Trophoblast are the earliest differentiated cells to emerge during mammalian ontogeny. Proper differentiation and maturation of trophoblast contributes to the fetal-maternal vascular interface of the mature placenta and is required for all subsequent stages of embryogenesis. Although lineage commitment and early differentiation of trophoblast have been investigated experimentally, molecular markers and regulatory mechanisms operating later in trophoblast development remain uncertain. We now report that E-selectin is expressed in a unique pattern in secondary trophoblast giant cells, trophoblast lining the central artery, and a subpopulation of labyrinthine trophoblast all located at the fetal-maternal interface of the murine placenta. These cells line vascular channels but express a unique profile of gene products not displayed by vascular endothelium. Placentae lacking E-selectin show increased trophoblast glycogen cells and fewer labyrinthine neutrophils compared with normal placentae, suggesting that recognition of E-selectin on trophoblast by counter-receptors on other cells contributes to placental development. Novel, distant first exons direct E-selectin expression in both murine and human placentae, suggesting that evolutionarily conserved and lineage-restricted transcriptional mechanisms regulate expression in homologous trophoblast populations in both species. These results define, at molecular and anatomic levels, a unique population of trophoblast located at the physiologically critical fetal-maternal vascular interface in mice. We also present initial functional characterization of E-selectin in placenta. These results support the general hypothesis that endothelial-leukocyte adhesion molecules performing specialized functions in adults may also function in development of human and murine hemochorial placentae.
Copyright 2000 Wiley-Liss, Inc.