Induction of labial expression in the Drosophila endoderm: response elements for dpp signalling and for autoregulation.

Extracellular signal proteins induce the homeotic gene labial (lab) to high levels of localised expression in the endoderm of Drosophila embryos. We aimed to identify cis-regulatory elements within the lab gene that respond to this induction by analysing the activity of stably integrated reporter gene constructs. Dissection of lab 5' flanking sequences reveals two types of response elements. One of these mediates lab dependent activity, providing evidence that lab induction in the endoderm is autoregulatory. The other element, to a large extent independent of lab function, responds to decapentaplegic (dpp), a signal molecule related to mammalian TGF-beta. Our evidence suggests that lab induction in the endoderm reflects coordinate action of two distinct factors one of which may be lab protein itself, and another whose localised activity or expression in the midgut depends on the dpp signal.