Fig. 4. Regulation of D-type cyclins by Wnts. (a-d) cyclin D1 is expressed in a dorsal to ventral gradient. In situ hybridization at E8.5, E9.5 and E11.5 (a,b,c) shows cyclin D1 is expressed in neural precursors in a DV gradient. cyclin D1 is also transiently expressed in some differentiating neurons as marked by arrows in b and c. (d) Normalized quantitation of cyclin D1 expression levels shows that the gradient extends completely across the DV axis when the spinal cord is small and becomes more dorsally restricted as the spinal cord grows. (e-q) Sections of transfected embryos were first visualized for GFP (e,g,i,k,m,o,q) and then stained by in situ hybridization (f,h,j,l,n,p). Dominant active ß-catenin upregulates cyclin D1 and cyclin D2 (e-h). cyclin D1 can be upregulated at all dorsal-ventral levels but cyclin D2 can only be upregulated dorsally (upregulation marked by bracket). Dominant active ß-catenin does not upregulate the expression of the G2/M cyclins cyclin A1 (i,j) or cyclin B3 (k,l). Wnt1 upregulates cyclin D1 expression at ventral levels but not at dorsal levels (upregulation marked by bracket) (m,n). Dominant negative TCF4 downregulates cyclin D1 at all levels of high transfection efficiency as marked by bracket (o,p). Dominant negative cyclin D1 reduces precursor expansion (q).
