The essential roles of the small GTPase Rac1 in limb development

Vertebrate limbs develop through complicated interactions between various types of cells of the ectoderm and mesenchyme, which facilitate the proper steps of growth and formation by cell proliferation, differentiation, and apoptosis. These processes are regulated by several signaling proteins such as Fgf, Bmp, and Wnt. Recently, several types of Rac1 conditional knockout mice were created, and Rac1 was observed to play essential roles in each of the developing limb tissues. Mice with genetic deletion of Rac1 in the chondrocytes, the limb bud ectoderm, or the limb bud mesenchyme exhibit dwarfism with short limbs, severe truncations of limbs, or syndactyly with short limbs, respectively. Analyses of these mice demonstrated that Rac1 regulates limb development by controlling many kinds of gene expression and various cellular functions.