LIMB MORPHOGENESIS - CONNECTIONS BETWEEN PATTERNING AND GROWTH

Limb development is a complex process involving precise control of bot h patterning and growth, Great strides have been made in understanding limb morphogenesis and identifying essential patterning genes in Dros ophila, Differential expression of these genes divides the future limb into territories, which will give rise to different regions of the ad ult appendage, Recent analyses have defined the role of territorial bo undaries as organizers of both patterning and growth, highlighting the connection between these two processes, The organizing activity of te rritorial boundaries seems to be mediated through the activity of two locally produced morphogens: Wingless and Decapentaplegic. We propose a model in which these two molecules, distributed in a graded fashion, act in synergy to promote growth of the entire appendage, We also sug gest the existence of growth inhibitors that counteract the action of Wingless and Decapentaplegic; by opposing the gradient of these growth factors, the inhibitors guide the near uniform proliferation that sha pes the imaginal discs from which the adult appendages are formed in D rosophila.