Insight into Notch Signaling Steps That Involve from Dominant-Modifier Screens in .

Notch signaling plays crucial roles in intercellular communications. In , the () gene, which encodes an evolutionarily conserved multi-pass transmembrane protein, appears to be required to activate Notch signaling in some contexts, especially during neuroblast segregation in the neuroectoderm. Although Pcx has been suggested to contribute to endoplasmic reticulum homeostasis, its functions remain unknown. Here, to elucidate these roles, we performed genetic modifier screens of We found that heterozygotes lacking its maternal contribution exhibit cold-sensitive lethality, which is attributed to a reduction in Notch signaling at decreased temperatures. Using sets of deletions that uncover most of the second and third chromosomes, we identified four enhancers and two suppressors of the cold-sensitive lethality. Among these, five genes encode known Notch-signaling components: , (), (), (), a member of the () family, and (). We showed that suppresses Dl endocytosis during neuroblast segregation in the neuroectoderm, as family genes reportedly do in the mesoderm for mesectoderm specification. Analyses of , a key regulator of vesicular fusion, suggested a novel role in neuroblast segregation, which is distinct from Nsf2's previously reported role in imaginal tissues. Finally, , which encodes a potential transcription factor, may play a role in Notch signaling during neuroblast segregation. These results reveal new research avenues for Pcx functions and Notch signaling.