Fig. 4. Non-cell-autonomous effect of the Ret^- mutation on the colonisation of E8.5 by Ret⁺ ENS progenitors. Whole-mount X-Gal staining of E8.5+3+7 guts from Ret^+/- (A) and Ret^-/- (B) mouse embryos grafted with Ret⁺ cells from the intestine of E11.5 Rosa26bgeo embryos. Contrary to control gut (A), no β-gal⁺ cells were detected beyond the anterior foregut of Ret-deficient gut (B). Representative images of Ret^+/- (C) and Ret^-/- (D) E8.5+3 embryos grafted at E8.5 with Ret⁺ cells isolated from the intestine of E11.5 embryos. Grafted embryos (three homozygous mutant and 12 heterozygous or wild-type) were cultured for 3 days and then processed for β-gal histochemistry. Arrows in C and D point to β-geo⁺ cells in the foregut (stomach and duodenum anlage). st, stomach; mg, midgut.