We are studying the inter-relationship between FGF and BMP signaling. Limb development is ideal for such studies because of the wealth of information describing the genetic pathways and signaling molecules that pattern the three axis of the limb. Current models of limb development suggest that BMP signaling plays a role in controlling the normal cell death that occurs in mesenchymal interdigit cells, sculpting the final digit pattern, but the exact role of BMPS in this process are unknown. By inactivating the Bmp receptor gene, Bmpr1a specifically in the limb bud ectoderm, we have produced genetic evidence for a model in which the surface ectoderm must receive a BMP signal, resulting in down regulation of FGFs which in turn induces apoptosis of the underlying mesenchyme. Thus both BMPs and FGF cooperate to control the essential cell function of programmed cell death. We are extending these studies by studying the role of BMP and FGF signaling in various aspects of limb development using mouse lines that express Cre in specific region of the developing limb.