Alterations to the basal attachment points between the epithelium of the uterus and the underlying tissue in early pregnancy affect how easily the epithelium can be invaded by the implanting embryo. Attachment points- focal adhesions- disassemble to facilitate highly invasive implantation in rats, but species with less invasive implantation, including marsupials, may require different basal alterations for successful pregnancy. Here we used immunofluorescence microscopy and Western blotting to conduct the first study of basal plasma membrane dynamics in the uterus during marsupial pregnancy. We describe localisation patterns of two key anchoring molecules, talin and paxillin, throughout pregnancy in the fat-tailed dunnart (Sminthopsis crassicaudata; Dasyuridae). Basal staining of both molecules occurs in early pregnancy, as it does in the rat. However, unlike rats, there is strong basal localisation of talin and paxillin just before implantation in S. crassicaudata, indicating that focal adhesions do not disassemble during pregnancy in this species, and that molecular reinforcement of the epithelium may be a maternal strategy to regulate invasion. Additionally, talin and paxillin do not co-localise at all stages of pregnancy as they do in the rat. Different localisation patterns among mammalian species demonstrate that not all early pregnancy changes are ubiquitous in mammalian pregnancy, as changes to the basal plasma membrane of the epithelium, in particular, may instead be dependent on mode of implantation. Anat Rec, 300:1150-1159, 2017. © 2016 Wiley Periodicals, Inc.

Amniotes (birds, reptiles and mammals) exhibit a remarkable range of reproductive strategies. The transition from oviparity (egg-bj/ing) to viviparity (live birth) has occurred independently multiple times in squamate reptiles (snakes and lizards) and once in therian mammals (placental mammals and marsupials) and requires many changes to the uterus to allow the embryo to develop inside the mother. An important step in this transition is the evolution of a placenta. Formation of a placenta in early pregnancy requires substantial remodelling of the surface of the uterus, termed the plasma membrane transformation. Similar cellular changes occur in both placental mammals and live-bearing squamate reptiles which surest this phenomenon plays an important role in the evolution of amniote viviparity.Marsupials are ideally placed to test theories of the generality and importance of the plasma membrane transformation of the uterus. Similar morphological changes also occur in a marsupial species {Sminthopsis crasskaudata; Dasyuridae), su^esting these changes are ubiquitous in amniote pregnancy, but remodelling appears to be underpinned by different molecular changes in each group. This study demonstrates that not all uterine changes are common across vertebrate Lineages. Thus, the transition from egg-laying to live birth may involve flexible molecular recruitment as common molecules do not play the same roles in pregnancy in different Mve bearing groups. This study highlights the necessity of including marsupials as a separate mammalian group in comparative studies, and the valuable and novel contribution marsupials can make to evolutionary theories. BoschInstitute Advanced Microscopy Facikty, University of Sydney. Animals were used according to University Animal Ethics protocol no. K22/ 5-2012/ 1 / 5764.