Abstract
The anadromous Atlantic salmon utilizes both fresh and salt water (FW and SW) habitats during its life cycle. The parr-smolt transformation (PST) is an important developmental transition from a FW adapted juvenile parr to a SW adapted smolt. Physiological changes in osmoregulatory tissues, particularly the gill, are key in maintaining effective ion regulation during PST. Changes are initiated prior to SW exposure (preparative phase), and are completed when smolts enter the sea (activational phase) where osmotic stress may directly stimulate changes in gene expression. In this paper we identify 4 nuclear factor of activated T cells (NFAT5, an osmotic stress transcription factor) paralogues in Atlantic salmon, which showed strong homology in characterized functional domains with those identified in other vertebrates. Two of the identified paralogues (NFAT5b1 and NFAT5b2) showed increased expression following transfer from FW to SW. This effect was largest in parr that were maintained under short day photoperiod, and showed the highest increases in chloride ion levels in response to SW exposure. The results of this study suggest that NFAT5 is involved in the osmotic stress response of Atlantic salmon.
Highlights
The Atlantic salmon is an anadromous species, spending the first one to three years of life in a freshwater (FW) environment before migrating downstream and out to sea for one or multiple winters before returning to its natal stream to spawn
Four nuclear factor of activated T-cells 5 (NFAT5) paralogous genes named NFAT5a1, NFAT5a2, NFAT5b1 and NFAT5b2 were identified in the Atlantic salmon genome version AGKD00000000.4: NFAT5a1 on chromosome ssa10 (AGKD04000113.1, 88550193..88575551, E = 4e−136), NFAT5a2 on chromosome ssa16 (AGKD04000076.1, 22037579..22059470, E = 5e−122), NFAT5b1 on chromosome ssa11 (AGKD04000127.1, 18800113..18865778, E = 6e−108) and NFAT5b2 on chromosome ssa26 (AGKD04000059.1, 19149934..19204506, E = 2e−94)
There is a highly conserved core of 5 exons which is 100% conserved in length and a highly variable 3′ region where little alignment is observed. 5′ exons are highly conserved in length with a few variations, as is the case with the exons between the core and variable regions
Summary
The Atlantic salmon is an anadromous species, spending the first one to three years of life in a freshwater (FW) environment before migrating downstream and out to sea for one or multiple winters before returning to its natal stream to spawn. A process termed the parr-smolt transformation (PST) facilitates this exploitation of FW and salt water (SW) environments. The pathways governing detection of environmental salinity via molecular osmotic sensors in teleosts is not clear, a number of candidate genes that may serve this function have been identified, including adenyl cyclase (Saran and Schaap, 2004) and calcium sensing receptor (CaSR) (Nearing et al, 2002). The expression of downstream target genes is assumed to be modulated by osmotically-regulated transcription
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