Natural Sciences and Science Education, National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore 637616, Republic of Singapore.
Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore 117543, Republic of Singapore.
Comp Biochem Physiol A Mol Integr Physiol. 2021 Mar;253:110853. doi: 10.1016/j.cbpa.2020.110853. Epub 2020 Nov 27.
The marble goby, Oxyeleotris marmorata, is a freshwater teleost, but can acclimate progressively to survive in seawater (salinity 30). As an obligatory air-breather, it can also survive long periods of emersion. Two isoforms of Na/K-ATPase (nka) α-subunit, nkaα1 and nkaα3, but not nkaα2, had been cloned from the gills of O. marmorata. The cDNA sequence of nkaα1 consisted of 3069 nucleotides, coding for 1023 amino acids (112.5 kDa), whereas nkaα3 consisted of 2976 nucleotides, coding for 992 amino acids (109.5 kDa). As only one form of branchial Nkaα1 was identified using molecular cloning in this study, O. marmorata lacks specific freshwater- and seawater-type Nkaα isoforms as demonstrated by some other euryhaline fish species. The nkaα1 transcript level was about 2.5-fold higher than that of nkaα3 in the gills of freshwater O. marmorata. During exposure to seawater, the branchial transcript level of nkaα1 increased significantly on day 1 (3.3-fold) and day 6 (2.6-fold). By contrast, the branchial transcript level of nkaα3 increased significantly on day 1 (2.6-fold), but not on day 6, of seawater exposure. Six days of exposure to seawater also led to significant increases in protein abundances of Nkaα1 (6.9-fold) and Nkaα3 (~2.8-fold) in the gills of O. marmorata. Hence, the mRNA and protein expressions of both nkaα1/Nkaα1 and nkaα3/Nkaα3 were up-regulated in O. marmorata during seawater acclimation. This could explain why V increases but K for Na and K remain unchanged in Nka extracted from the gills of O. marmorata acclimated to seawater as reported previously.
大理石胡瓜鱼，Oxyeleotris marmorata，是一种淡水硬骨鱼，但可以逐渐适应生存于海水中（盐度 30）。作为一种必需的空气呼吸器，它也可以在长时间的离水后存活。两种 Na/K-ATPase (nka) α 亚基同工型，nkaα1 和 nkaα3，但不是 nkaα2，已从大理石胡瓜鱼的鳃中克隆出来。nkaα1 的 cDNA 序列由 3069 个核苷酸组成，编码 1023 个氨基酸（112.5 kDa），而 nkaα3 由 2976 个核苷酸组成，编码 992 个氨基酸（109.5 kDa）。由于本研究中仅使用分子克隆鉴定了一种鳃部 Nkaα1 形式，因此大理石胡瓜鱼缺乏一些其他广盐鱼类所具有的特定淡水和海水型 nkaα 同工型。在淡水大理石胡瓜鱼的鳃中，nkaα1 的转录水平比 nkaα3 高约 2.5 倍。在暴露于海水中时，鳃部 nkaα1 的转录水平在第 1 天（3.3 倍）和第 6 天（2.6 倍）显著增加。相比之下，鳃部 nkaα3 的转录水平在第 1 天（2.6 倍）但不在第 6 天显著增加。暴露于海水 6 天后，O. marmorata 鳃中的 Nkaα1（6.9 倍）和 Nkaα3（~2.8 倍）蛋白丰度也显著增加。因此，在海水适应过程中，O. marmorata 中 nkaα1/Nkaα1 和 nkaα3/Nkaα3 的 mRNA 和蛋白表达均上调。这可以解释为什么以前报道的从适应海水的大理石胡瓜鱼鳃中提取的 Nka 中，V 增加而 Na 和 K 的 K 保持不变。
