Fig. 10. Sim1 and Sim2 repress Rig-1/Robo3 expression in the developing mammillary body. (A-T) Coronal sections through the MB of E12.5 Sim1^+/-;Sim2^+/+ and Sim1^-/-;Sim2^-/- embryos were hybridized either with a Slit1 (A-D), Slit2 (E-H), Robo1 (I-L), Rig-1/Robo3 (M-P) or Sim1 (Q-T) probe. Sections correspond either to the anterior or posterior aspect of the MB, as indicated. The sections hybridized with the Rig-1/Robo3 probe (M-P) are adjacent to those hybridized with the Sim1 probe (Q-T). Expression of Slit1, Slit2 and Robo1 is similar in Sim1^+/-;Sim2^+/+ and Sim1^-/-;Sim2^-/- embryos. In the anterior MB of Sim1^+/-;Sim2^+/+ embryos, Rig-1/Robo3 is expressed in a narrow region that includes a medial domain (yellow arrowhead) that is contained within the dorsal aspect of the MB Sim1 expression domain (M,Q). In Sim1^-/-;Sim2^-/- embryos, Rig-1/Robo3 expression in the prospective MB (arrow) occupies a larger area extending ventrally and laterally (N,R). Rig-1/Robo3 expression in the region dorsal to the MB (blue arrowhead) is decreased in Sim1^-/-;Sim2^-/- embryos (M,N). In the posterior MB, Rig-1/Robo3 expression is upregulated in Sim1^-/-;Sim2^-/- embryos (arrow) (O,P). (U-B') Coronal sections through the MB of E11.5 Sim1^+/-;Sim2^+/+ and Sim1^-/-;Sim2^-/- embryos were hybridized either with a Rig-1/Robo3 (U-X) or a Sim1 (Y-B') probe. Sections correspond either to the anterior or posterior aspect of the MB, as indicated. The sections hybridized with the Rig-1/Robo3 probe (U-X) are adjacent to those hybridized with the Sim1 probe (Y-B'). (U,V) Rig-1/Robo3 is ectopically expressed (V) in the MB (arrows). (W,X) Asterisks indicate a second region in which Rig-1/Robo3 expression is upregulated (X).