Fig. 7. Ectopic expression of porcupine in the chick neural tube steepens the Wnt1/Wnt3a proliferation gradient. mPorcD was transfected into the neural tube by electroporation. GFP-positive embryos were harvested for analysis 48 hours post-electroporation. Embryos were fixed, cryosectioned and immunostained with anti-phosphohistone H3 (red), which marks cells in late G2/M phase. The neural tube was divided into quintiles for quantitation of proliferation, as illustrated in schematic to left. The red dots represent mitotic cells in each quintile. The proliferation index for the control and experimental sides of the neural tube was determined and graphed for each quintile. A total of 43 sections derived from three different embryos were analyzed. Error bars indicate standard error.