Characterization of a Leptin Receptor Paralog and Its Response to Fasting in Rainbow Trout ().

Leptin is a cytokine that regulates appetite and energy expenditure, where in fishes it is primarily produced in the liver and acts to mobilize carbohydrates. Most fishes have only one leptin receptor (LepR/LepRA1), however, paralogs have recently been documented in a few species. Here we reveal a second leptin receptor (LepRA2) in rainbow trout that is 77% similar to trout LepRA1. Phylogenetic analyses show a salmonid specific genome duplication event as the probable origin of the second LepR in trout. Tissues distributions showed tissue specific expression of these receptors, with highest in the ovaries, nearly 50-fold higher than . Interestingly, was most highly expressed in the liver while hepatic levels were low. Feed deprivation elicited a decline in plasma leptin, an increase in hepatic by one week and remained elevated at two weeks, while liver expression of remained low. By contrast, muscle mRNA increased at one and two weeks of fasting, while adipose was concordantly lower in fasted fish. transcript levels were not affected in muscle and fat. These data show and are differentially expressed across tissues and during feed deprivation, suggesting paralog- and tissue-specific functions for these leptin receptors.