類雌激素受體在青鱂魚離子調控之角色

The role of estrogen-related receptors in ion regulation of medaka (Oryzias melastigma)

施尚武(Shang-Wu Shih)

指導教授 ： 黃鵬鵬

國立臺灣大學/生命科學院/漁業科學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201901567

摘要

廣鹽性硬骨魚類能夠生存在廣泛的鹽度範圍內，包含淡水及海水。成魚的鰓或胚胎表皮上的離子細胞是富含粒線體的特化細胞，能夠表現不同的離子運輸蛋白來運輸離子。這些細胞在淡水中負責吸收離子，在海水中則負責排出離子，藉此來維持體內體液的離子組成。先前研究已經提出了在廣鹽性青鱂魚中淡水型離子細胞和海水型離子細胞的模型，但仍無法完整解釋其離子調節的詳細機制。因此，發掘可能參與離子調控的因子是一項非常重要且有助於全面了解魚類如何適應變動環境的議題。類雌激素受體(ERR)是一種孤兒核受體，能夠作為轉錄因子來調控其他基因的表現，包括與能量代謝有關的基因。過去研究顯示，哺乳類的ERRα和ERRγ可以調控離子運輸蛋白的表現，暗示ERR家族可能參與離子的調控。因此，本研究使用印度種青鱂魚作為實驗物種來探討ERR家族在魚類離子調控中所扮演的角色。在將青鱂魚成魚及胚胎從淡水轉移到海水過後，ERRα、ERRβ1、ERRγ1和 ERRγ2在胚胎及成魚鰓的基因表現量皆顯著下降，表示ERR家族對青鱂魚在淡水的適應可能非常重要。接著，在原位雜交及免疫組織化學染色的結果指出，不論在成魚的鰓或是胚胎的表皮上，ERRγ2的mRNA表現大部分都和鈉鉀離子幫浦的蛋白質表現位置相同，表示ERRγ2會表現在大部分的離子細胞中。此外，弱化胚胎ERRγ2的表現會造成體內鈉、氯離子的含量降低，同時也降低離子細胞對鈉離子吸收的速率，但卻不影響胚胎表皮離子細胞的數目、耗氧及排銨速率。總結而言，本研究認為表現在離子細胞上的ERRγ2可能會參與鹽類的吸收機制，以利青鱂魚適應淡水。然而，ERRγ2如何調控離子細胞吸收鹽類的詳細機制尚不清楚，仍需在未來研究中更進一步釐清。

關鍵字

類雌激素受體 ； 離子調控 ； 鹽類吸收 ； 離子細胞 ； 青?魚

並列摘要

Euryhaline teleosts are capable of surviving within a wide range of salinities including in freshwater (FW) and seawater (SW). Ionocytes in fish gills or embryonic skin are specialized mitochondrion-rich cells which express different ion transporters to transport ions. These cells are responsible for ion absorption and secretion to maintain ion compositions of body fluids in FW and SW, respectively. The basic regulatory model of FW and SW types of ionocytes in medaka has been proposed, but the detailed ionoregulatory mechanisms are still not explained well. Thus, discovering possible factors involved in ion regulation is an important issue and is helpful to completely understand how fishes acclimate to fluctuating environments. Estrogen-related receptors (ERRs), steroid hormone receptors, are orphan nuclear receptors, functioning as transcription factors to regulate the expression of other genes, including energy metabolism-related genes. Previous studies showed that ERRα and ERRγ regulate the expression of ion transporters in mammals, implying that ERRs might involve in ion regulation. Therefore, this study used Indian medaka (Oryzias melastigma), euryhaline teleosts, as experimental organisms to investigate the role of ERRs in ion regulation of fishes. The mRNA expression of errα, errβ1, errγ1, and errγ2 in medaka embryos and adult gills were down-regulated after transfer from FW to SW, suggesting that ERRs may play roles in acclimation to FW. Besides, the results of in situ hybridization showed the mRNA signals of errγ2 were mostly co-localized with the immunohistochemistry signals of ionocyte marker, Na+-K+ ATPase (NKA), in both embryos and adult gills in FW, indicating that most part of ERRγ2 is expressed in the ionocyte. Moreover, ERRγ2 knockdown in embryos reduced the Na+/Cl- contents and Na+ influxes of ionocytes, but did not affect the ionocyte numbers in the embryonic skin, O2 consumption rate, and NH4+ secretion rate in the embryos. Overall, the present study suggested that ERRγ2 expressed in ionocytes may participate in salt-absorption mechanisms to adapt to FW. However, how ERRγ2 regulates the salt-absorption of ionocytes is still unclear and will be further investigated in the future.

並列關鍵字

estrogen-related receptor ； ion regulation ； salt absorption ； ionocyte ； medaka

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