Fig. 5. Bts1 is sufficient to induce pax2.1 expression in the anterior neural plate. pax2.1 (A-D) or pax2.1 and gsc (E,F) expression revealed by whole-mount in situ hybridization (blue staining) at the tail bud stage on embryos injected with (A,B,D-F) wild-type bts1 RNA, or (C) mutant bts1C->T RNAs, as indicated (bottom left of each panel). (A-C) High magnifications of the MHD in flat-mounted embryos, anterior towards the top. (E) A whole-mount view, anterior towards the left. (D,F) Sections of the embryos in A,E (respectively) at the levels indicated, anterior towards the left. The red arrows in E,F point to gsc expression, and the broken line in F delimits the anterior mesendoderm/neural plate border. All injections were made into in one central blastomere of the 16-cell embryo, leading to a mosaic distribution of the injected RNA in the presumptive neural plate (see expression of the ß-galactosidase tracer (brown nuclei) and in particular D,F). Misexpression of bts1 induces ectopic pax2.1 expression (black arrows in A,B,E, black bars in D,F) anterior to the MHD (endogenous pax2.1 expression is indicated by the white arrowheads or white bars), in broad patches (A,D-F) or in scattered cells (B). Mutant bts1 RNAs (C, and data not shown) have no effect.
