Gerber Lucie, Lee Carol Eunmi, Grousset Evelyse, Blondeau-Bidet Eva, Boucheker Nesrine Boudour, Lorin-Nebel Catherine, Charmantier-Daures Mireille, Charmantier Guy
Physiol Biochem Zool. 2016 May-Jun;89(3):233-50. doi: 10.1086/686323. Epub 2016 Apr 14.
The copepod Eurytemora affinis has an unusually broad salinity range, as some populations have recently invaded freshwater habitats independently from their ancestral saline habitats. Prior studies have shown evolutionary shifts in ion transporter activity during freshwater invasions and localization of ion transporters in newly discovered "Crusalis organs" in the swimming legs. The goals of this study were to localize and quantify expression of ion transport enzymes V-type H(+)-ATPase (VHA) and Na(+)/K(+)-ATPase (NKA) in the swimming legs of E. affinis and determine the degree of involvement of each leg in ionic regulation. We confirmed the presence of two distinct types of ionocytes in the Crusalis organs. Both cell types expressed VHA and NKA, and in the freshwater population the location of VHA and NKA in ionocytes was, respectively, apical and basal. Quantification of in situ expression of NKA and VHA established the predominance of swimming leg pairs 3 and 4 in ion transport in both saline and freshwater populations. Increases in VHA expression in swimming legs 3 and 4 of the freshwater population (in fresh water) relative to the saline population (at 15 PSU) arose from an increase in the abundance of VHA per cell rather than an increase in the number of ionocytes. This result suggests a simple mechanism for increasing ion uptake in fresh water. In contrast, the decline in NKA expression in the freshwater population arose from a decrease in ionocyte area in legs 4, likely resulting from decreases in number or size of ionocytes containing NKA. Such results provide insights into mechanisms of ionic regulation for this species, with added insights into evolutionary mechanisms underlying physiological adaptation during habitat invasions.
桡足类的近亲真宽水蚤具有异常广泛的盐度范围，因为一些种群最近已从其祖先的咸水栖息地独立侵入淡水栖息地。先前的研究表明，在淡水入侵过程中离子转运蛋白活性发生了进化转变，并且在游泳足新发现的“Crusalis器官”中离子转运蛋白有定位。本研究的目的是定位和量化近亲真宽水蚤游泳足中离子转运酶V型H(+) -ATP酶（VHA）和Na(+)/K(+) -ATP酶（NKA）的表达，并确定每条腿在离子调节中的参与程度。我们证实了Crusalis器官中存在两种不同类型的离子细胞。两种细胞类型均表达VHA和NKA，在淡水种群中，VHA和NKA在离子细胞中的位置分别是顶端和基部。对NKA和VHA原位表达的定量分析确定了第3和第4对游泳足在咸水和淡水种群的离子转运中占主导地位。相对于咸水种群（在15 PSU），淡水种群（在淡水中）第3和第4对游泳足中VHA表达的增加是由于每个细胞中VHA丰度的增加，而不是离子细胞数量的增加。这一结果表明了一种在淡水中增加离子摄取的简单机制。相比之下，淡水种群中NKA表达的下降是由于第4条腿中离子细胞面积的减小，这可能是由于含有NKA的离子细胞数量或大小的减少所致。这些结果为该物种的离子调节机制提供了见解，也为栖息地入侵期间生理适应的进化机制提供了更多见解。
