13-P058 The mitogen activated protein kinase p38 amplifies Nodal signalling in anterior/posterior axis development in the mouse embryo

In the mouse, however, it has been demonstrated that the two most posterior of the five digits are derived entirely from the polarizing region by proliferation without the requirement of Shh diffusion. To understand the contribution and significance that polarizing region cell proliferation has in forming different digit patterns, we grafted polarizing regions from a transgenic chicken line stably expressing Green Fluorescent Protein (GFP) into normal wing buds (three digits), or leg buds (four digits). We will describe how these fate-maps behave when either Shh signalling is dampened, or proliferation is inhibited. We will present a model outlining our findings, highlighting the evolutionary implications.