Fig. 1. Xsix3 promotes cell proliferation in the neural plate. (A-D) Transverse sections of stage 13 embryos injected with either Xsix3 (A,C) or VP16-Xsix3 (B,D), processed simultaneously for BrdU incorporation (brown nuclear staining), and Zic2 (A,C, blue staining) or lacZ (B,D, red staining) expression. Sections are at the level of the anterior (A,B) or posterior neural plate (C,D). ANP, anterior neural plate; PNP, posterior neural plate. (E,F) The average number of BrdU-positive cells per section in either the control side (magenta) or the side injected with Xsix3 (blue) or VP16-Xsix3 (green). Error bars indicate s.e.m. (G) Double whole-mount in situ hybridization of a stage 13 embryo shows that the Xsix3 (magenta) and Xbf1 (purple) expression domains overlap. (H-J) Stage 13 (H,I) and stage 14 (J) embryos injected with Xsix3 display expansion of the Xbf1 (H), Xrx1 (I) and cyclinD1 (J) expression domains. White brackets indicate the anterior expression domain of cyclinD1 in the control (right) and injected (left) side. (K,L) Xsix3 overexpression represses p27Xic1 both in the anterior, trigeminal ganglion (K, arrow) and in its posterior expression domain (L, arrow) in stage 13 embryos. (G-K) Frontal views, dorsal towards the top; (L) dorsal view, anterior towards the bottom. Red staining represents expression of a co-injected lacZ lineage tracer. The injected side of the embryos (to the left of vertical bars or dotted lines representing the midline) is indicated (inj).