MESENCHYMAL REGULATION OF EPITHELIAL GENE-EXPRESSION IN DEVELOPING AVIAN STOMACH - 5'-FLANKING REGION OF PEPSINOGEN GENE CAN MEDIATE MESENCHYMAL INFLUENCE ON ITS EXPRESSION

The expression of a gene encoding an embryonic chick pepsinogen was in vestigated in developing avian gut, Expression is restricted to the ep ithelial layer of the embryonic proventriculus (glandular stomach), We can therefore regard this gene as a marker gene for proventricular ep ithelial differentiation. There is some considerable evidence in favou r of epithelilal-mesenchymal interactions being important during the d evelopment of the gastrointestinal system; for example, pepsinogen exp ression is induced in proventricular and gizzard (muscular stomach) ep ithelia by the proventricular mesenchyme but is suppressed by the gizz ard mesenchyme. In the present paper, we studied how the mesenchymes i nfluence this gene expression pattern, For this we produced constructs containing various portions of the 5'-flanking region of the embryoni c chick pepsinogen gene, driving reporter sequences (beta-galactocidas e or luciferase), and these constructs were transfected into dissociat ed epithelial cells either from the proventriculus or gizzard, We then recombined these cells with mesenchymal cells and cultured them as ce ll aggregates. In this way, we were able to dissect the timing and oth er requirements of the epithelial-mesenchymal interactions for express ion of embryonic chick pepsinogen gene, We also report that 1.1 kb of 5'-flanking sequence is sufficient to drive correct expression of embr yonic chick pepsinogen gene, although further enhancement was seen if the constructs contained 3.2 kb of upstream sequence.