Contents lists available at ScienceDirect Molecular & Biochemical Parasitology journal homepage: www.elsevier.com/locate/molbiopara Genome-wide identification of ABC transporters in monogeneans Víctor Caña-Bozada a , F. Neptalí Morales-Serna a,b, *, Alejandra García-Gasca a , Raúl Llera-Herrera c , Emma J. Fajer-Ávila a a Centro de Investigación en Alimentación y Desarrollo, Unidad Mazatlán en Acuicultura y Manejo Ambiental, Mazatlán 82112, Sinaloa, Mexico b Consejo Nacional de Ciencia y Tecnología (CONACYT), Ciudad de México, Mexico c Unidad Académica Mazatlán, Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Mazatlán 82040, Sinaloa, Mexico ARTICLE INFO Keywords: Platyhelminthes Flatworms Fish parasite Detoxification In silico ABC genes ABSTRACT ATP-Binding Cassette (ABC) transporters are proteins that actively mediate the transport of a wide variety of molecules, including drugs. Thus, in parasitology, ABC transporters have gained attention as potential targets for therapeutic drugs. Among the parasitic Platyhelminthes, ABC transporters have been identified and classified in a few species of Trematoda and Cestoda but not in Monogenea. Monogeneans are mainly ectoparasites of marine and freshwater fish, although they can also be found on other aquatic organisms. Severe epizootics caused by monogeneans have been reported around the world, mainly in confined and/or overcrowded fish. The purpose of this study was to identify the ABC transporters in four species of monogeneans (Gyrodactylus salaris, Protopolystoma xenopodis, Eudiplozoon nipponicum and Neobenedenia melleni) for which genomic resources are publicly available. For comparative purposes, ABC transporters were also identified in endoparasitic (Schistosoma mansoni and Echinococcus granulosus) and free-living (Macrostomun lignano and Schmidtea medi- terranea) platyhelminths. Thirty-two putative ABC transporters were identified in the genome of G. salaris, 40 in the genome of P. xenopodis, 46 in the transcriptome of E. nipponicum and 9 in a rather limited ESTs set available for N. melleni. Of the eight ABC subfamilies (A–H) known in metazoans, subfamily H was the only one not found in any monogenean species. In contrast, ABCC was the best represented subfamily. Phylogenetic analyses showed a few cases of one-to-one orthologous relationships, which agree with results from other metazoan species. We found some monogenean ABC members related to subfamilies B, C and G involved in drug resistance in humans. This information may be useful for future functional studies on ABC transporters in monogeneans. 1. Introduction All organisms have cellular mechanisms of detoxification that comprise the biotransformation and transport of toxic xenobiotics, in- cluding drugs. Among transporter proteins, the ATP-Binding Cassette (ABC) transporters have been recognized by their ability to translocate a variety of substrates, as well as by their ubiquity, with both influx and efflux functions in prokaryotes but only efflux function in eukaryotes ([1] and references therein). The ABC transporters exist on plasma membranes and intracellular compartments. In many genomes, the ABC gene family is the largest family of transporters, which splits into eight subfamilies, designated ABCA through ABCH, although humans have only seven subfamilies (ABCA–ABCG) and plants do not have ABCH but ABCI [2,3]. These proteins contain typically two conserved domains: nucleotide binding domain (NBD) and transmembrane domain (TMD). The NBD binds and hydrolyzes ATP to generate the energy required by the TMD to create a pore for translocation of substrates through the membrane [4]. ABC transporters have gained attention as anti-parasitic drug tar- gets. In parasitic platyhelminths (particularly trematodes), the few studies have been mostly focused on identification and characterization of ABCB and ABCC given their involvement in parasite resistance to different drugs [5,6]. Nonetheless, all other subfamilies have also been found, except for ABCD and ABCH in Schistosoma spp., and ABCE and ABCH in Opisthorchis felineus [5,7]. Interestingly, it was found that in- hibitors of mammalian ABC transporters suppressed the activity of P- glycoproteins (Pgp, member of the subfamily ABCB) in O. felineus, preventing the removal of xenobiotics from the parasite [7]. On this basis, we consider that studies related to ABC transporters should be also performed in flatworms of the class Monogenea, which are mostly ectoparasites of aquatic organisms, infecting mainly gills, skin and fins of marine and freshwater fish around the world. There are https://doi.org/10.1016/j.molbiopara.2019.111234 Received 13 August 2019; Received in revised form 2 November 2019; Accepted 7 November 2019 ⁎ Corresponding author at: Centro de Investigación en Alimentación y Desarrollo, Unidad Mazatlán en Acuicultura y Manejo Ambiental, Mazatlán 82112, Sinaloa, Mexico. E-mail address: francisco.morales@ciad.mx (F.N. Morales-Serna). Molecular & Biochemical Parasitology 234 (2019) 111234 Available online 09 November 2019 0166-6851/ © 2019 Elsevier B.V. All rights reserved. T