Deficient Notch signaling associated with neurogenicpecanexis compensated for by the unfolded protein response inDrosophila

Abstract

SUMMARYThe Notch (N) signaling machinery is evolutionarily conserved and regulates a broad spectrum of cell-specification events, through local cell-cell communication. pecanex (pcx) encodes a multi-pass transmembrane protein of unknown function, widely found from Drosophila to humans. The zygotic and maternal loss of pcx in Drosophila causes a neurogenic phenotype (hyperplasia of the embryonic nervous system), suggesting that pcx might be involved in N signaling. Here, we established that Pcx is a component of the N-signaling pathway. Pcx was required upstream of the membrane-tethered and the nuclear forms of activated N, probably in N signal-receiving cells, suggesting that pcx is required prior to or during the activation of N. pcx overexpression revealed that Pcx resides in the endoplasmic reticulum (ER). Disruption of pcx function resulted in enlargement of the ER that was not attributable to the reduced N signaling activity. In addition, hyper-induction of the unfolded protein response (UPR) by the expression of activated Xbp1 or dominant-negative Heat shock protein cognate 3 suppressed the neurogenic phenotype and ER enlargement caused by the absence of pcx. A similar suppression of these phenotypes was induced by overexpression of O-fucosyltransferase 1, an N-specific chaperone. Taking these results together, we speculate that the reduction in N signaling in embryos lacking pcx function might be attributable to defective ER functions, which are compensated for by upregulation of the UPR and possibly by enhancement of N folding. Our results indicate that the ER plays a previously unrecognized role in N signaling and that this ER function depends on pcx activity.

Maternal almondex, a neurogenic gene, is required for proper subcellular Notch distribution in early Drosophila embryogenesis

“…Embryos were hybridized in situ as described previously (Takashima & Murakami, ). RNA probes of single‐minded ( sim ) were prepared as previously described (Yamakawa et al, ).…”

O-Fucose Monosaccharide of Drosophila Notch Has a Temperature-sensitive Function and Cooperates with O-Glucose Glycan in Notch Transport and Notch Signaling Activation

“…We identified the ER (Boca and Pdi), Golgi (GM130), early endosomes (Hrs), late endosomes (Rab7), recycling endosomes (Rab11), and lysosomes (Lamp) by immunostaining (25,36,51,52,54). In wingdisc epithelial cells, the ER was detected either as an indistinct and shapeless structure (Fig.…”

Unraveling Genetic Modifiers in the Gria4 Mouse Model of Absence Epilepsy

“…This IAP is integrated in the 5′-LTR-3-′LTR orientation in intron 19 of Pcnxl2 , the gene that encodes pecanex-like 2. Pcnxl2 is one of three mammalian paralogs of Drosophila melanogaster pecanex, a neurogenic gene about which little is known, but was recently suggested to be part of the notch signaling pathway in the endoplasmic reticulum [24], [25]. In adult mouse brain, Pcnxl2 is expressed highest in the hippocampal pyramidal cell layer, it is also expressed prominently in the area of cerebral cortex corresponding to layer V, and sparsely in the reticular thalamic nucleus (Allen Brain Atlas: see http://mouse.brain-map.org/experiment/show/70239051).…”

“…But no known primary or predicted secondary structures have been identified that would predict further function. D. melanogaster pecanex ( pcnx ) localizes to the endoplasmic reticulum (ER) and functional genetic studies utilizing the protein unfolded response as a readout, suggest that it shows maternal inheritance and has a role in notch signaling [25]. From conservation among pecanex family members we might expect that Pcnxl2 is also expressed in the ER.…”