Activity: Talks and presentations › Talks and presentations in private or public companies
The Na+,K+-ATPase is a major driving force for ion transport in gill epithelial cells and changes in abundance, isoform composition and cellular localization is seen during the adaption to changes in salinity. We recently identified eight FXYD genes in the salmon transcriptome and QPCR analysis reveals a tissue dependent expression pattern. FXYD proteins appear to be involved in tissue specific regulation of the Na+,K+-ATPase in mammals, but the role in lower vertebrates is limited. We examined the expression of gill FXYD isoforms in salmon during acclimation to seawater (SW) and parr-smolt transformation, a “pre-adaptation” to SW prior to seaward migration in the spring to test if FXYD proteins may be involved in adjusting gill function during these important adaptations. Interestingly, a parallel increase in FXYD9 and FXYD11 levels with Na,K-ATPase abundance during parr-smolt transformation suggests that these auxillary subunits play a particular role in controlling catalytic rate in situ when the FW fish prepares for SW entry.
Another exiting new line of research in euryhaline teleosts, address the molecular base of permeability changes in gill epithelia that are essential during acclimation to changed salinity. Thus, we have examined expression patterns of branchial claudins, that are tight junction proteins and important determinants of ion selectivity and general permeability in epithelia. We identified 24 Atlantic salmon genes belonging to the claudin family by screening expressed sequence tag libraries available at NCBI. In gill libraries five isoforms (10e, 27, 28a, 28b and 30) were present and acclimation to SW reduced the expression of claudin 27 and claudin 30 but had no overall effect on claudin 28a and claudin 28b. In contrast, SW induced a 4-fold increase in expression of claudin 10e. In accord, a peak in branchial claudin 10e was observed during smoltification in May, coinciding with optimal SW tolerance. Smoltification induced no significant changes in expression of the other isoforms. This study demonstrates the expression of an array of salmon claudin isoforms and shows that SW acclimation involves inverse regulation, in the gill, of claudin 10e versus claudin 27 and 30. It is possible, that claudin 10e is an important component of cation selective channels while reduction in claudin 27 and 30 may change permeability conditions in favour of the ion secretory mode of the SW gill.