Dorsoventral patterning of the vertebrate limb: A process governed by multiple events

In this review, we detail recent studies which have led to the first molecular insights into dorsoventral vertebrate limb patterning. In keeping with classical experiments which defined ectodermal-mesodermal signaling as an important component of limb bud dorsoventral axis specification, the genes identified to date to be critically important for proper dorsoventral limb patterning include both ectodermally and mesodermally expressed cell:cell signaling molecules and transcription factors. A surprising complexity to dorsoventral vertebrate limb patterning has been revealed by gene targeting in the mouse and lineage tracing in the chick, with current models suggesting that the dorsoventral limb axis is specified by distinct mechanisms in the proximal versus distal limb.