A novel tilapia prolactin receptor is functionally distinct from its paralog

Area of Science:

• Endocrinology
• Aquaculture
• Molecular Biology

Background:

• Prolactin receptors (PRLR) are crucial for regulating physiological processes in fish.
• Tilapia possess multiple prolactin receptor genes, but their specific roles, especially during environmental stress, remain incompletely understood.

Purpose of the Study:

• To identify and characterize a novel tilapia prolactin receptor (OmPRLR2).
• To investigate the expression patterns, functional responses, and signaling pathways of OmPRLR2 in tilapia, particularly in relation to osmotic stress and sex differences.

Main Methods:

• Identification of OmPRLR2 through gene expression analysis during hyperosmotic stress.
• Comparative sequence analysis of OmPRLR1 and OmPRLR2 with known cytokine class I receptors.
• Quantitative analysis of OmPRLR2 mRNA and protein expression in various tissues under different salinity conditions.
• Functional studies using stably transfected HEK293 cells to assess downstream signaling and salinity tolerance.

Main Results:

• A novel tilapia prolactin receptor, OmPRLR2, was identified with distinct structural features compared to OmPRLR1.
• OmPRLR2 mRNA expression is highest in gills, intestine, kidney, and muscle, with transient increases in gills upon seawater transfer.
• A truncated OmPRLR2 variant, lacking the extracellular domain, is expressed predominantly in males and its expression increases with salinity.
• Overexpression of OmPRLR2 enhances salinity tolerance in HEK293 cells and activates different downstream pathways compared to OmPRLR1.

Conclusions:

• Tilapia possesses at least two distinct prolactin receptor genes (OmPRLR1 and OmPRLR2) with unique functional roles.
• OmPRLR2 plays a significant role in tilapia's adaptation to osmotic stress and exhibits sex-specific expression patterns.
• The truncated OmPRLR2 variant may act as a negative regulator of prolactin signaling during osmotic stress and in male tissues.