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.
Highlights
We identified a total of 401 annelid Aqps from 27 annelid species, belonging to 16 families (i.e., 12 Sedentaria and four Errantia)
Three of these sequences were annotated as Aqps in the widely used nr database of NCBI
The distribution of the identified annelid sequences among the different Aqp groups indicates that no major Aqp clade previously found in other invertebrates/vertebrates was absent in the two main annelid groups of Errantia and Sedentaria (Figure 1)
Summary
Estuaries, including a large variety of intertidal environments, are highly dynamic systems characterized by large salinity fluctuations due to regular or stochastic events, such as pluviosity, river flows, tides, waves and storms [1]. Regular or irregular salinity variation is a major ecological and evolutionary challenge faced by organisms inhabiting these environments, which exhibit adaptations at different levels of biological organization. Complex excretory systems and less permeable cuticles are common [2,3,4]. Membrane carrier and channel proteins work together to regulate osmolarity and cell volume. For instance, function to transport ions and neutral solutes through the plasma membranes.
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