Fig. 1. Expression of integrin subunits in EBs and early mouse embryos. (A) Cell lysates of 5-day-old normal EBs were subjected to western blot analysis for integrin subunits β1, 1, 2, 3, 5, 6, v, β3, β4 and β5. β1, 5, 6 and v were expressed in differentiated EBs. (B) Normal EBs at different developing stages (days 2-7) were immunostained for integrins 5, 6 and v, and for the BM components fibronectin and laminin. The insets are 2x magnifications of the boxed regions. en, endoderm; epi, epiblast; cv, cavitation. (C) Co-immunoprecipitation showed that integrin β1 formed a complex with the integrin 5, 6 and v subunits. (D) Immunofluorescence analysis of E6.5 mouse embryos showed that integrin 5 was mainly expressed in the endoderm, whereas 6 was mainly expressed in the epiblast, and both were recruited to the embryonic BM (EBM) zone (arrows), as revealed by fibronectin and nidogen immunostaining. Integrin v was not detected at the cell-EBM adhesion but at the trophoblast–Reichert's-membrane (RM) interface (arrowheads).