A dynamic cycle of O-linked N-acetylglucosamine (O-GlcNAc) addition and removal acts on nuclear pore proteins, transcription factors, and kinases to modulate cellular signaling cascades. This nutrient sensing hexosamine signaling pathway is conserved from nematodes to man. A single nucleotide polymorphism in the human O-GlcNAcase gene is linked to type 2 diabetes, suggesting that perturbation of this pathway results in disease.? ? In collaboration the Hanover lab (NIDDK), we showed that the C. elegans genome encodes the two evolutionarily conserved enzymes that mediate O-GlcNAc cycling, with the genes called ogt-1 and oga-1. We previously characterized a knockout allele of ogt-1 gene. Now, we demonstrate that oga-1 encodes an active O-GlcNAcase when expressed in E. coli and we describe a knockout allele, oga-1 (ok1207), that is viable and fertile yet accumulates O-GlcNAc on nuclear pores and other cellular proteins. Interfering with O-GlcNAc recycling with either oga-1(ok1207) or the O-GlcNAc transferase null ogt-1(ok430) globally altered Ser- and Thr-phosphorylation and specifically increased phospho-GSK-3 levels. Like ogt-1(ok430), the oga-1(ok1207) strain exhibited elevated glycogen and trehalose stores and decreased lipid storage suggesting that the insulin-like signaling pathway controlling storage, longevity and dauer formation was perturbed by inhibiting O-GlcNAc cycling. Furthermore, the oga-1(ok1207) knockout augmented an alternate developmental life cycle (dauer formation) as assayed by a temperature sensitive allele of the insulin-like receptor (daf-2). Under the same conditons, the ogt-1(ok430) mutant diminished dauer formation. Our findings suggest that the highly conserved enzymes of O-GlcNAc recycling fine-tune insulin-like signaling in C. elegans in response to nutrient flux. The knockout of O-GlcNAcase in C. elegans mimics many of the metabolic and signaling changes associated with human insulin resistance and may provide a genetically amenable model of non-insulin dependent diabetes. ? ? We have continued to take advantage of these viable strains that lack O-GlcNAc cycling activity to explore the role of nutrient flux in development. Using a combination of genomic expression arrays and chromatin immunoprecipitation (ChIP) we are looking for genes that respond to nutrient flux differently in the mutants with the hope of identifying pathways of importance.
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