dCtBP-dependent and independent mechanisms of knirps-mediated repression. M.S. Corado 1, E. Bajor 1, M. Fujioka 2, S. Small 1. 1) Department of Biology, New York University, 100 Washington Square East, New York, NY 10003, (212) 998-3965; 2) Kimmel Cancer Institute, Thomas Jefferson University, 1020 Locust Street, Philadelphia, PA 19107, (215) 503-4774.
knirps (kni) encodes a nuclear receptor protein that is expressed in a broad bell-shaped domain in the abdominal region of the developing embryo. Genetic and biochemical experiments have shown that kni may function as a repressive morphogen that establishes stripe borders of the pair-rule gene even-skipped (eve). The stripes affected by kni are controlled by two separate enhancers. One enhancer drives the expression of stripes 4 and 6, which straddle the anterior and posterior borders of the kni domain. A second enhancer drives the expression of stripes 3 and 7, which lie further away from the source of kni protein. Both enhancers are dramatically derepressed in the regions between the stripes in kni mutants. Here, we investigate the mechanism of kni-mediated repression of these two enhancers. Previous experiments suggest that kni-repression involves a physical interaction with the cofactor dCtBP. This interaction involves a specific motif, P-DLS-K, located near the amino terminus of kni. In misexpresion experiments, mutating this site greatly reduced the ability of kni to repress the stripe 3 response in vivo. To test this mechanism further, we examined the expression of eve reporter genes in germ line clones that lack dCtBP. The stripe 4+6 response was severely derepressed in the absense of dCtBP, but no derepression of the stripe 3+7 reponse was observed, suggesting that repression of this enhancer occurs via a dCtBP-independent mechanism. To identify other potential corepressors, we have initiated genetic and two hybrid screens, which will be discussed.