Fig. 3. Only dorsal midline Wnts have mitogenic activity. (a,c) Wnt1 and Wnt3a have similar expression patterns in the dorsal midline. (b,d) Neural precursors transfected with Wnt1 or Wnt3a have increased BrdU labeling index (4 hour incorporation) and a decreased number of post-mitotic neurons. (e,g) Wnt3 and Wnt4 are expressed in broad dorsal domains. Wnt4 is also expressed in the floor plate (g). (i,k) Wnt7a and Wnt7b are expressed in broad ventral domains. (f,h,j,l) Neural precursors transfected with the non-dorsal midline Wnts, Wnt3, Wnt4, Wnt7a or Wnt7b, have normal BrdU incorporation and numbers of post-mitotic neurons. (m,n) The BrdU labeling index in the ventral three fifths of the VZ and the number of post-mitotic neurons were quantitated for these and other embryos. All sections were visualized for GFP to ensure good transfection before staining.