Cnc, maf S, and Deaf 1 are reported to interact with the Hox protein Deformed to regu late segmentation, but their roles in other developmental events are not known. Our results provide a possi ble role of STI571 these proteins in Drosophila development by promoting Notch signaling. Another transcription factor that we found to play an agonistic role in Notch signaling is the homeobox con taining protein Aristaless. Al has been tentatively linked to Notch signaling, as it cell autono mously represses the Notch ligand Delta in the pretarsus during leg morphogenesis. It is possible that al is involved in a Notch mediated lateral inhibition mechan ism, where al expressing cells remain undifferentiated by favoring active Notch signaling whereas their neighbor ing cells are free to express Delta and differentiate.

It has also been shown that Notch mutant clones in the developing leg disk show diminished al levels, suggesting that al is a Notch target gene. This would be the pre dicted relationship in a lateral inhibition system, where a Notch al positive feedback loop would amplify the Notch activity differences between neighboring cells. Two additional transcription factors that have been previously shown to be involved in leg morphogenesis were found to promote Notch signaling, Bonus, a homologue of the vertebrate TIF1beta transcriptional cofactor, and crooked legs, a zinc finger pro tein. Notch signaling is known to play an important role in Drosophila leg development, and the recovery of these two transcription factors as modifiers of Notch induced E m3 expression suggests that bon and croI may function to modulate Notch target gene output in the developing leg.

We also identified the Drosophila orthologues of two mammalian proto oncogenes kayak, and c Myb, as positive regulators of Notch signaling. Although a direct functional link between these proteins and Notch signaling has not been described, kayak has been shown to interact genetically with Hairless and c Myb genetically interacts with bon, a novel Notch modifier described above. In addition, our data reveals a synergistic relationship between the positive regulator of Ras signaling, 14 3 3��, and Notch. Once again, the pro tein interaction network shows extensive contacts between 14 3 3�� and the chromatin machinery, suggest ing a mechanism for modulating Notch target transcrip tion through Su mediated chromatin modifications.

Interactions between Notch and oncogenic pathways are of particular interest, as the involvement of Notch in cancer biology and stem cell maintenance is becoming increasingly apparent. An unexpected Notch target transcription modifier identified in the screen is the Notch target gene Tram track. We found that targeting of ttk with dsRNA resulted in reduced Notch activity. In contrast, ttk expression itself has been shown to increase Batimastat in response to ectopic Notch activity.