The progenitors of the ENS fail to colonize the colon of miRet51/miRet51 embryos. In situ hybridization with riboprobes specific for EdnrB (a–f) and Phox2B (g–l) mRNAs on serial sections of small intestine (a–c,g–i) and colon (d–f,j–l) of +/+ (a,d,g,j), miRet9/miRet9 (b,e,h,k) and miRet51/miRet51 (c,f,j,l) E13.5 embryos. mp, Myenteric plexus. For all genotypes n = 3.