Fig. 7. Graded Blimp1 activities required for germ cell specification and development of the cardiovascular system, forelimbs and vibrissae. (A,B) Homozygous Blimp1^gfp/gfp embryos display cardiovascular defects including PTA and VSD. Fast Red alkaline phosphatase staining of PGCs in the dorsal hindgut of wild-type (C), gfp/+ (D) and gfp/gfp (E) E9.5 embryos. Decreased numbers of PGCs are specified in gfp/+ embryos and homozygous mutants entirely lack PGCs. (F-H) Homozygous gfp/gfp forelimbs contain a rudimentary ulna and four digits (G). Heterozygous gfp/- embryos with further reduced Blimp1 activity entirely lack the ulna and are missing the posterior two digits. (I,J) Induction of the sensory vibrissae is relatively Blimp1 independent because vibrissae induction is unperturbed (arrows), and ectodermal placode induction and invagination occurs normally in gfp/gfp homozygous embryos (J). Blimp1 expression in gfp/- embryos is sufficient for coalescence of the prospective DP cells, but these fail to induce overlying ectodermal placodes (K). DC, dermal condensates; LV, left ventricle; PTA, persistent truncus arteriosus; R, radius; RV, right ventricle; U, ulna; VSD, ventricular septal defect.