Notch (N) signaling is an evolutionarily conserved mechanism that regulates a broad spectrum of cell-specification through local cell-cell interaction. Drosophila pecanex (pcx) encodes an evolutionarily conserved multi-pass transmembrane protein that is a component of N signaling. We previously suggested that Pcx localizes to the endoplasmic reticulum (ER) and is required for the maturation of N receptor in there. However, the functions of pcx in N signaling appears to be context-dependent. Therefore, in this study, we examined the tissue-specific roles of pcx in N and other signaling pathways.
First, we examined various cell-fate decision that requires N signaling activity in pcx mutant embryos. We found that pcx mutant embryos showed abnormalities in the tracheal system, as found in N mutant embryos, suggesting that pcx is required for N signaling in tracheal development. However, pcx was not required for N signaling in the border cells specification of the hindgut and the invagination of the esophagus to the proventriculus.
Unexpectedly, however, the visceral mesodermal cells were missing in pcx mutant embryos, whereas N mutant embryos showed an increase in them as compared with wild-type. These results suggested that pcx is required for a different signaling pathway, besides N signaling. Because mutant embryos of wingless, which encodes a ligand of Wnt signaling, showed the missing of visceral mesodermal cells, it is likely that pcx may be required for Wnt signaling in the visceral mesoderm. In addition, we found that the ER of phagocyte was enlarged in pcx mutant embryos. However, N signaling is not required for the phagocytic development during embryogenesis, and N mutant embryos did not show the ER enlargement phenotype. Thus, we speculated that pcx may function independently of N signaling in phagocytic development. From these results, we concluded that pcx plays cell-type specific functions in N and Wnt signaling pathways.