Down-regulation of Drosophila Egf-r mRNA levels following hyperactivated receptor signaling.

Internalization of ligand-receptor complexes is a well-documented mechanism for limiting the duration and magnitude of a signaling event. In the case of the EGF-Receptor (EGF-R), exposure to EGF or TGF-alpha results in internalization of up to 95% of the surface receptor pool within 5 minutes of exposure to ligand. In this report, we show that levels of Drosophila Egf-r mRNA are strongly down-regulated in epidermal cells likely to have recently undergone high levels of EGF-R signaling. The cells in which Egf-r mRNA levels are down-regulated express the rhomboid gene, which is thought to locally amplify EGF-R signaling. Widespread Egf-r mRNA down-regulation can be induced by ubiquitous expression of rhomboid or by eliminating the Gap1 gene. These results suggest that cells engaged in intense EGF-R/RAS signaling limit the duration of the signal through a combination of short-acting negative feedback mechanisms such as receptor internalization followed by a longer lasting reduction in receptor transcript levels. Control of Egf-r mRNA levels by altering transcription or mRNA stability is a new tier of regulation to be considered in analysis of EGF-R signaling during development.