Iron–sulfur cluster scaffold (ISCU) gene is duplicated in salmonid fish and tissue and temperature dependent expressed in rainbow trout

The iron–sulfur cluster protein ISCU is a scaffold protein tasked with the building and mediation of iron–sulfur [Fe–S]-clusters. These are crucial for [Fe–S]-enzymes, which are involved in essential biological cell processes like metabolism or ion transport. Analysis of ISCU in rainbow trout (Oncorhynchus mykiss) and maraena whitefish (Coregonus maraena) revealed the existence of two gene variants in each of the two salmonids. This study presents the characterization of the duplicated ISCU cDNA sequences in both species as well as the comparative functional analysis of the genes in healthy and affected fish of two rainbow trout strains differing in trait robustness under regional aquaculture conditions. Coding sequences of trout ISCUA and ISCUB genes are spanning over five exons. Open reading frames (ORF) of trout (ISCUA: 495 bp, ISCUB: 498 bp) and whitefish (ISCUA and ISCUB: 495 bp) genes encode for evolutionary highly conserved proteins and share 72% sequence similarity with human ISCU.Transcriptome analyses comparing healthy fish of the local rainbow trout strain BORN and the import strain TCO revealed strain-specific expression patterns for ISCU. Expression analyses by quantitative RT-PCR indicated remarkable differences between the transcript level of the gene variants ISCUA and ISCUB. Moderate temperature challenge (8 °C and 23 °C) suggests a generally higher transcript level of the two gene variants at 8 °C in the liver, spleen, and gill of both strains. However, no remarkable differences between the strains occurred in the temperature-dependent ISCU gene expression profiles. The experimental infection with Aeromonas salmonicida resulted in a different ISCU gene expression in the gill and trunk kidney of both strains after two weeks, suggesting a specific role of the scaffold gene in rainbow trout strain BORN, regarding the recovery after infection. Although results partially reflect the expected strain- and tissue-specific ISCUA and ISCUB regulation in rainbow trout, the data do not support the assumed association of ISCU with the trait robustness.

► ISCU gene is duplicated in rainbow trout and maraena whitefish.
► Sequence and evolutionary conservation of ISCUA and ISCUB genes were determined.
► ISCUA and B gene expression profiles are tissue specific in rainbow trout.
► ISCU gene expression in rainbow trout is temperature-dependent.
► An infection-dependent expression of ISCUA and B in rainbow trout was not confirmed.