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 investigated in developing avian gut. Expression is restricted to the epithelial layer of the embryonic proventriculus (glandular stomach). We can therefore regard this gene as a marker gene for proventricular epithelial differentiation. There is some considerable evidence in favour of epithelial-mesenchymal interactions being important during the development of the gastrointestinal system; for example, pepsinogen expression is induced in proventricular and gizzard (muscular stomach) epithelial by the proventricular mesenchyme but is suppressed by the gizzard mesenchyme. In the present paper, we studied how the mesenchymes influence this gene expression pattern. For this we produced constructs containing various portions of the 5'-flanking region of the embryonic chick pepsinogen gene, driving reporter sequences (beta-galactocidase or luciferase), and these constructs were transfected into dissociated epithelial cells either from the proventriculus or gizzard. We then recombined these cells with mesenchymal cells and cultured them as cell aggregates. In this way, we were able to dissect the timing and other requirements of the epithelial-mesenchymal interactions for expression of embryonic chick pepsinogen gene. We also report that 1.1 kb of 5'-flanking sequence is sufficient to drive correct expression of embryonic chick pepsinogen gene, although further enhancement was seen if the constructs contained 3.2 kb of upstream sequence.