Subunits of laminin are differentially synthesized in mouse eggs and early embryos

Synthesis of laminin by mouse preimplantation embryos was examined by specific immunoprecipitation of [35S]methionine-labeled cell lysates. The three polypeptide subunits of laminin, A, B1, and B2, are not necessarily synchronously expressed during development. Oocytes and eggs synthesize only one immunoprecipitable polypeptide, which comigrates with the intracellular B1 chains made by PYS cells and contains N-linked oligosaccharide residues which are sensitive to endo-beta-N-acetylglucosaminidase H. From the 4- to 8-cell stage, only B1 and B2 polypeptides are synthesized, whereas from the 16-cell stage onwards all three laminin polypeptides are made.