Differential Gene Expression During Smoltification of Atlantic Salmon (Salmo salar L.): a First Large-Scale Microarray Study

Abstract

The life cycle of the Atlantic salmon (Salmo salar) involves a period of 1 to 3 years in freshwater followed by migration to the sea where the salmon undergoes rapid growth. In preparation for the marine environment, while still in freshwater, the salmon undergo a transformation from a freshwater dwelling parr to a saltwater adapted smolt, a process known as smoltification. The Atlantic salmon Transcriptome Analysis of Important Traits of Salmon/Salmon Genome Project (TRAITS/SGP) cDNA microarray was used to investigate how gene expression alters during smoltification. Genes differentially expressed during smoltification were identified by comparing gene expression profiles in smolt brain, gill, and kidney tissue samples with those of parr. Of the three tissues investigated, the number of differentially expressed genes was the greatest in gill. Many of the differentially expressed genes could be assigned to one of four main categories: growth, metabolism, oxygen transport, and osmoregulation. Quantitative polymerase chain reaction successfully confirmed the differential expression of seven of the upregulated genes. The TRAITS/SGP cDNA microarray was used to successfully demonstrate for the first time how gene expression mediates smoltification in the Atlantic salmon. Changes in gene expression observed in this study reflected the physiological and biochemical changes recorded by previous studies describing the parr-smolt transformation. This study significantly increases our knowledge of smoltification and will benefit future studies in this area of research.

Comparison of Gene Expression in the Gill of Salmon (Salmo salar) Smolts from Anadromous and Landlocked Populations

“…Mitochondrial genes involved in aerobic energy metabolism were up-regulated in smolts as expected on the basis of an increase in numbers and size of the mitochondria-rich chloride cells in the gill of the smolting Atlantic salmon (Langdon & Thorpe 1985). Similar up-regulation of mitochondrial genes and Na,K-ATPase between the parr and smolt phases of development has recently been reported for this species by Seear et al (2010). These changes suggest that mitochondrial activity and aerobic energy production reach their peak value in the smolt phase, and are significantly lower in both parrs and postsmolts.…”

“…Interestingly, genes encoding collagen were strongly up-regulated in the smolt phase as noted also by Seear et al (2010). Besides being a ubiquitous component of the intercellular matrix, collagen is an essential structural component of the pillar cells of the gill filaments.…”

“…Although several aspects of the parr-smolt transformation have been extensively examined, to our knowledge there are no high-throughput transcriptomic analyses of the parr-smolt transformation of landlocked and anadromous salmon populations (Vornanen et al 2009, Seear et al 2010. Therefore, the present study was designed to compare transcriptomes of the gill filaments of three different Atlantic salmon stocks that migrate from freshwater streams to a freshwater lake (Lake Saimaa, Finland), from the River Neva (Russia) to the brackish water of the Baltic Sea and from the Teno River (Finland/ Norway) to the full-strength seawater of the Arctic Ocean, respectively.…”

Physiological and genetic basis for variation in migratory behavior in the three-spined stickleback, Gasterosteus aculeatus

“…4b). Transcriptomic studies of salmon migration have been extensively conducted (Aubin-Horth et al 2005Giger et al 2006;Bernier et al 2008;Miller et al 2009Miller et al , 2011Seear et al 2010). Microarrays of G. aculeatus, which have been used to investigate the effects of endocrine disruptors (Geoghegan et al 2008;Williams et al 2009;Katsiadakia et al 2010), sex-biased gene expression (Leder et al 2010), the transcriptomic response to predators (Sanogo et al 2011), comparison of gill transcripts between anadromous and stream-resident forms (Kitano et al 2010), and comparison of testis transcripts between incipient species (Kitano et al 2011), are also useful for transcriptome analyses of divergent migratory forms of G. aculeatus at various migratory stages.…”

Current Advances in Functional Genomics in Aquaculture

“…Genetic traits essential for improving production in ish farming include traits for feed conversion ratio [172], robustness [173], maturation timing [174], cold tolerance [163,175], high temperature tolerance [176] and salinity tolerance. In anadromous species such as Atlantic salmon, genetic traits for smoltiication [177], migration and spawning timing [178] have been determined.…”