DIFFERENTIAL EXPRESSION OF FOS AND JUN FAMILY MEMBERS IN THE DEVELOPING CHICKEN GASTROINTESTINAL-TRACT

We have analysed the expression patterns of all the known fos/jun fami ly genes, which encode the components of the transcription factor AP-1 , in the chicken embryonic digestive tract that develops into the esop hagus, proventriculus, gizzard, small intestine, ceca and large intest ine, From soon after formation of the tubular structure, each gene tra nscript was localized in distinct domains of the epithelium and mesenc hyme in all of these major gastrointestinal organs, independently of t he anterior-posterior axis, fra-2 was expressed predominantly in epith elium, which also expressed junD, while low-level expression of junD w as also detected in smooth muscle cell precursors in mesenchyme, Expre ssion of c-jun and c-fos was detectable in both mesenchyme and epithel ium through the whole tract, In the differentiated proventriculus, the developed glandular epithelium expressed c-jun and junD, but not fra- 2, while luminal epithelium expressed fra-2 and junD, but not c-jun. T hese results suggest that distinct Fos/Jun protein heterodimers play i mportant roles in maintaining the epithelial-mesenchymal interactions. Similar expression patterns to those of fra-2 and junD were establish ed from earlier stages by Sonic hedgehog gene and the Indian hedgehog gene, respectively, both of which are important in forming the inducti ve network between epithelium and mesenchyme of the digestive tract.