Uterine Receptivity in Merriam's Kangaroo Rat (Dipodomys merriami).

The uterine surface undergoes significant remodeling, termed the "plasma membrane transformation," during pregnancy to allow for implantation of the blastocyst and formation of the placenta in viviparous amniote vertebrates. Unlike other species within the superorder Euarchontoglires, which have a hemochorial (highly invasive) placenta, kangaroo rats (Dipodomys spp.) exhibit a less invasive endotheliochorial placenta. We characterized the changes that occur to membrane molecules and the cellular ultrastructure of the uterine epithelium during early pregnancy in Merriam's kangaroo rat, Dipodomys merriami using electron microscopy and immunofluorescence microscopy. Epithelial cadherin (E-cadherin) is an adhesion protein that forms the adherens junction and is localized to the lateral plasma membrane of uterine epithelium during the nonreproductive state but localizes nonspecifically in the uterine epithelium immediately preceding implantation. Desmosomes are a type of cadherin that form junctional complexes along the lateral plasma membrane of epithelium. Dsg-2, a marker for desmosomes, is localized along the lateral plasma membrane in non-pregnant animals but redistributes to the apical region of the lateral plasma membrane during early pregnancy. The shift in desmosome and cadherin distribution before implantation suggests that there is a reduction in lateral adhesion between epithelial cells to allow for invasion by the blastocyst. Surprisingly, although Kangaroo rats form a less invasive placenta, these same changes occur during pregnancy in species with highly invasive placentation, such as the laboratory rat and human. These commonalities suggest that it is not through the retention of lateral adhesion that the blastocyst is prevented from further invasion in this rodent species. Anat Rec, 301:1928-1935, 2018. © 2018 Wiley Periodicals, Inc.