Trial lecture title: The roles of non-coding RNAs in fish development.
The ordinary opponents are:
- First opponent: Professor Samuel A. Martin, University of Aberdeen, Scotland
- Second opponent: Associate Professor Trine Ballestad Rounge, University of Oslo
- Leader of the committee: Head of Studies Hege Tunsjø, OsloMet
The leader of the public defence is Associate Professor Ole Herman Ambur, OsloMet.
The main supervisor is Professor Rune Andreasen, OsloMet. The co-supervisor is Senior Scientist Tone-Kari Knutsdatter, Norwegian Food Research Institute (Nofima).
Thesis abstract
Background
Smoltification, or parr-smolt transformation, is a complex pre-adaptive process of behavioral, developmental, biochemical, and physiological changes that transforms an Atlantic salmon parr living in freshwater (FW) into a seawater (SW)-ready smolt.
Successful smoltification is crucial for long-term adaptation to SW, survival, and growth in the sea. In contrast, suboptimal smoltification contributes to higher mortality in the SW phase and increases the risk of poor development, growth, and health.
Suboptimal smoltification remains a challenge for Atlantic salmon production in Norway, leading to substantial economic losses. MicroRNAs (miRNAs) are important post-transcriptional regulators of gene expression that play critical roles in various biological processes.
The aim of this project was to investigate whether any Atlantic salmon miRNAs are involved in the regulation of smoltification and seawater adaptation (SWA), and to reveal biological processes that are likely controlled by these particular miRNAs.
About the project
High-throughput sequencing of small RNAs in three key organs (head kidney, liver, and gill) of Atlantic salmon was used to characterize changes in miRNA expression associated with smoltification and SW adaptation.
This revealed 62, 54, and 18 miRNAs that were differentially expressed (DE) in liver, head kidney, and gill, respectively. Further investigations indicated that these likely are biologically important guide miRNAs (gDE-miRNAs).
Microarray analyses of same materials revealed 5708, 2709, and 2382 mRNAs as differentially expressed in liver, head kidney and gill, respectively. Among these, 2804, 1827, and 747 DE-mRNAs were predicted to be miRNA targets of the gDE-miRNAs in liver, head kidney, and gills, respectively.
Gene enrichment analysis of negatively correlated miRNA-mRNA interactions in head kidney showed that they were enriched in important biological processes such as hormone synthesis, stress response, immune response, and ion transport.
Furthermore, gene enrichment of DE-miRNA targets in the liver and gills also revealed several enriched biological processes that likely involve post-transcriptional control by the gDE-miRNAs. These include carbohydrate and lipid biosynthesis, amino acid and steroid metabolism, protein transport, response to external stimuli, the immune system, and extracellular organization.
Critical genes important in smoltification, such as Cytochrome P4501A (cyp1a1), Na+, K+-ATPase subunits (nkaα1a, nkaα1b and nkaβ), ion transporter cftr1 and aquaporin subunit (aqp11), were among the predicted targets in gill.
Collectively, these results indicate that the characterized gDE-miRNAs are essential post-transcriptional regulators that help FW-adapted parr successfully develop into SW-adapted smolts. The identification of gDE-miRNAs opens up for exploring these miRNAs as biomarkers. The altered expression of such gDE-miRNAs may potentially predict the smoltification status more precisely than the currently used biomarkers.
The predicted miRNA targets revealed here need to be verified experimentally, and the gDE-miRNAs and their target genes need to be further studied to reveal the molecular details of this post-transcriptional regulation.
