GnRH receptors and peptides: skating backward

Area of Science:

• Evolutionary biology
• Endocrinology
• Genomics

Background:

• Gonadotropin-releasing hormone (GnRH) and its receptor are crucial for vertebrate reproduction.
• Vertebrates possess three major GnRH peptide types and two major receptor types, with an unusual distribution pattern.
• Understanding the evolutionary origin of this system is key to comprehending reproductive biology.

Purpose of the Study:

• To investigate the evolutionary history and ancestral state of the GnRH peptide-receptor system in vertebrates.
• To explore the distribution of GnRH receptor types across different vertebrate lineages.
• To examine the relationship between vertebrate and invertebrate GnRH homologs.

Main Methods:

• Genome mining to identify GnRH receptor distribution.
• Phylogenetic analysis of GnRH peptides and receptors.
• Analysis of receptor synteny to infer evolutionary relationships.

Main Results:

• Type I GnRH receptors are present in lobe-finned and cartilaginous fishes, indicating early emergence in vertebrate evolution.
• The little skate and coelacanth possess both type I and II GnRH receptors and all three peptide types, suggesting this was the ancestral vertebrate condition.
• Evidence supports a GnRH superfamily with a common ancestor for vertebrate GnRHs, invertebrate GnRHs, corazonins, and adipokinetic hormones.

Conclusions:

• The ancestral vertebrate likely had three GnRH receptor types and three peptide types before whole genome duplications.
• Invertebrate deuterostomes retain both GnRH and invertebrate GnRH receptors, while vertebrates lost the invertebrate-type system.
• The study clarifies the deep evolutionary origins of the GnRH system, highlighting gene duplication and loss events.