Patterning of the dorsal to ventral axis of the developing limb bud is triggered by the action of an ectodermal centre that resides on the dorsal surface. It is influenced by the wingless gene,wnt 7a, that is only expressed dorsally. Inactivation of this signalling pathway prevents the dorsal differentiation of the underlying mesoderm and two ventral pads result on either side of the mouse limb bud model. Wingless is a transcription factor that influences the gene Lmx-1.
It is likely that a diffusable morphogen influences patterning by determining the expression of Hox genes. For example, the homeobox-containing gene engrailed-1 is only expressed in ventral ectoderm.
BMP protein, likely to have a role in AP patterning, may also be involved with patterning in a dorso-ventral axis.
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