Nuclear localisation of a fish-derived ice-binding protein and related transcriptional changes in Caenorhabditis elegans.

Ice-binding proteins (IBPs) are functional molecules that enable organisms to survive severe cold by binding specifically to ice crystals and suppressing their growth and recrystallisation. Although their primary role has traditionally been viewed as antifreeze activity, recent studies have suggested additional cell-protective functions, including possible effects on membrane stability. Heterologous expression of the fish type III IBP NfeIBP in Caenorhabditis elegans has previously been shown to increase tolerance to cold and freezing stress. However, the understanding of the intracellular localisation of IBPs in vivo and their effects on gene expression remains limited. Here, we examined the intracellular localisation and associated cellular effects of the fish-derived IBP variant NfeIBP6(A20I), which is known to confer strong cold tolerance in C. elegans. An NfeIBP6(A20I)-wrmScarlet fusion protein expressed in body wall muscle cells was detected in both cytoplasmic and nuclear regions and partially overlapped with the nuclear marker NLSsfGFP, indicating its presence within nuclear compartment. Expression of NfeIBP6(A20I) did not cause detectable abnormalities in the physiological traits examined. Transcriptomic analysis further revealed biased changes in gene expression, with substantially more downregulated genes than upregulated genes. The downregulated genes were significantly enriched in biological processes related to cuticle development and immune response. These findings indicate that NfeIBP6(A20I) exhibits previously unrecognised intracellular behaviour in C. elegans and suggest that the functional scope of IBPs may extend beyond their conventional role in ice binding.