Integrins constitute a family of heterodimeric transmembrane glycoproteins involved in cell-substratum or cell-cell interactions. At least 16 alpha and 8 beta subunits have been identified, that may exhibit alternative splicing. Recently, a new muscle-specific splice variant of the B1 subunit has been identified, B1D. B1D is developmentally up-regulated during differentiation of myoblasts and is the most prominent B1 isoform in muscle tissue. Aim of this project is to specify the role of B1D in myogenesis and in muscular physiology. The main objectives include the study of the function of B1D in skeletal and cardiac muscle formation by gene targeting experiments as well as the assessment of its role in myoblast differentiation using an in vitro model. Insights into cell adhesion and integrin-mediated signal transduction will also be gained. Noteworthy, a novel gene targeting approach based on the Cre-loxP system will be used to generate splice variant specific knock-out mice.