Aquaporin-3 expressed in the basolateral membrane of gill chloride cells in Mozambique tilapia Oreochromis mossambicus adapted to freshwater and seawater

Abstract

We have cloned a homologue of mammalian aquaporin-3 (AQP3) from gills of Mozambique tilapia using a reverse transcription-polymerase chain reaction (RT-PCR). The deduced amino acid sequence shared 64-75% homology with other vertebrate AQP3 homologues. RT-PCR revealed that tilapia AQP3 was expressed in the brain, pituitary, kidney, spleen, intestine, skin, eye and gill in tilapia adapted to freshwater (FW) and seawater (SW). We also examined functional characteristics of tilapia AQP3 using Xenopus oocytes as an in vitro transcribed cRNA expression system. Osmotic water permeability (Pf) of Xenopus oocytes expressing tilapia AQP3 was about 30-fold higher than that of control oocytes, and was 80% inhibited by treatment with 0.3·mmol·l -1 HgCl 2 . Lightmicroscopic immunocytochemistry of branchial epithelia revealed that tilapia AQP3 was expressed in gill chloride cells of FW-and SW-adapted tilapia. Electronmicroscopic immunocytochemistry further demonstrated that tilapia AQP3 was localized in the basolateral membrane of gill chloride cells. Basolateral localization of AQP3 in gill chloride cells suggests that AQP3 is involved in regulatory volume changes and osmoreception, which could trigger functional differentiation of chloride cells.

The effects of acute salinity challenges on osmoregulation in Mozambique tilapia reared in a tidally changing salinity

“…AQP3 has been localized in the basolateral membrane of ionocytes in the gill, which is consistent with its proposed role in cellular volume regulation and as an osmosensor (Watanabe et al, 2005;Madsen et al, 2014). A study using the European eel, Anguilla anguilla, has shown that AQP3 is crucial for maintaining water balance in FW and that when fish are transferred to SW, branchial AQP3 expression is downregulated (Cutler and Cramb, 2002).…”

“…The R 2 values and amplification efficiencies for standard curves were as follows, respectively: 0.993 and 98.2% (elongation factor 1α, EF1α), 0.998 and 95.9% (PRL 188 ), 0.999 and 93.2% (PRLR1), 0.992 and 83.1% (PRLR2), 0.992 and 98.1% (NCC), 0.992 and 89.8% (NKCC1a), 0.997 and 103% (NKAα1a), 0.997 and 98.1% (NKAα1b), 0.984 and 105% (CFTR), 0.968 and 106% (AQP3), and 0.999 and 96.3% (NHE3). All primer pairs employed in this study have been previously described: NCC, NHE3 and NKCC1a (Inokuchi et al, 2008); NKAα1a and NKAα1b ; EF1α (Breves et al, 2010a); PRLR1 (Pierce et al, 2007); PRLR2 (Breves et al, 2010b); AQP3 (Watanabe et al, 2005); CFTR (Moorman et al, 2014); and PRL 188 (Magdeldin et al, 2007). The PCR mixture (15 μl) contained 7.5 µl of 2× Power SYBR Green PCR Master Mix (Life Technologies), 200 nmol l −1 of each primer and 2 µl of cDNA.…”

“…In tilapia, NKAα1a expression predominates in FW-acclimated fish relative to SW-acclimated fish, while NKAα1b expression has been shown to be greater or unchanged in SW-acclimated fish when compared with FW-acclimated fish . Water transport in ionocytes of both FW-and SW-acclimated tilapia is mediated through basolaterally located aquaporin 3 (AQP3) (Watanabe et al, 2005). Together with PRL expression and release, an examination of the expression patterns of genes that encode effectors of ion and water transport can provide a means for investigating how osmoregulatory pathways are governed in a particular environmental salinity rearing regime.…”

Aquaporin expression in the Japanese medaka (Oryzias latipes, Temminck & Schlegel) in FW and SW: challenging the paradigm for intestinal water transport?

“…aqp3a, an aqua-glyceropore, was present at highest levels in skin and gill, which was also the case in tilapia [Oreochromis mossambicus (Watanabe et al, 2005)] and in marine medaka (Kim et al, 2014). In these two tissues, both directly exposed to the external medium, the transcript level was 8-to 10-fold higher in FW than in SW. Interestingly, in mammals AQP3 is localized in the basal epidermal cell layer, where it has been proposed to have a role in skin hydration via its glycerol-transporting properties (HaraChikuma and Verkman, 2006).…”

Kidney morphology and candidate gene expression shows plasticity in sticklebacks adapted to divergent osmotic environments

“…Similar to ATP1A1 and CD2AP, this upregulation in the high-salinity treatment was only observed in the high-salinity population. Interestingly, this expression pattern is opposite to what is generally observed: with the exception of a small sample of tilapia (Oreochromis mossambicus; Watanabe et al, 2005), most euryhaline fish tend to upregulate AQP3 isoforms in freshwater (see Cutler et al, 2007 for a review of AQP3 in teleosts). Such expression differences could reflect localized functional differences in various tubule segments, e.g.…”