Fig. 3. Abnormal development of the hindbrain- and the MHB primordium in spg mutants. (A-D) krox20 is not properly initiated in r3 (B,D) and r5 (D); in spghi349 mutant embryos, krox20 staining often fails to fuse at the midline in mutant embryos (D). (E) pax6 is expressed within the forebrain and the hindbrain, but spared at the MHB in wild-type embryos. (F) The forebrain expression domain of pax6 invades into the prospective MHB region (arrow). (G) pax2.1 expression is initiated between 80 and 90% of epiboly in wild-type embryos at the MHB. (H) In spghi349 mutant embryos, pax2.1 is downregulated from its onset of expression at the MHB.