The CD44 protein family: Roles in embryogenesis and tumor progression

Members of the CD44 protein family are engaged in various physiological and pathological processes such as lymphocyte activation, lymphocytes homing, wound healing, delayed type hypersensitivity, apoptosis, tumor progression and limb development. Here we summarize observations which lead to a molecu lar understanding of the function of CD44 in some of these physiological pr ocesses. The most striking function for a CD44 variant protein is its prese ntation of growth factors to high affinity receptors on mesenchymal cells i n the developing limb. Furthermore we summarize the experiments that allowe d the identification of CD44 variant exon encoded sequences which account f or differentiation-specific and inducible splice regulation.