Marine Fish Egg Hydration Is Aquaporin-Mediated

We investigated the salinity-dependent expression dynamics of seven aquaporin paralogs (aqp1a, aqp3a, aqp7, aqp8ab, aqp10a, aqp10b and aqp11a) in several tissues of euryhaline Japanese medaka (Oryzias latipes). All paralogs except aqp7 and aqp10a had a broad tissue distribution, and several were affected by salinity in both osmoregulatory and non-osmoregulatory tissues. In the intestine, aqp1a, aqp7, aqp8ab and aqp10a decreased upon seawater (SW) acclimation in both long-term acclimated fish and during 1-3 days of the transition period. In the gill, aqp3a was lower and aqp10a higher in SW than in freshwater (FW). In the kidney no aqps were affected by salinity. In the skin, aqp1a and aqp3a were lower in SW than in FW. In the liver, aqp8ab and aqp10a were lower in SW than in FW. Furthermore, six Na + ,K + -ATPase α-subunit isoform transcripts were analysed in the intestine but none showed a consistent response to salinity, suggesting that water transport is not regulated at this level. In contrast, mRNA of the Na + ,K + ,2Cl --cotransporter type-2 strongly increased in the intestine in SW compared with FW fish. Using custom-made antibodies, Aqp1a, Aqp8ab and Aqp10a were localized in the apical region of enterocytes of FW fish. Apical staining intensity strongly decreased, vanished or moved to subapical regions, when fish were acclimated to SW, supporting the lower mRNA expression in SW. Western blots confirmed the decrease in Aqp1a and Aqp10a in SW. The strong decrease in aquaporin expression in the intestine of SW fish is surprising, and challenges the paradigm for transepithelial intestinal water absorption in SW fishes.

Section: Tissue Distribution Of Aquaporins and Nkcc2mentioning

confidence: 77%

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

Madsen

Bujak

Tipsmark

2014

“…The mechanisms of rainbow trout oocyte hydration thus remain unknown and require specific investigations. In the marine teleost, seabream (Sparus aurata) it was recently shown that oocyte hydration is aquaporin mediated (Fabra et al, 2005). Therefore, it is possible that a similar membrane-mediated mechanism also occurs in rainbow trout.…”

Section: Discussionmentioning

confidence: 99%

Hydration of rainbow trout oocyte during meiotic maturation andin vitroregulation by 17,20β-dihydroxy-4-pregnen-3-one and cortisol

Milla¹,

Jalabert²,

Rime³

et al. 2006

Although oocytes of many teleost fish, especially marine species, are subjected to a hydration process during meiotic maturation, which leads to an important volume increase, no noticeable hydration of the preovulatory oocyte has ever been reported in rainbow trout (Oncorhynchus mykiss). In the present study, oocyte water content and dry mass were monitored using consecutive samples taken in vivo from the same female rainbow trout, from 4-5·days prior to ovulation to up to 7·days postovulation. In addition, yolk protein electrophoretic patterns were compared between oocytes sampled prior to germinal vesicle breakdown (GVBD) and unfertilized eggs. Furthermore, the effect of the maturation-inducing steroid (17,20␤ ␤-dihydroxy-4-pregnen-3-one, 17,20␤ ␤-P), cortisol and 11-deoxycorticosterone (DOC) on oocyte dry and wet masses, as well as GVBD occurrence was assessed in vitro. Finally, mRNA expression profiles of glucocorticoid and mineralocorticoid receptors as well as 11␤ ␤-hydroxysteroid dehydrogenase (11␤ ␤-HSD) were monitored in the periovulatory ovary by real-time PCR.Both in vivo and in vitro data showed, for the first time in rainbow trout, that a significant oocyte hydration occurs during oocyte maturation. In addition, an intra-oocyte dry matter increase was reported in vivo during the periovulatory period. However, yolk protein migration patterns were similar in preGVBD oocytes and unfertilized eggs, suggesting that no or little yolk proteolysis occurs during oocyte maturation. We also showed that oocyte hydration can be induced in vitro by 17,20␤ ␤-P and cortisol but not by DOC. In contrast, GVBD was only observed after 17,20␤ ␤-P stimulation. Finally, real-time PCR analysis showed an up-regulation of 11␤ ␤-HSD and glucocorticoid receptor 2 transcripts in the ovary at the time of oocyte maturation. Together, these results suggest that cortisol could participate in the control of oocyte hydration and possibly in other periovulatory ovarian functions.

“…Nevertheless, specific knockdown of AaAQP2 through RNAi, although significantly decreasing the corresponding transcript levels, did not give any noticeable phenotype (Drake et al, 2010). In teleosts, a functional AQP1-related water channel has been described in oocytes where it plays a role during oocyte hydration prior to ovulation (Fabra et al, 2005;Zapater et al, 2011). During vitellogenesis, basal oocytes of B. germanica increase in size exponentially as a result of the incorporation of yolk precursors and water (Belles et al, 1987;Ciudad et al, 2006;Martín et al, 1995), and AQPs may be involved in oocyte water balance during this process.…”

Section: A Herraiz and Othersmentioning

confidence: 99%

Identification and functional characterization of an ovarian aquaporin from the cockroachBlattella germanicaL. (Dictyoptera, Blattellidae)

Herraiz

Chauvigné

Cerdà

et al. 2011

SUMMARYAquaporins (AQPs) are membrane proteins that form water channels, allowing rapid movement of water across cell membranes. AQPs have been reported in species of all life kingdoms and in almost all tissues, but little is known about them in insects. Our purpose was to explore the occurrence of AQPs in the ovary of the phylogenetically basal insect Blattella germanica (L.) and to study their possible role in fluid homeostasis during oogenesis. We isolated an ovarian AQP from B. germanica (BgAQP) that has a deduced amino acid sequence showing six potential transmembrane domains, two NPA motifs and an ar/R constriction region, which are typical features of the AQP family. Phylogenetic analyses indicated that BgAQP belongs to the PRIP group of insect AQPs, previously suggested to be water specific. However, ectopic expression of BgAQP in Xenopus laevis oocytes demonstrated that this AQP transports water and modest amounts of urea, but not glycerol, which suggests that the PRIP group of insect AQPs may have heterogeneous solute preferences. BgAQP was shown to be highly expressed in the ovary, followed by the fat body and muscle tissues, but water stress did not significantly modify the ovarian expression levels. RNA interference (RNAi) reduced BgAQP mRNA levels in the ovary but the oocytes developed normally. The absence of an apparent ovarian phenotype after BgAQP RNAi suggests that other functionally redundant AQPs that were not silenced in our experiments might exist in the ovary of B. germanica. Supplementary material available online at