Fig. 2. The vascular network organizes itself independently of muscle. (A) Transverse sections of E9.5 forelimbs of Pax3^GFP/+ mouse embryos were incubated with the PECAM antibody (red) to visualize vascular cells. GFP (green) reveals the Pax3-expressing cells. DAPI staining (blue) visualizes the nuclei. (B,C) E13.5 forelimbs from Pax3^+/+ and Pax3^-/- mutant mice were cut transversally and then incubated with the PECAM antibody. (D,E) E13.5 hindlimbs of Pax3^+/+ and Pax3^-/- mutant mice were cut transversally and hybridized with the Hif2 probe and then incubated with the MF20 antibody. The asterisks show ventral muscles in control limbs (B,D) and the equivalent sites corresponding to the absent muscles in Pax3^-/- limbs (C,E). Both muscles and muscle-less sites are surrounded by the vasculature.