Finding Aquaporins in Annelids: An Evolutionary Analysis and a Case Study

Abstract

Aquaporins (AQPs) are a family of membrane channels facilitating diffusion of water and small solutes into and out of cells. Despite their biological relevance in osmoregulation and ubiquitous distribution throughout metazoans, the presence of AQPs in annelids has been poorly investigated. Here, we searched and annotated Aqp sequences in public genomes and transcriptomes of annelids, inferred their evolutionary relationships through phylogenetic analyses and discussed their putative physiological relevance. We identified a total of 401 Aqp sequences in 27 annelid species, including 367 sequences previously unrecognized as Aqps. Similar to vertebrates, phylogenetic tree reconstructions clustered these annelid Aqps in four clades: AQP1-like, AQP3-like, AQP8-like and AQP11-like. We found no clear indication of the existence of paralogs exclusive to annelids; however, several gene duplications seem to have occurred in the ancestors of some Sedentaria annelid families, mainly in the AQP1-like clade. Three of the six Aqps annotated in Alitta succinea, an estuarine annelid showing high salinity tolerance, were validated by RT-PCR sequencing, and their similarity to human AQPs was investigated at the level of “key” conserved residues and predicted three-dimensional structure. Our results suggest a diversification of the structures and functions of AQPs in Annelida comparable to that observed in other taxa.

Parallel duplication and loss of aquaporin-coding genes during the ‘out of the sea’ transition as potential key drivers of animal terrestrialization

“…We identified a total of 27 Aqp-coding genes, in contrast with the one reported by (Mucciolo et al, 2021).…”

“…As we needed to know which aquaporins belonged to which subtype (i.e., classical aquaporins - Aqp1-like, aquaammoniaporins - Aqp3-like, unorthodox aquaporins - Aqp8-like - or superaquaporins - Aqp11-like) for posterior analyses, we first independently classified aquaporins of all animal species included in this study, except for the ones that had already been classified in previous publications (Finn et al 2014; Mucciolo et al 2021). We based this classification on the description of aquaporin phylogenetic clusters and their relative position in the phylogenetic tree to the already classified sequences, which were considered as a backbone.…”

“…In the case of annelids, we dated the species tree using the Aqp1-like gene sequences in MCMCtree (Yang 2007). For that, we first inferred the annelid Aqp1-like gene tree using aquaporins annotated in (Mucciolo et al 2021) and our inferred aquaporins for E. andrei , as our preliminary analyses showed that the aquaporin phylogeny is broadly concordant with the species tree topology at the level of aquaporin subclusters. Second, from this gene tree, we derived 16 sets of 1:1 orthologues with at least four species represented using PhyloPyPruner (Thálen 2019), considering the phylogenetic interrelationships of annelid species as described in (Erséus et al 2020).…”

“…The only exceptions were the aquaporins from the amphibian Leptobrachium leishanense , for which we downloaded the genome annotation (Cunningham et al, 2021). In the case of annelids, (Mucciolo et al, 2021) provided a fairly good representation of aquaporins across Pleistoannelida, the most abundant clade within annelids. However, as noted by the authors, the methodology followed could have underestimated the identification of aquaporins due to the incompleteness or low quality of the source databases’ data.…”

“…This conflict worsens when considering papers on the identification of aquaporins of isolated species without taking their evolutionary history into account (Grohme et al, 2013; Huang et al, 2007). Here, we follow the system used by (Mucciolo et al, 2021) and (Kosicka et al, 2020) but taking into account the gene nomenclature rules, and name each of the aquaporin subtypes as “AqpX-like”, being X the lowest nonzero number of the vertebrate aquaporin coding-gene that forms part of it. Thus, we define the four subtypes as Aqp3-like (aquaglyceroporins), Aqp1-like (classical aquaporins), Aqp8-like (aquaammoniaporins) and Aqp11-like (superaquaporins), and follow this nomenclature hereafter.…”