Current research on mechanisms of limb bud development, and challenges for the next decade.

The developmental mechanisms of limb buds have been studied in developmental biology as an excellent model of pattern formation. Chick embryos have contributed to the discovery of new principles in developmental biology, as it is easy to observe live embryos and manipulate embryonic tissues. Herein, I outline recent findings and future issues over the next decade regarding three themes, based on my research: limb positioning, proximal-distal limb elongation and digit identity determination. First, how hindlimb position is determined at the molecular level is described, with a focus on the transforming growth factor-β signaling molecule GDF11. Second, I explain how the cell population in the limb bud deforms with developmental progress, shaping the limb bud with elongation along the proximal-distal axis. Finally, I describe the developmental mechanisms that determine digit identity through the interdigits.