Fig. 3. Expression of laminin chains in normal and mutant early postimplantation embryos. (A-G) Arrowheads indicate the embryonic basement membrane and the arrow indicates RM. (A) At E5.5, laminin 1 was detected in the embryonic basement membrane and in RM. (B) At E6.5, laminin 5 (red) is detected primarily in the embryonic basement membrane, though some is apparent in RM at the ectoplacental pole (asterisks). Laminin 1 (green) is abundant in RM, but its presence in the embryonic basement membrane is obscured by the 5 staining. (C,E-G) At E7.5 in wild type, laminin 1 (green) is present in both the embryonic basement membrane and in RM, but laminin 5 (red) appears confined primarily to the embryonic basement membrane. (D) This embryo is Lama5^-/-, demonstrating the specificity of the 5 antibody. Note staining for 5 in the surrounding maternal tissue. (F) Note the absence of 5 in RM. (G) Nuclei (blue) are visible in the merged images. (H-J) X-gal staining of sections of Lama1^+/- and Lama1^-/- embryos, as indicated. Cells of the PE at the periphery of the normal embryos stain blue (H,I). In the mutant, the cells stain blue but are found in a cluster next to the small embryo (asterisk in J) owing to failure to migrate. Scale bar in A: 100 µm for A-D,H-J; 33.3 µm for E-G.