Fig. 1. Wnt1 promotes proliferation and inhibits differentiation. (a-c) Transfection of forelimb level chick spinal neural precursors by in ovo electroporation with a plasmid containing an internal ribosome entry sequence followed by nuclear GFP (a), gives rapid, ubiquitous, unilateral expression with cellular resolution and does not perturb normal development (b,c). (d,e) Embryos transfected with Wnt1 show an increase in BrdU incorporation (4 hour labeling) at ventral levels (marked by bracket) and a decrease in post-mitotic neurons marked with N-tubulin. (f-h) Rates of proliferation and differentiation were quantitated using BrdU cumulative labeling and N-tubulin staining in stage 22 embryos in both the transfected (green) and untransfected sides (red). Ectopic Wnt1 expression increased the BrdU labeling index to a progressively greater degree ventrally (f). BrdU cumulative labeling shows that ectopic Wnt1 increases both the proliferation rate and the fraction of cells in S-phase in the ventral three fifths of the ventricular zone (g). Wnt1 transfected precursors have a 55% reduction in the rate of differentiation (h).
