Fig. 1. Mesoderm defects in chato embryos. Wild-type (wt) (A,C,E,G) and chato mutant (B,D,F,H) mouse embryos were assayed by in situ hybridization with markers expressed in head mesenchyme/lateral plate mesoderm/somitic mesoderm (Twist1; A,B, dorsal and ventral views, respectively), somites (Meox1; E,F, ventrolateral views) and cardiac mesoderm (Nkx2.5; G,H, ventral views). Staining for β-galactosidase activity from a Nodal-lacZ reporter labeled lateral plate mesoderm and node of wild-type (C) and chato mutant (D) embryos (lateral views). Thirty-three percent of chato mutants (n=184) had condensed somites that appeared narrow and laterally extended (F). In 52% of chato embryos (n=184), somites were not clearly discernible morphologically, but somite markers Twist1 and Meox1 marked some imperfectly shaped somites. Only 15% of chato mutants showed normal somites. Arrowheads in A,B point to head mesenchyme. Brackets in C,D highlight the different width of the lateral plate mesoderm in wild-type and chato mutant embryos. Brackets in E,F highlight the different width of the somites. Arrowheads in H mark the cardiac mesoderm in chato mutants. LPM, lateral plate mesoderm; som, somites.