A Genetic Model to Study Increased Hexosamine Biosynthetic Flux

Area of Science:

• Zebrafish genetics
• Metabolic pathways
• Molecular biology

Background:

• Hepatic steatosis and developmental arrest were observed in the recessive zebrafish mutant harvest moon (hmn).
• The hmn mutation affects the hexosamine biosynthetic pathway (HBP), crucial for cellular metabolism.

Purpose of the Study:

• To identify the genetic basis of the hmn mutation.
• To characterize the physiological defects associated with altered HBP function.
• To investigate the role of O-linked N-acetylglucosamine (O-GlcNAc) modification in metabolic regulation.

Main Methods:

• Positional cloning and fine mapping to identify the mutated gene.
• Genetic analysis of zebrafish mutants.
• Biochemical assays to measure triacylglycerol levels and protein abundance.
• Analysis of O-GlcNAc modification levels and blood glucose in mutants.

Main Results:

• The hmn mutation is a point mutation in the glutamine-fructose-6-phosphate transamidase 1 (Gfpt1) gene, the rate-limiting enzyme of the HBP.
• Gfpt1 mutants exhibit increased protein O-GlcNAc modification.
• Mutants display hepatic steatosis, developmental arrest, and reduced fasting blood glucose in males, indicating insulin resistance without hyperglycemia.

Conclusions:

• Global increase in O-GlcNAc modification, driven by Gfpt1 mutation, causes specific insulin resistance phenotypes like hepatic steatosis and runting.
• The hmn zebrafish model offers a platform to explore the complex relationship between O-GlcNAc modification and insulin responsiveness across tissues.
• Altered HBP function impacts glucose homeostasis and development, highlighting its significance in metabolic health.