Mummichogs (Fundulus heteroclitus) can tolerate abrupt changes in environmental salinity because of their ability to rapidly adjust the activities of ionocytes in branchial and opercular epithelia. In turn, the concerted expression of sub-cellular effectors of ion transport underlies adaptive responses to fluctuating salinities. Exposure to seawater (SW) stimulates the expression of Na+/K+/2Cl− cotransporter 1 (nkcc1) and cystic fibrosis transmembrane regulator (cftr) mRNAs in support of ion extrusion by SW-type ionocytes. Given the incomplete understanding of how freshwater (FW)-type ionocytes actually operate in mummichogs, the transcriptional responses essential for ion absorption in FW environments remain unresolved. In a subset of species, a ‘fish-specific’ Na+/Cl− cotransporter denoted Ncc2 (Slc12a10) is responsible for the uptake of Na+ and Cl− across the apical surface of FW-type ionocytes. In the current study, we identified an ncc2 transcript that is highly expressed in gill filaments and opercular epithelium of FW-acclimated mummichogs. Within 1 day of transfer from SW to FW, ncc2 levels in both tissues increased in parallel with reductions in nkcc1 and cftr. Conversely, mummichogs transferred from FW to SW exhibited marked reductions in ncc2 concurrent with increases in nkcc1 and cftr. Immunohistochemical analyses employing a homologous antibody revealed apical Ncc2-immunoreactivity in Na+/K+-ATPase-immunoreactive ionocytes of FW-acclimated animals. Our combined observations suggest that Ncc2/ncc2-expressing ionocytes support the capacity of mummichogs to inhabit FW environments.

中文翻译：

---

ncc2 在 mummichog 鳃盖上皮和鳃中的盐度依赖性表达 (Fundulus heteroclitus)

Mummichogs (Fundulus Heteroclitus) 可以耐受环境盐度的突然变化，因为它们能够快速调整鳃和鳃盖上皮细胞中离子细胞的活性。反过来，离子转运亚细胞效应物的协同表达是对盐度波动的适应性反应的基础。暴露于海水 (SW) 会刺激 Na+/K+/2Cl− 协同转运蛋白 1 (nkcc1) 和囊性纤维化跨膜调节因子 (cftr) mRNA 的表达，以支持 SW 型离子细胞的离子挤出。鉴于对淡水 (FW) 型离子细胞在木乃伊猪中的实际运作方式尚不完全了解，FW 环境中离子吸收所必需的转录反应仍未得到解决。在一个物种子集中，表示为 Ncc2 (Slc12a10) 的“鱼类特异性”Na+/Cl- 协同转运蛋白负责在 FW 型离子细胞的顶端表面摄取 Na+ 和 Cl-。在目前的研究中，我们确定了一个 ncc2 转录物，它在 FW 驯化的木乃伊猪的鳃丝和鳃盖上皮中高度表达。在从 SW 转移到 FW 的 1 天内，两种组织中的 ncc2 水平都随着 nkcc1 和 cftr 的减少而增加。相反，从 FW 转移到 SW 的木乃伊猪表现出 ncc2 显着减少，同时 nkcc1 和 cftr 增加。采用同源抗体的免疫组织化学分析揭示了 FW 驯化动物的 Na+/K+-ATPase 免疫反应性离子细胞的顶端 Ncc2 免疫反应性。