Putative new groups of invertebrate water channels based on the snail Helix pomatia L. (Helicidae) MIP protein identification and phylogenetic analysis

Molecular Characterization of Aquaporins Genes from the Razor Clam Sinonovacula constricta and Their Potential Role in Salinity Tolerance

Aquaporins (AQPs) play crucial roles in osmoregulation, but the knowledge about the functions of AQPs in Sinonovacula constricta is unclear. In this study, Sc-AQP1, Sc-AQP8, and Sc-AQP11 were identified from S. constricta, and the three Sc-AQPs are highly conserved compared to the known AQPs. The qRT-PCR analysis revealed that the highest mRNA expressions of Sc-AQP1, Sc-AQP8, and Sc-AQP11 were detected in the gill, digestive gland, and adductor muscle, respectively. In addition, the highest mRNA expression of Sc-AQP1 and Sc-AQP11 was detected in the D-shaped larvae stage, whereas that of SC-AQP8 was observed in the umbo larvae stage. The mRNA expression of Sc-AQP1, Sc-AQP8, and Sc-AQP11 significantly increased to 12.45-, 12.36-, and 27.44-folds post-exposure of low salinity (3.5 psu), while only Sc-AQP1 and Sc-AQP11 significantly increased post-exposure of high salinity (35 psu) (p < 0.01). The fluorescence in situ hybridization also showed that the salinity shift led to the boost of Sc-AQP1, Sc-AQP8, and Sc-AQP11 mRNA expression in gill filament, digestive gland, and adductor muscle, respectively. Knockdown of the Sc-AQP1 and Sc-AQP8 led to the decreased osmotic pressure in the hemolymph. Overall, these findings would contribute to the comprehension of the osmoregulation pattern of AQPs in S. constricta.

Diversification of the aquaporin family in geographical isolated oyster species promote the adaptability to dynamic environments

BACKGROUND

The diversified aquaporin (AQP) family that was derived from gene duplication and subsequent functional differentiation play critical roles in multiple physiological processes and in adaptation to the dynamic environments during the evolutionary process. Oysters are a group of bivalve fauna in Mollusca that were widely distributed around the world and show extraordinary adaptation to harsh environments. However, knowledge is lacking with the diversity and evolution of the AQP family in oysters, even in molluscs.

RESULTS

Here, we performed a comprehensive analysis of the AQP family in three geographical isolated oyster species that are native to different environments. Genome distribution and phylogenetic analysis revealed that the expansion of the AQP family in oysters were attributed to tandem duplication. Synteny analysis indicated that large-scale inversions lead to the independent duplication or deletion of the AQPs after speciation. As a consequence, these independent duplication events contributed to the diversification of the AQP family in different oysters. Pore pattern analysis suggested that the duplicated AQPs in oysters were highly diversified in inner surface profiles, implying the subsequent functional differentiation. The comparison conducted based on the transcriptome data demonstrated that the functional differentiated AQP family members in oysters may play critical roles in maintaining the balance between the stationary homeostasis and dynamic environments.

CONCLUSIONS

Our observation provides evidence for the correlation between the duplicated and functional differentiated AQP family and the adaptation to stationary life under dynamic environments in oysters. Additionally, it also broadens our knowledge of the evolution of AQP family in molluscs.

Duplication and subsequent functional diversification of aquaporin family in Pacific abalone Haliotis discus hannai

Aquaporins (AQPs) are a group of proteins that evolved to mediate specific permeation of water and other small solutes, playing important roles in osmoregulation and nutrition, especially for aquatic animals. Genome-wide characterization of the AQP family in a typical mollusc, Pacific abalone, suggested that tandem duplication and retroduplication led to the dramatic expansion and diversification of AQP genes. Structural analysis indicated that tandem duplicated AQPs showed abnormal characteristics. The conserved amino acids in the key site of the Ar/R region were replaced by the others. These substitutions altered the pore diameter and properties of the inner surface and could accommodate the pass through of other molecules except water. Functional analysis indicated that abnormal Ar/R region of the tandemly adjacent members led to the different permeability, suggesting the neofunctionalization of tandemly duplicated genes. Mutation analysis indicated that at the key site of Ar/R region, just a single amino acid substitute could alter the permeability of HdAQPs, further explaining the mechanism of neofunctionalization between the tandem duplicated HdAQPs. Our observations provided strong evidence that duplication and subsequent neofunctionalization have led to structural and functional diversity of AQPs in Pacific abalone, providing insights into the evolution of AQPs in molluscs.

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

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.

The quagga mussel genome and the evolution of freshwater tolerance

Freshwater dreissenid mussels evolved from marine ancestors during the Miocene ∼30 million years ago and today include some of the most successful and destructive invasive species of freshwater environments. Here, we sequenced the genome of the quagga mussel Dreissena rostriformis to identify adaptations involved in embryonic osmoregulation. We provide evidence that a lophotrochozoan-specific aquaporin water channel, a vacuolar ATPase subunit and a sodium/hydrogen exchanger are involved in osmoregulation throughout early cleavage, during which time large intercellular fluid-filled 'cleavage cavities' repeatedly form, coalesce and collapse, expelling excess water to the exterior. Independent expansions of aquaporins coinciding with at least five freshwater colonization events confirm their role in freshwater adaptation. Repeated aquaporin expansions and the evolution of membrane-bound fluid-filled osmoregulatory structures in diverse freshwater taxa point to a fundamental principle guiding the evolution of freshwater tolerance and provide a framework for future species control efforts.

A phylogenetic classification of gastropod aquaporins

Successful responses to the multifarious challenges of controlling water balance are critical for snails' survival in the great diversity of habitats they occupy. Advances are being made in understanding how such challenges are approached at the molecular level, including through the study of aquaporins, which are proteins functioning to facilitate the passage of water and other small molecules across cellular membranes. Deduced aquaporin amino acid sequences from partial genomic assemblies of three neritimorph species were added to available gastropod data and sequences from other taxa to make a phylogenetic classification of these proteins using maximum likelihood and Bayesian analyses. We identified ten groups, designated as G1 to G10, containing sequences from multiple major gastropod lineages. At least six of the groups appear to be encoded by multiple genes within at least some species. Five weakly-associated sequences from Neritimorpha were not allocated to a group. The designated groups G1, G2, G3, G4, G5 and G7 (previously defined as Malacoglyceroporins) formed clades containing only gastropod sequences and were strongly supported by Bayesian inference. G1, G2, G3 and G5 were also strongly supported by maximum likelihood analyses. Group G6 (previously defined as Malacoaquaporins)was included with sequences from the oyster, Crassostrea gigas in a strongly supported clade. Groups G8 and G9 included only gastropod sequences but were not strongly supported. Groups G8 and G10 were designated to include all the gastropod sequences belonging respectively to strongly-supported clades including human aquaglyceroporins and aquaammoniaporins. Most groups have been found in a wide range of gastropod lineages but all identified representatives of group G7 belong to Apogastropoda whereas G2 is known only from Patellogastropoda and Neritimorpha.