Conditional loss of MT1-MMP in an MT2-MMP deficient background after LA formation is compatible with development to term. (A) Whole mount preparation of a Cre− embryo treated with TMX after the LA was formed (from E12.5 to 16.5). (B) Cre+ littermate with identical gross appearance despite MT1-MMP and MT2-MMP-deficiency after TMX treatment. (C) Relative expression level of MT1-MMP mRNA evaluated by real-time PCR on embryonic tissue (from A and B) demonstrates complete ablation of MT1-MMP after treatment with TMX in the presence of Cre. (D-E) H&E–stained cross-sections of the placentas corresponding to the embryos shown in panels A and B, respectively. Note the abundant vascularization of both placental LAs despite the conditional loss of both MT1-MMP and MT2-MMP in (E). Compare with the control placenta after formation of the LA in panel D. Scale bars: (A-B) 1 mm; (D-E) 200 μm.