# Effects of Hybridization and Triploidization on Transcription of Core Metabolic and Stress Response Genes in Rainbow Trout (Oncorhynchus mykiss) × Brook Trout (Salvelinus fontinalis) Hybrids—Preliminary Results

## TL;DR

This study explores how hybridization and triploidization affect gene expression related to metabolism and stress in trout hybrids, finding mixed results on growth and stress response.

## Contribution

The study provides preliminary insights into transcriptional changes in triploid hybrids of rainbow and brook trout, linking gene expression to growth and stress response.

## Key findings

- Most genes showed stable expression in triploid hybrids compared to diploid parents, with some upregulation in energy and protein synthesis genes.
- Triploid hybrids exhibited downregulation of Hsp90B1, suggesting altered stress response regulation.
- Upregulated genes in triploid hybrids did not translate into improved growth performance.

## Abstract

The transcriptomic effects of hybridization and triploidization were investigated in diploid and triploid rainbow trout, diploid brook trout, as well as triploid hybrids of rainbow trout and brook trout. The examined fish were reared under identical conditions for about two and a half years after hatching. Expression of ten genes involved in cellular respiration (Atp5bp, Slc25a5), mitochondrial functioning (Mrpl28, Micu2), ribosome biogenesis (Rpl24, Rps24), proteasome-mediated protein turnover (Derl1, Psmc2), and protein chaperoning (Hsp90B1, Pdia4) was studied in liver and muscle tissues. Most of the analyzed genes (Atp5bp, Slc25a5, Mrpl28, Micu2, Rpl24, Rps24, Derl1, and Psmc2) displayed comparable expression levels in the liver tissue across the examined triploid hybrids and diploid parental species, with stabilization of genes that were both positively and negatively compensated in the triploid rainbow trout. In turn, significant upregulation of Slc25a5, Derl1, Rps24, and Rpl24 genes, together with downregulation of Micu2 gene, was observed in the triploid rainbow trout liver and muscle, respectively. On the other hand, triploid hybrids showed marked transcriptional upregulation of genes primarily associated with energy metabolism and protein synthesis (Atp5pb, Slc25a5, Rpl24, Rps24, and Pdia4) relative to all the fish groups examined. Although protein-synthesis- and energy-related genes were upregulated in the muscles of triploid hybrids, the recorded growth performance data did not indicate clear evidence of growth heterosis (MPH = −14.3% for body weight; MPH = −0.4% for body length), suggesting that potential benefits of increased heterozygosity in this cross may not be fully reflected in enhanced growth. Three- to four-fold downregulation of the heat shock protein (Hsp90B1) gene was also observed in both tissues of triploid hybrids compared with purebred diploid and triploid trout, which may reflect potential maladaptive genomic effects commonly observed in distant salmonid crosses, suggesting altered stress-response regulation in the examined triploid hybrids.