In a previous study, UW anatomy professor John F. Fallon and his team showed that Sonic hedgehog (Shh) and bone morphogenetic protein 2 (Bmp2) must be expressed in order to produce barb ridges, which are among the first structures to form in the tufted branches of the simple downy chick feather. The two proteins, which tend to play off each other in organ development, also are involved in the embryonic development of limbs, lungs, teeth and the gut.
In the current study, appearing in the Aug. 16 Proceedings of the National Academy of Sciences (PNAS Online, Aug. 8), Fallon's team and collaborators showed that during the development of barbs-filamentous structures that form the feather-the function of these two proteins interact. SHH up-regulates its own expression and that of Bmp2, and Bmp2 then signals the down-regulation of Shh expression. This dynamic signaling interaction fits a longstanding mathematical model known as an activator-inhibitor mechanism, says lead author Matthew P. Harris, Fallon's graduate student now doing a postdoctoral fellowship with Nobel Laureate Christiane Nusslein-Volhard at Max Plank Institute in Tubingen, Germany.
"In this model, the inhibitor down-regulates activator function, the activator up-regulates its own expression and the activator also increases the activity of the inhibitor," Harris says. "The model is a simple way of explaining how feather patterning is achieved."
Theoretical biologist Hans Meinhardt, also at the Max Plank Institute and a collaborator on the PNAS paper, posited the role of the activator-inhibitor model in developmental patterning in animals years ago. Through the combined efforts of Meinhar
Contact: John Fallon
University of Wisconsin-Madison