海水酸化對海水青鱂魚表皮上催產素受器和腺苷酸環化酶的影響

Abstract

大氣中二氧化碳濃度的提升，是導致目前「海洋酸化」的主因，酸化海水對於水生動物的衝擊更是亟待研究的全球議題。過去許多研究已發現：二氧化碳溶入導致的海水酸化，對於眾多現存的海洋生物會造成負面影響。然而，酸化海水對於海洋硬骨魚的激素反應，以及連帶的腺苷酸環化酶調控路徑的影響研究，依舊是付之闕如。 本研究發現：在酸化海水(pH 7.6)環境中，海水青鱂魚的催產素受器isotocin receptor (ITR2)與腺苷酸環化酶adenylyl cyclase (ADCY5)於胚胎和成魚鰓上的基因表現量，相較於控制組(pH 8.1)皆顯著上升。藉由螢光原位雜合與免疫細胞化學染色實驗發現：ITR2與ADCY5分別表現於胚胎表皮與成魚鰓上離子細胞的底側膜與頂膜。此外，將受精卵的ITR2與ADCY5同時進行基因轉譯弱化，再轉移至酸化環境馴養後發現：卵黃囊的排酸量會顯著減少，此生理表徵與表皮細胞排酸相關離子通道蛋白的表現受到抑制有關。根據以上實驗結果推論：硬骨魚類會藉由活化表皮上G蛋白偶合相關之激素受器(ITR2)，引發腺苷酸環化酶(ADCY5)的作用，進而誘導訊息調控路徑下游離子通道的運作，以有效控制動物體內的酸鹼平衡，來對抗海水酸化造成的生物壓力。

Seawater acidification, a prior environmental perturbation, is resulted from accelerating seawater pCO2 levels due to the anthropogenic CO2 emissions. Various negative effects were proved in the living marine organisms by serious of hypercapnic-treated estimations. However, the physiological machinery regarding hormone response associates with adenylyl cyclases signaling pathways is still unclear in marine teleosts under acidic stress. In this study, marine medaka (Oryzias melastigma) was utilized to explore the effects of CO2-induced acidified seawater on the above responses. On one hand, isotocin receptor homolog (ITR2) was thought to be involved in differentiation and proliferation of epithelial ionocytes. In pH 7.6 treatment group, the transcriptional levels of ITR2 were up-regulated in the larvae and adult gills compared with the control (pH 8.1) counterpart. On the other hands, adenylyl cyclase isoform (ADCY5), an enzyme which can induce downstream ion-transport while catalyzes by the G protein-coupled receptors. In pH 7.6 treatment group, the transcriptional levels of ADCY5 in larvae increased significantly compared with the control (pH 8.1) ones. Moreover, ITR2 and ADCY5 were found to be localized predominantly on the basolateral and apical membrane of epithelium ionocytes, respectively, in adult gills and larval yolk sac. Furthermore, while the ITR2 and ADCY5 were both abolished, ionocyte-related transporters were downregulated, thus the proton secretion from the yolk sac skin was decreased significantly under pH 7.6 acidic condition. Consequently, epithelial ITR2 and ADCY5 play essential roles in acid-base homeostasis under acidic perturbations.