Evolutionary loss of the ß1-adrenergic receptor in salmonids

Abstract

Whole-genome duplications (WGDs) have been at the heart of the diversification of β-adrenergic receptors (β-ARs) in vertebrates. Non-teleost jawed vertebrates typically possess three β-AR genes:adrb1(β1-AR),adrb2(β2-AR), andadrb3(β3-AR), originating from the ancient 2R (two rounds) WGDs. Teleost fishes, owing to the teleost-specific WGD, have five ancestraladrbparalogs (adrb1,adrb2a,adrb2b,adrb3aandadrb3b). Salmonids are particularly intriguing from an evolutionary perspective as they experienced an additional WGD after separating from other teleosts. Moreover, adrenergic regulation in salmonids, especially rainbow trout, has been intensively studied for decades. However, the repertoire ofadrbgenes in salmonids has not been yet characterized. An exhaustive genome survey of diverse salmonids, spanning five genera, complemented by phylogenetic sequence analysis, revealed each species has sevenadrbparalogs: twoadrb2a, twoadrb2b, twoadrb3aand oneadrb3b. Surprisingly, salmonids emerge as the first known jawed vertebrate lineage to lackadrb1.adrb1is nevertheless highly expressed in the hearts of non-salmonid teleosts, indicating that the wealth of data on adrenergic regulation in salmonids should be generalised to other teleost fishes with caution. It is hypothesised that the loss ofadrb1could have been viable because of the evolutionary radiation ofadrb2andadrb3genes attributable to the salmonid WGD.