Evolution of the glucagon-like system across fish

Area of Science:

• Comparative endocrinology
• Evolutionary biology
• Genomics

Background:

• Plasma glucose regulation in fish is more variable than in mammals.
• The glucagon (GCG)-like peptide family regulates glucose and lipids in both fish and mammals.
• Fish possess additional glucagon-like gene family members (gcrp and gcrpr) absent in mammals.

Purpose of the Study:

• To analyze the evolution of the glucagon-like system in fish.
• To characterize the gene expression of glucagon-like family members in the European sea bass (Dicentrarchus labrax).

Main Methods:

• Phylogenetic analysis of glucagon-like family genes.
• Synteny analysis to investigate gene loss.
• Gene expression analysis (tissue distribution) in European sea bass.
• Correlation of gene expression with plasma glucose levels.

Main Results:

• Multiple glucagon-like receptors and peptides emerged early in vertebrate evolution, with lineage-specific diversification.
• Gene loss within the family likely resulted from a single deletion event.
• European sea bass exhibited variable tissue distribution of glucagon-like system transcripts, suggesting distinct functions.
• Down-regulation of teleost proglucagon a in sea bass correlated with altered plasma glucose levels.

Conclusions:

• The glucagon-like system in fish has evolved distinct pathways compared to mammals.
• Despite conserved elements, the brain-gut-peptide regulatory loop diverged between teleosts and mammals.
• Glucagon-like peptides play a significant role in regulating fish metabolism.