FIG. 3.

X-Gal staining of Six4 heterozygous mutant embryos showing spatiotemporally regulated expression of Six4 in somites and myotomes (SO), cranial and dorsal root ganglia (V to XI) (DRG), sensory placodes (otic [OP] and nasal [NP]), and some other restricted areas. (A) At E8.5, Six4 expression commences in the surface ectoderm of the head region (HE) and presomitic mesoderm (PSM). (B) At E9.5, note the expression of Six4 in OP, NP, SO, branchial arches (BA), and cranial ganglia (CG). (C) At E10.5, Six4 expression is evident also in DRG. (D) At E11.5, Six4 is expressed also in mesenchymal tissues of fore- (FL) and hindlimb (HL) buds at the posterior margin. (E) At E13.5, Six4 expression in digits becomes evident. (F) The embryo at E10.5 was cleared with benzylbenzoate-benzylalcohol after staining. Note the staining of cranial ganglia V and VII-XI, DRG, and otic vesicles (OV). (G) X-Gal staining of a transverse section of an embryo at E9.5 at the hindlimb level shows strong staining in dermamyotomes (DM) and weak staining at sclerotomes (SC) of somites. (H) In situ hybridization of a sagittal section of an embryo (Jcl:ICR strain) at E11.5, showing Six4 expression at cranial ganglia (VII and VIII) and OV. As analyzed, in situ hybridization to Six4 transcripts and X-Gal staining of heterozygotes showed essentially the same pattern. One of the typical hybridization results are shown.