The limb bud is a system of paradigmatic value to analyze vertebrate organogenesis. One major question is when and how the chondrogenic progenitors of the limb skeleton are determined. Recent studies suggest that digit identities are only fixed during advanced autopod development by BMP signal transduction. Here, I propose an in-depth analysis of the underlying signaling systems using mouse limb buds to gain insight into the requirement of Smad4-dependent and independent BMP signaling for chondrogenesis. Furthermore, the relevance of these findings to engineering cartilage and bone from adult mesenchymal stem cells will also be investigated, which is of significant biomedical relevance towards efforts to improve human health.Aim 1. BMP signaling in determination of digit identities and chondrogenesis. These processes are disrupted in Smad4 deficient mouse limb buds. Therefore, I will study the cellular and molecular alterations of Smad4-/- in comparison to other mutant and wild-type limb bud mesenchymal cells.Aim 2. Identification and functional analysis of the molecular networks controlling Sox9 expressing digit progenitors. The transcriptomes of digit and interdigit mesenchymal regions of wild-type and mutant autopods will be analyzed. Such identified candidate regulators will be investigated further to identify the networks governing determination of Sox9 expressing digit progenitor cells.Aim 3. The potential relevance for adult skeletal repair and engineering of cartilage and bone tissue from mesenchymal stem cells. Comparative molecular and functional analysis to provide insights into the similarities of limb bud and adult mesenchymal stem cells.