Expression of Rarb is seen in the mesonephros (the embryonic kidney derived from the intermediate mesoderm), and eventually appears in the metanephros or definitive kidney (Figure 6F,G). Expression is found in the kidney stromal mesenchyme, rather than in cells of the developing nephrons [Mendelsohn et al., 1999], and it is the Rarb2 isoform which is predominantly (or exclusively) expressed [Mollard et al., 2000]. Rara is also expressed throughout the developing kidney, and Rara/Rarb2 compound mutants display abnormal kidney development [Batourina et al., 2001; Mendelsohn et al., 1999]. Both Rarb isoforms are also expressed according to distinct spatial domains in the mesenchyme surrounding the urogenital sinus, ureters and developing genital tract. Additional abnormalities in Rara/Rarb2 mutant mice include an incorrect insertion of the uterers into the developing bladder, as well as agenesis of the Mullerian ducts (precursors of the oviduct and uterus) [Batourina et al., 2001; Mendelsohn et al., 1994b].
