Wong Marty Kwok-Shing, Pipil Supriya, Kato Akira, Takei Yoshio
Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba, Japan.
Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba, Japan.
Comp Biochem Physiol A Mol Integr Physiol. 2016 Sep;199:130-141. doi: 10.1016/j.cbpa.2016.06.018. Epub 2016 Jun 17.
Two cystic fibrosis transmembrane conductance regulator (CFTR) isoforms, CFTRa and CFTRb, were cloned in Japanese eel and their structures and functions were studied in different osmoregulatory tissues in freshwater (FW) and seawater (SW) eels. Molecular phylogenetic results suggested that the CFTR duplication in eels occurred independently of the duplication event in salmonid. CFTRa was expressed in the intestine and kidney and downregulated in both tissues in SW eels, while CFTRb was specifically expressed in the gill and greatly upregulated in SW eels. Structurally, the CFTR isoforms are similar in most functional domains except the regulatory R domain, where the R domain of CFTRa is similar to that of human CFTR but the R domain of CFTRb is unique in having high intrinsic negative charges and fewer phosphorylation sites, suggesting divergence of isoforms in terms of gating properties and hormonal regulation. Immunohistochemical results showed that CFTR was localized on the apical regions of SW ionocytes, suggesting a Cl(-) secretory role as in other teleosts. In intestine and kidney, however, immunoreactive CFTR was mostly found in the cytosolic vesicles in FW eels, indicating that Cl(-) channel activity could be low at basal conditions, but could be rapidly increased by membrane insertion of the stored channels. Guanylin (GN), a known hormone that increases CFTR activity in mammalian intestine, failed to redistribute CFTR and to affect its expression in eel intestine. The results suggested that GN-independent CFTR regulation is present in eel intestine and kidney.
在日本鳗鲡中克隆出了两种囊性纤维化跨膜传导调节因子（CFTR）亚型，即CFTRa和CFTRb，并在淡水（FW）和海水（SW）鳗鲡的不同渗透调节组织中研究了它们的结构和功能。分子系统发育结果表明，鳗鲡中的CFTR复制独立于鲑科鱼类中的复制事件发生。CFTRa在肠道和肾脏中表达，在SW鳗鲡的这两种组织中均下调，而CFTRb特异性表达于鳃中，且在SW鳗鲡中大幅上调。在结构上，除了调节性R结构域外，CFTR亚型在大多数功能域中相似，其中CFTRa的R结构域与人CFTR的R结构域相似，但CFTRb的R结构域具有独特的高固有负电荷和较少的磷酸化位点，这表明亚型在门控特性和激素调节方面存在差异。免疫组织化学结果表明，CFTR定位于SW离子细胞的顶端区域，表明其具有与其他硬骨鱼一样的Cl(-)分泌作用。然而，在肠道和肾脏中，免疫反应性CFTR在FW鳗鲡的胞质囊泡中大多被发现，这表明在基础条件下Cl(-)通道活性可能较低，但通过储存通道的膜插入可使其迅速增加。鸟苷林（GN）是一种已知的可增加哺乳动物肠道中CFTR活性的激素，它未能使CFTR重新分布，也未影响其在鳗鲡肠道中的表达。结果表明，鳗鲡肠道和肾脏中存在不依赖GN的CFTR调节。
