Fig. 6. Distribution of SMCs in yolk sacs. Hand1 is required for the SMC in yolk sacs to migrate from the mesoderm and surround the endothelial tubes of the developing vasculature. Sections of yolk sacs from 8.5 dpc Hand1^ß-gal/+ (A,D,G,J) and 9.5 dpc Hand1^{ß-gal/ß-gal} mice (B,C,E,F,H,I,K,L) were stained with anti-ß-gal antibody to visualize Hand1 expression (A-C) and anti-SMA antibody to visualize SMCs (D-F). SMCs were located in the peri-endothelial and peri-endodermal cells in Hand1^ß-gal/+ yolk sac (D). In Hand1^{ß-gal/ß-gal} yolk sacs, SMCs were rarely found in regions surrounding the developing vasculature (E). (G-I) Merged images of A-F. (J-L) Phase contrast images of A-I. Instead, SMCs were scattered in clusters in extra-embryonic mesoderm of Hand1^{ß-gal/ß-gal} yolk sacs (F). end, extra-embryonic endoderm; mes, extra-embryonic mesoderm. Asterisk indicates blood vessel. C,F,I,L are images of Hand1^{ß-gal/ß-gal} extra-embryonic mesoderm only.