Gizzard formation and the role of Bapx1

The anterior-posterior gut pattern is formed from three broad domains: fore -, mid-, and hindgut that have distinct functional, morphological, and mole cular boundaries. The stomach demarcates the posterior boundary of the fore gut. Avian stomachs are composed of two chambers: the anterior chamber (pro ventriculus) and the thick muscular posterior chamber (gizzard). Expression of candidate pattern formation control factors are restricted in the chick stomach regions such that Bmp4 and Wnt5a are not expressed in the gizzard. We previously implicated Bmp4 as controlling growth and differentiation of the gut musculature. Bmp4 is not expressed in the developing gizzard but i s expressed in the rest of the gut including the adjacent proventriculus an d midgut. Bapx1: (Nkx3.2) is expressed in the gizzard musculature but not i n the proventriculus or midgut. We show ectopic expression of Bapx1 in the proventriculus results in a gizzard-like morphology and inhibits the normal proventricular expression of Bmp4 and Wnt5a. Overexpression of a reverse-f unction Bapx1 construct can result in a small stomach and ectopic extension of Bmp4 and Wnt5a expression into the gizzard. We suggest the role of Bapx 1 is to regulate the expression of Bmp4 and Wnt5a to pattern the avian stom ach. (C) 2001 Academic Press.