Tenm4m1/m1mutant embryos arrest at the gastrulation stage and fail to develop a mesoderm. Wildtype and Tenm4m1/m1 mutant embryos at E6.5 – 8.5 (A-F). Tenm4m1/m1mutant embryos (D) are similar to wildtype littermates at E6.5 (A). E7.5 Tenm4m1/m1mutant embryos (E) have a poorly defined extraembryonic region. E8.5 wild-type embryos (C) start organogenesis, whereas the Tenm4m1/m1mutant embryos (F) do not develop or grow. Histological paraffin sections were prepared from wildtype littermates (G-I) and Tenm4m1/m1mutant embryos (J-L), and stained with hematoxylin and eosin. Sagittal sections of heterozygote and Tenm4m1/m1embryos at days E6.5 (G and J), E7.5 (H and K) and E8.5 (I and L). Thickness of all sections is 7 mm. Epiblast (e), ectoplacental cone (ec), heart (h), head fold (hf), mesoderm (m), and visceral endoderm (ve). Bar 100 μm. PCR genotyping was used to identify the mutant classes. Developmental stages and genotypes are indicated at the top and left of the panels, respectively.