherical trophoblast completely enveloping a pluripotent inner cell mass, or pluriblast, the marsupial blastocyst forms initially as a bowl‐shaped monolayer of cells lining the zona pellucida at the embryonic pole (ep). This monolayer contains a small patch of centrally positioned pluriblast cells edged with trophoblast cells that later coalesce at the abembryonic pole. Using immunocytochemistry, we examined the localization of the proteins Oct4, Cdx2, Tead4, Sox2, and Yap1 in opossum embryos to determine if their temporal expression pattern differed from that in the mouse, given the important differences in cell behavior preceding blastocyst formation in these mammals. Our results indicate that these proteins are expressed in similar temporal patterns despite the topological differences between mouse and opossum cleavage‐stage embryos and blastocysts. That the Hippo‐pathway protein Yap1 localized specifically around the approximately 128‐cell stage to opossum trophoblast nuclei but remained in the cytoplasm of pluriblast cells suggests that this transcriptional regulator participates in allocating cells to the trophoblast lineage, as it does in mouse. Interestingly, in both mouse and opossum embryos, expression of the pluripotency marker Oct4 persisted after Cdx2, which signals trophoblast specification, began to be expressed in trophoblast cells. This and the observation that Cdx2 is present in opossum embryos well before blastomere–zona adhesion even occurs suggests that the proteins studied may have other roles in early mammalian embryonic development.

Husbandry of Monodelphis domestica in the study of mammalian embryogenesis

Monodelphis domestica, commonly called the laboratory opossum, is a useful laboratory animal for studying marsupial embryogenesis and mammalian development. Females breed year-round and the animals can be sustainably bred indoors. The authors draw on their own laboratorys experience to supplement previously published research on laboratory opossums. They describe a breeding protocol that reliably produces timed-pregnant M. domestica. Additionally, the authors discuss general laboratory opossum husbandry techniques and describe how to collect, handle and culture embryos.

Early pregnancy factor in marsupials

Maternal recognition of pregnancy in marsupials occurs in more subtle ways than it does in eutherians. For instance, unlike in eutherians, the plasma progesterone profiles of pregnant and non-pregnant animals are similar during the luteal phase. It is typically during the brief luteal phase that both gestation and parturition occur in marsupials. Yet histological and physiological changes have been documented between gravid and non-gravid uteri in certain monovular marsupials and between pregnant and non-pregnant animals in polyovular marsupials. Early pregnancy factor (EPF), a 10.8-kDa serum protein known to be homologous to chaperonin 10, is associated with maternal immunosuppression, embryonic development and pregnancy in eutherian mammals. It has been reported in two Australian marsupials: the dasyurid Sminthopsis macroura and the phalangerid Trichosurus vulpecula. This paper documents its occurrence in the New World didelphid Monodelphis domestica. EPF is detectable by rosette inhibition assay in the peripheral circulation of pregnant but not of non-pregnant or pseudopregnant animals. Our work focuses on the embryo–maternal signalling role of EPF during pregnancy. Because progesterone-driven changes are similar in pregnant and non-pregnant marsupials, these animals are an excellent laboratory model in which to investigate the role of EPF in orchestrating the physiological changes necessary to sustain pregnancy.

Expression analysis of Cdx2 and Pou5f1 in a marsupial, the stripe‐faced dunnart, during early development

The first lineage allocation during mouse development forms the trophectoderm and inner cell mass, in which Cdx2 and Pou5f1 display reciprocal expression. Yet Cdx2 is not required for trophectoderm specification in other mammals, such as the human, cow, pig, or in two marsupials, the tammar and opossum. The role of Cdx2 and Pou5f1 in the first lineage allocation of Sminthopsis macroura, the stripe‐faced dunnart, is unknown. In this study, expression of Cdx2 and Pou5f1 during oogenesis, development from cleavage to blastocyst stages, and in the allocation of the first three lineages was analyzed for this dunnart. Cdx2 mRNA was present in late antral‐stage oocytes, but not present again until Day 5.5. Pou5f1 mRNA was present from primary follicles to zygotes, and then expression resumed starting at the early unilaminar blastocyst stage. All cleavage stages and the pluriblast and trophoblast cells co‐expressed CDX2 and POU5F1 proteins, which persisted until early stages of hypoblast formation. Hypoblast cells also show co‐localisation of POU5F1 and CDX2 once they were allocated, and this persisted during their division and migration. Our studies suggest that CDX2, and possibly POU5F1, are maternal proteins, and that the first lineage to differentiate is the trophoblast, which differentiates to trophectoderm after shell loss one day before implantation. In the stripe‐faced dunnart, cleavage cells, as well as trophoblast and pluriblast cells, are polarized, suggesting the continued presence of CDX2 in both lineages until late blastocyst stages may play a role in the formation and maintenance of polarity. Mol. Reprod. Dev. 83: 108–123, 2016.