The Influence of Extracellular Matrix Components on the Proliferation and Migration of Inner Cell Mass-Derived Parietal Endodermal Cells1

Reichert’s membrane is a basement membrane deposited on the inner surfaces of rat and mouse trophectodermal (TE) cells beginning at the blastocyst stage of embryonic development that may play a role in the migration of the parietal endodermal (PE) cells to form an inner lining to the TE. The abilities of various glycoproteins present in Reichert’s membrane to support PE cell migration and replication in vitro were examined by isolating inner cell masses (ICMs) from Day 5 rat blastocysts (Day 1 = day of vaginal plug) and culturing them (24–72 h) either on surfaces that had been precoated with collagen IV, fibronectin, or laminin or on thin (1–2-mm) gels of Matrigel (a tumor cell-derived basement membrane preparation) or type I collagen. Time-dependent changes in the area occupied by each ICM on the culture surface and the number of migrating cells per ICM were quantified by morphometric analysis. Type IV collagen, the basement membrane-specific collagen, supported ICM attachment and the outward migration (overall increase of approx. 60-fold in mean ICM area occupied on the culture surface) and proliferation (cell doublings following every 24 h of culture) of laminin-containing PE-like cells. These effects were not altered by the inclusion of exogenous fibronectin or laminin in the culture medium. Collagen IV coating concentrations as low as 0.16 μg/ml supported PE cell attachment and migration, and maximal responses were seen with a coating concentration of 0.63 μg/ml. Fibronectin or laminin coatings also supported cell migration and proliferation, although the translocation (at 72 h) and replication (at 48 and 72 h) responses on laminin were lower than those observed on either fibronectin or collagen IV. On the other hand, type I collagen gels only minimally supported PB cell translocation and proliferation, and no cell migration was observed when cells were cultured on Matrigel. Reichert’s membrane is a complex mixture of numerous extracellular matrix glycoproteins. These findings demonstrate that three key components of this basement membrane-collagen IV, fibronectin and laminin-support the in vitro migration and proliferation of PE cells, the first embryonic cell lineage to be established after blastocyst formation.