A novel variant of aquaporin 3 is expressed in killifish (Fundulus heteroclitus) intestine

Abstract

Killifish (Fundulus heteroclitus) are euryhaline teleosts that are widely used in environmental and toxicological studies, and they are tolerant to arsenic, in part due to very low assimilation of arsenic from the environment. The mechanism of arsenic uptake by the intestine, a major route of arsenic uptake in humans is unknown. Thus, the goal of this study was to determine if aquaglyceroporins (AQP), which transport water and other small molecules including arsenite across cell membranes, are expressed in the killifish intestine, and whether AQP expression is affected by osmotic stress. Through RT-PCR and sequence analysis of PCR amplicons, we demonstrated that the intestine expresses kfAQP3a and kfAQP3b, two previously identified variants, and also identified a novel variant of killifish AQP3 (kfAQP3c) in the intestine. The variants likely represent alternate splice forms. A BLAST search of the F. heteroclitus reference genome revealed that the AQP3 gene resides on a single locus, while an alignment of the AQP3 sequence among 384 individuals from eight population ranging from Rhode Island to North Carolina revealed that its coding sequence was remarkably conserved with no fixed polymorphism residing in the region that distinguishes these variants. We further demonstrate that the novel variant transports arsenite into HEK293T cells. Whereas kfAQP3a, which does not transport arsenite, was expressed in both freshwater (FW) and saltwater (SW) acclimated fish, kfAQP3b, an arsenic transporter, was expressed only in FW acclimated fish, and kfAQP3c was expressed only in SW acclimated fish. Thus, we have identified a novel, putative splice variant of kfAQP3, kfAQP3c, which transports arsenic and is expressed only in SW acclimated fish.

Comparative transcriptome profiling of selected osmotic regulatory proteins in the gill during seawater acclimation of chum salmon (Oncorhynchus keta) fry

“…According to the findings of the studies of AQPs in F. heteroclitus, Lateolabrax maculatus, O. nerka and S. salar, AQP8 and AQP9 are rarely expressed in gills under the normal condition. The performance of qRT-PCR confirmed that the same was true for chum salmon fry in which AQP8 and AQP9 were hardly expressed in the gill of chum salmon fry in freshwater [47][48][49][50] . However, gene expression of AQP8 and AQP9 in the gill of chum salmon fry sharply increased with salinity increase.…”

Biotransformation of dietary inorganic arsenic in a freshwater fish Carassius auratus and the unique association between arsenic dimethylation and oxidative damage

“…Previous studies found three families of transporters aiding in decreasing cellular As concentrations in fish, including phosphate transporters, aquaglyceroporins (AQP) and multidrug resistance-associated proteins (MRP). It is considered that that As(V) is taken up via the phosphate transporters (Beene et al, 2011), while the uptake and translocation of As(III) are mediated by AQP (Jung et al, 2015).…”

“…Multidrug resistance-associated proteins (MRP) are known to transport a series of anionic substrates including As-glutathione complex out of cells (Shaw et al, 2010). Jung et al (2015) identified a novel variant of AQP3 in Fundulus heteroclitus intestine functioning in As transport and attributed its low bioaccumulation and high resistance to environmental As. Shaw et al (2010) found that the MRP2 expression in the apical membrane of proximal tubules increased when Fundulus heteroclitus were exposed (waterborne) to As(III) for 4-14 d; therefore, the increased As elimination could explain the increased resistance to As in fish.…”

Arsenic Reduces Gene Expression Response to Changing Salinity in Killifish

“…Gill tissue was obtained from male wild killifish sampled from two locations in Maine and one in Virginia. We used fish from Northeast Creek, Maine because we have used these fish extensively in previous experiments. ,,− Fish from Horseshoe Cove Maine, and King’s Creek Virginia were included in the study to ensure that our results would focus on responses shared by multiple killifish populations. We used a nearby Maine population (Horseshoe Cove) because they were easy to collect and expected to be genetically similar to the Northeast Creek population.…”

“…Arsenic is naturally present in bedrock and is released into aquatic systems, particularly in reducing conditions at high pH. 1 Dissolved inorganic arsenic enters cells through sodium/ phosphate cotransporters and water channels, 2 where it may take the place of phosphorus in biochemical reactions or interact with thiol groups in proteins and peptides 3 leading to toxic effects. Many organisms have evolved mechanisms to detoxify arsenic, for example, arsenic methyltransferases, that are highly conserved in nature 4 demonstrating that arsenic is a broadly relevant environmental toxicant.…”