Two differing precursor genes for the salmon-type gonadotropin-releasing hormone exist in salmonids

Area of Science:

• Molecular Biology
• Reproductive Biology
• Genetics

Background:

• Salmon gonadotropin-releasing hormone (sGnRH) is crucial for regulating reproduction in salmonid fish.
• Understanding the molecular mechanisms of sGnRH is essential for comprehending reproductive physiology.

Purpose of the Study:

• To characterize the nucleotide sequences of two types of cDNAs encoding sGnRH precursors in sockeye salmon (Oncorhynchus nerka).
• To investigate the genetic basis of sGnRH diversity in salmonids.

Main Methods:

• Cloning strategy based on reverse transcription-polymerase chain reaction (RT-PCR) to identify sGnRH cDNAs.
• Northern blot analysis to confirm the presence of corresponding mRNAs in various salmonid species.
• Southern blot analysis to support the existence of multiple sGnRH genes.

Main Results:

• Two distinct sGnRH precursor cDNAs, ss-pro-sGnRH-I and -II, were identified in sockeye salmon, with lengths of 435 and 481 bases, respectively.
• Both precursors contain predicted signal peptides, the sGnRH hormone, and a GnRH-associated peptide.
• Northern blot analysis confirmed the presence of two types of sGnRH mRNAs in sockeye salmon, masu salmon, and rainbow trout.
• Sequence comparisons revealed significant identity between sockeye salmon and other salmonid sGnRH cDNAs, indicating conserved but distinct genes.
• Southern blot analysis provided genetic evidence for the presence of at least two sGnRH genes in sockeye salmon, masu salmon, and rainbow trout.

Conclusions:

• Sockeye salmon possesses two different genes encoding sGnRH precursors.
• The findings suggest that multiple sGnRH genes are present across different salmonid species, contributing to reproductive diversity.
• This study provides a molecular basis for understanding the complex regulation of reproduction in salmonids.