Sox7 expression in gastrulating embryos. (A) Gene expression analysis performed by RT-PCR on pools of wt embryos at the indicated stage of development. (B) Pictures of E7.5 embryo wild-type (WT) or transgenic for the Sox7-GFP transgene. Arrows indicate the mesodermal masses. Merge picture of GFP and brightfield (×10 magnification). (C) Stage-matched pool of embryos from WT or Sox7-GFP litters stained for Flk1 and CD41 expression. 4S indicates 4 somites. All data are representative of at least 3 independent experiments.