Getting a handle on embryo limb development: Molecular interactions driving limb outgrowth and patterning.

Development of the vertebrate embryo involves multiple segmentation processes to generate a functional, articulated organism. Cell proliferation, differentiation and patterning involve spatially and temporally regulated gene expression and signal transduction mechanisms. The developing vertebrate limb is an excellent model to study such fine-tuned regulations, whereby cells proliferate and are differentially sculptured along the proximal-distal, anterior-posterior and dorsal-ventral axes to form a functional limb. Complementary experimental approaches in different organisms have enhanced our knowledge on the molecular events underlying limb development. Herein, we summarize the current knowledge of the main signaling mechanisms governing vertebrate limb initiation, outgrowth, specification of limb segments and termination.