TheN-Glycanasepng-1Acts to Limit Axon Branching during Organ Formation in Caenorhabditis elegans

Abstract

Peptide:N-glycanases (PNGases) are cytoplasmic de-N-glycosylation enzymes that have been shown in cultured cells to facilitate the degradation of misfolded glycoproteins during endoplasmic reticulum-associated degradation and in the processing of major histocompatibility complex class I antigens for proper cell-surface presentation. The gene encoding PNGase activity was initially described in budding yeast (Png1p) and shown to be highly conserved from yeast to humans, but physiological roles in higher organisms have not been elucidated. Here we describe peripheral nervous system defects associated with the first loss-of-function mutations in an animal PNGase. Mutations in png-1, the Caenorhabditis elegans PNGase ortholog, result in an increase in axon branching during morphogenesis of the vulval egg-laying organ and egg-laying behavior changes. Neuronal defects include an increase in the branched morphology of the VC4 and VC5 egg-laying neurons as well as inappropriate branches from axons that run adjacent to the vulva but would normally remain unbranched. We show that png-1 is widely expressed and can act from both neurons and epithelial cells to restrict axon branching. A deletion allele of the DNA repair gene rad-23, orthologs of which are known to physically interact with PNGases in yeast and mammals, displays similar axon branching defects and genetic interactions with png-1. In summary, our analysis reveals a novel developmental role for a PNGase and Rad-23 in the regulation of neuronal branching during organ innervation.

Endo-β- N -acetylglucosaminidase forms N -GlcNAc protein aggregates during ER-associated degradation in Ngly1-defective cells

“…Although Png1 mutants in budding yeast (9) or in plants (42) did not show any significant phenotypic consequences, more recent studies suggests that PNGase orthologs may play important physiological roles in other eukaryotes (43)(44)(45)(46). Recent exome analysis studies have identified human patients with mutations in the NGLY1 gene (24,25).…”

Interplay between redox and protein homeostasis

“…76 In mammalian PNGase this PUB domain is responsible for ERAD substrate interaction. 69 Thus, the role of PNG-1 in ERAD substrate processing remains to be demonstrated. 76 Like the homologous proteins in humans, mouse and yeast, PNG-1 also contains the transglutaminase domain, which is required for PNGase function.…”

“…PNG-1 has been described to act in axon branching, which could be dependent on its PNGase and thioredoxin domain. 69 Using png-1 lossof-function mutants, an increased axon branching was observed. 69 PNG-1, together with its putative interaction partner RAD-23, may process retro-translocated glycopeptides in the cytosol and form bioactive peptides, which are involved in the inhibition of axon branching.…”

“…69 PNG-1, together with its putative interaction partner RAD-23, may process retro-translocated glycopeptides in the cytosol and form bioactive peptides, which are involved in the inhibition of axon branching. 69 Further studies are required to identify more substrates and experimental evidence that PNG-1 is involved in ERAD substrate processing despite the lack of the PUB domain.…”

Nouvelles fonctions de la peptideN-glycanase indépendantes de sa capacité de déglycosylation

“…Des mutants de délétion du gène PNG1 chez Drosophila melanogaster montrent un arrêt ou un ralentissement du développement et une stérilité [29]. La délétion du gène PNG1 entraîne des défauts de polarisation pendant la croissance hyphale du champignon Neurospora crassa [30] et pendant la croissance neuronale chez Caenorhabditis elegans [31]. Ces activités morphogéniques de la PNGase sont indé-pendantes de son activité de déglycosylation : les protéines Png1p de Drosophila melanogaster et de Neurospora crassa sont en effet inactives par défaut d'un motif CXXC (D. melanogaster) [29] ou par l'absence d'un des acides aminés de la triade catalytique (N. crassa) [30].…”