LOCAL INHIBITORY-ACTION OF BMPS AND THEIR RELATIONSHIPS WITH ACTIVATORS IN FEATHER FORMATION - IMPLICATIONS FOR PERIODIC PATTERNING

The formation of periodic patterns is fundamental in biology. Theoreti cal models describing these phenomena have been proposed for feather p atterning; however, no molecular candidates have been identified. Here we show that the feather tract is initiated by a continuous stripe of Shh, Fgf-4, and Ptc expression in the epithelium, which then segregat es into discrete feather primordia that are more strongly Shh and Fgf- 4 positive. The primordia also become Bmp-2 and Bmp-4 positive. Bead-m ediated delivery of BMPs inhibits local feather formation in contrast with the activators, SHH and FGF-4, which induce feather formation. Bo th FGF-4 and SHH induce local expression of Bmp-4, while BMP-Q suppres ses local expression of both. FGF-4 also induces Shh. Based on these f indings, we propose a model that involves (1) homogeneously distribute d global activators that define the field, (2) a position-dependent ac tivator of competence that propagates across the field, and (3) local activators and inhibitors triggered in sites of individual primordia t hat act in a reaction-diffusion mechanism. A computer simulation model for feather pattern formation is also presented. (C) 1998 Academic Pr ess.