The role of murine cell surface galactosyltransferase in trophoblast: laminin interactions in vitro.

Implantation of the mouse embryo involves the invasion of the secondary trophoblast giant cells of the ectoplacental cone (EPC) into the uterine decidua. The mechanisms of this event are poorly understood. The putative substrate molecules found in the decidua which could support trophoblast invasion include laminin, fibronectin, and collagen type IV. EPCs dissected from Day 7.5 embryos were cultured on all three matrices. Galactosyltransferase (GalTase) was localized by immunolabeling on trophoblast cell surfaces when grown on laminin but not the other matrices. Perturbations of the enzyme:substrate complex with alpha-lactalbumin, uridine diphosphogalactose, anti-GalTase, and pregalactosylation of the matrix did not affect rates of EPC attachment. However, decreased rates of migration or altered morphologies of spreading cells were observed. Laminin, and not fibronectin or collagen type IV, could be galactosylated with both exogenous GalTase or EPC outgrowths. Digests of galactosylated laminin produced a glycoconjugate substrate with a molecular weight of less than 10K. The results suggest that invasive secondary trophoblast cells possess a GalTase-mediated migration system that is functional on laminin.