Claudin-10isoform expression and cation selectivity change with salinity in salt-secreting epithelia ofF. heteroclitus

Abstract

To provide insight into claudin (Cldn) tight junction (TJ) protein contributions to branchial salt secretion in marine teleost fishes, this study examined TJ protein isoforms of a euryhaline teleost (mummichog;) in association with salinity change and measurements of transepithelial cation selectivity. Mummichogs were transferred from freshwater (FW) to seawater (SW, 35‰) and from SW to hypersaline SW (2SW, 60‰) in a time course with transfer control groups (FW to FW, and SW to SW). FW to SW transfer increased mRNA abundance of and twofold, whilst and transcripts were unchanged. Transfer from SW to 2SW did not alter , and transiently altered abundance, but increased and fourfold. This was coincident with an increased number of single-stranded junctions (observed by transmission electron microscopy). For both salinity transfers, (1) mRNA was acutely responsive (i.e. after 24 h), (2) other responsive isoforms increased later (3-7 days), and (3) cystic fibrosis transmembrane conductance regulator () mRNA was elevated in accordance with established changes in transcellular Cl movement. Changes in mRNA encoding and appeared linked, consistent with the tandem repeat locus in the genome, whereas mRNA for tandem and seemed independent of each other. Cation selectivity sequence measured by voltage and conductance responses to artificial SW revealed Eisenman sequence VII: Na>K>Rb∼Cs>Li Collectively, these data support the idea that Cldn-10 TJ proteins create and maintain cation-selective pore junctions in salt-secreting tissues of teleost fishes.

Chromosome‐level genome assembly for the largemouth bass Micropterus salmoides provides insights into adaptation to fresh and brackish water

“…Claudins are a family of transmembrane proteins and important components of tight junctions between cells. They tightly join the membranes of adjacent cells to prevent the flow of molecules across the intercellular space into cell, thereby regulating the extent of tight junctions between cells and the permeability to water and solutes (Baltzegar et al., 2013; Marshall et al., 2018; Mineta et al., 2011). Tight junctions also close or seal the space between cells and thus set up a semipermeable barrier to prevent or reduce paracellular diffusion (“barrier function”; Findley & Koval, 2009).…”

Population transcriptomics reveals weak parallel genetic basis in repeated marine and freshwater divergence in nine‐spined sticklebacks

“…Claudins are tight junction membrane proteins that are expressed in epithelia and endothelia, and form paracellular barriers and pores that determine tight junction permeability (Gunzel & Yu, 2013). Earlier studies indicate that expression variation in claudins is important in permeability changes associated with salinity acclimation and possibly the formation of deeper tight junctions in the gills of freshwater fish (Bagherie‐Lachidan, Wright, & Kelly, 2008; Kolosov, Bui, Chasiotis, & Kelly, 2013; Madsen & Tipsmark, 2008; Marshall et al., 2018; Tipsmark, Baltzegar, Ozden, Grubb, & Borski, 2008; Tipsmark et al., 2016). Our results suggest that both expression changes and genetic variation in CLDND1 might play a key role in the repeated marine‐freshwater divergence in nine‐spined sticklebacks.…”

Draft genome assembly of Tenualosa ilisha, Hilsa shad, provides resource for osmoregulation studies

“…The presence of multiple claudins in T. ilisha (68) exceeds the number of previously reported in European seabass (61), stickleback (57), tilapia (56), fugu (56), zebrafish (54), medaka (48) and Atlantic cod (47) 11,15,84 . Role of isoforms of Claudin 6, 8, 10, 15 and 27 have been reported for acclimation to freshwater and seawater adaptation in fish 85–88 . Orthology analysis of specific osmo-regulatory genes revealed a variant of Claudin in T. ilisha , CLDZ gene with two copies, which has been reported to be responsive to nociceptive events in fish 89 .…”