Phylogenomic and functional analyses of salmon lice aquaporins uncover the molecular diversity of the superfamily in Arthropoda.

Jon Anders Stavang,Francois Chauvigné,Roderick Nigel Finn,Heidi Kongshaug,Frank Nilsen,Joan Cerdà

doi:10.1186/s12864-015-1814-8

Jon Anders Stavang, Francois Chauvigné + Show 4 more

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BackgroundAn emerging field in biomedical research is focusing on the roles of aquaporin water channels in parasites that cause debilitating or lethal diseases to their vertebrate hosts. The primary vectorial agents are hematophagous arthropods, including mosquitoes, flies, ticks and lice, however very little is known concerning the functional diversity of aquaporins in non-insect members of the Arthropoda. Here we conducted phylogenomic and functional analyses of aquaporins in the salmon louse, a marine ectoparasitic copepod that feeds on the skin and body fluids of salmonids, and used the primary structures of the isolated channels to uncover the genomic repertoires in Arthropoda.ResultsGenomic screening identified 7 aquaporin paralogs in the louse in contrast to 42 in its host the Atlantic salmon. Phylogenetic inference of the louse nucleotides and proteins in relation to orthologs identified in Chelicerata, Myriapoda, Crustacea and Hexapoda revealed that the arthropod aquaporin superfamily can be classified into three major grades (1) classical aquaporins including Big brain (Bib) and Prip-like (PripL) channels (2) aquaglyceroporins (Glp) and (3) unorthodox aquaporins (Aqp12-like). In Hexapoda, two additional subfamilies exist as Drip and a recently classified entomoglyceroporin (Eglp) group. Cloning and remapping the louse cDNAs to the genomic DNA revealed that they are encoded by 1–7 exons, with two of the Glps being expressed as N-terminal splice variants (Glp1_v1, −1_v2, −3_v1, −3_v2). Heterologous expression of the cRNAs in amphibian oocytes demonstrated that PripL transports water and urea, while Bib does not. Glp1_v1, −2, −3_v1 and −3_v2 each transport water, glycerol and urea, while Glp1_v2 and the Aqp12-like channels were retained intracellularly. Transcript abundance analyses revealed expression of each louse paralog at all developmental stages, except for glp1_v1, which is specific to preadult and adult males.ConclusionsOur data suggest that the aquaporin repertoires of extant arthropods have expanded independently in the different lineages, but can be phylogenetically classified into three major grades as opposed to four present in deuterostome animals. While the aquaporin repertoire of Atlantic salmon represents a 6-fold redundancy compared to the louse, the functional assays reveal that the permeation properties of the different crustacean grades of aquaporin are largely conserved to the vertebrate counterparts.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1814-8) contains supplementary material, which is available to authorized users.

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An emerging field in biomedical research is focusing on the roles of aquaporin water channels in parasites that cause debilitating or lethal diseases to their vertebrate hosts
Each putative mRNA sequence was isolated and cloned using gene-specific primers and rapid amplification of cDNA ends (RACE) analyses. This resulted in 9 cDNAs with open reading frames ranging in length from 777–1992 bp, encoding proteins of 258–663 amino acids, which, following phylogenetic analyses, we termed Big brain (Bib), Pyrocoelia rufa integral protein (Prip)-like (PripL), Glp1-3, Aqp12like1 (Aqp12L1) and Aqp12-like 2 (Aqp12L2) (Fig. 1a)
Alignment and in silico analyses of the secondary and tertiary structures showed that each louse protein consists of six transmembrane domains, two Asn-Pro-Ala (NPA)-like motifs at the termini of two hemihelices, and five loops A – E typically found in mammalian aquaporins [49]

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An emerging field in biomedical research is focusing on the roles of aquaporin water channels in parasites that cause debilitating or lethal diseases to their vertebrate hosts. We conducted phylogenomic and functional analyses of aquaporins in the salmon louse, a marine ectoparasitic copepod that feeds on the skin and body fluids of salmonids, and used the primary structures of the isolated channels to uncover the genomic repertoires in Arthropoda. Aquaporins are protein channels, which are assembled as tetramers in biological membranes to facilitate the rapid, yet selective conductance of water and other small solutes and gasses down their concentration gradients [1]. Each protomer is comprised of a conserved tertiary structure consisting of 6 transmembrane domains with two hemihelices that typically project opposing Asn-ProAla (NPA) motifs as part of a central proton-excluding selectivity filter [2, 3]. High gene copy numbers are found in plants and deuterostome animals, the superfamily has been categorised into four major grades consisting of classical water-selective type aquaporins (Aqp0, −1, −2, −4, −5, -5-like, −6, −14, and −15), Aqp8type aquaamoniaporins (Aqp and −16), aquaglyceroporins (Glp, Aqp3, −7, 9, −10 and −13) and unorthodox aquaporins (Aqp and −12) [9,10,11,12,13]

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