Abstract
Salmon farming is a key industry in Norway, with a yearly production of more than 1,2 million tons. However, sustainability concerns are currently hampering further expansion of the industry. A long-term negative environmental effect is the genetic introgression from escaped farmed salmon into wild populations. Reduced fish welfare associated with precocious maturity represents another obstacle, since robust farmed fish is needed to avoid negative stress phenotypes associated with sexual maturation, such as cataract, bone and fin deformities, higher disease susceptibility, and osmoregulatory problems.
In the recent years, the field of gene editing has made substantial advances due to the introduction of CRISPR/Cas9, a highly efficient and potent methodology. CRISPR/Cas9 allows editing of specific DNA sequences in any organism, which opens for new possibilities to edit key genetic traits in aquaculture. Using CRISPR/Cas9 allows gene editing at different levels and does not necessarily involve transgenesis, which has been the major focus for the criticism towards genetically modified organisms. With CRISPR/Cas9 it is possible to perform cisgenic editing, which does not introduce any “foreign” DNA to the organism, but instead induces changes in its existing genome sequence, which is different from traditional technologies used to edit genomes.
We have established a protocol for gene knock out, and we are currently exploring ways to perform gene knock in, by CRISPR/Cas9 in Atlantic salmon. This in combination with the sequencing of the Atlantic salmon genome allows starting a new era of improved breeding in salmonid aquaculture. Respective studies should aim at elucidating how (mono- and polygenic) traits influence for example disease resistance, reproduction, or welfare, and ultimately if and how gene edited fish can be used in aquaculture to solve major environmental bottlenecks in the production of salmon (e.g. to mitigate problems with escaped fish and diseases).
A first prerequisite for the introduction of gene edited fish to sea cage farming is sterility, to avoid any chances of genetic introgression of escapees with wild salmon populations. Therefore, we have explored the possibility to produce salmon devoid of germ cells, and thus is 100% sterile. This has been successful using CRISPR/Cas9 to knock out one single gene, dead end (dnd). Furthermore, our germ cell-free salmon shows no signs of entering puberty, which is different from the sterile triploid salmon that is currently being tested for large scale production in some salmon farms. Nevertheless, since germ cell-free broodstock cannot reproduce, we do not yet have an efficient way to produce these fishes. We are currently working on ideas on how to solve this.
Another path to control the timing of reproduction and reduce genetic introgression is to use salmon predetermined to mature late. If escaping, late maturing salmon are more likely to die before reaching the spawning grounds for wild populations. We have identified a region in the salmon genome largely controlling the age at puberty onset. Current projects are using CRISPR to identify the causative mutation both by knock out of genes in the region and by homologous recombination experiments (of putatively causative nonsynonymous SNPs) using clonal lines with either genotypes for the late and early maturation alleles.
In summary, gene editing is not only an important tool for understanding salmon biology, but we also foresee that the potential improvements considering sustainability issues may result the future use of gene edited fish in aquaculture.
In the recent years, the field of gene editing has made substantial advances due to the introduction of CRISPR/Cas9, a highly efficient and potent methodology. CRISPR/Cas9 allows editing of specific DNA sequences in any organism, which opens for new possibilities to edit key genetic traits in aquaculture. Using CRISPR/Cas9 allows gene editing at different levels and does not necessarily involve transgenesis, which has been the major focus for the criticism towards genetically modified organisms. With CRISPR/Cas9 it is possible to perform cisgenic editing, which does not introduce any “foreign” DNA to the organism, but instead induces changes in its existing genome sequence, which is different from traditional technologies used to edit genomes.
We have established a protocol for gene knock out, and we are currently exploring ways to perform gene knock in, by CRISPR/Cas9 in Atlantic salmon. This in combination with the sequencing of the Atlantic salmon genome allows starting a new era of improved breeding in salmonid aquaculture. Respective studies should aim at elucidating how (mono- and polygenic) traits influence for example disease resistance, reproduction, or welfare, and ultimately if and how gene edited fish can be used in aquaculture to solve major environmental bottlenecks in the production of salmon (e.g. to mitigate problems with escaped fish and diseases).
A first prerequisite for the introduction of gene edited fish to sea cage farming is sterility, to avoid any chances of genetic introgression of escapees with wild salmon populations. Therefore, we have explored the possibility to produce salmon devoid of germ cells, and thus is 100% sterile. This has been successful using CRISPR/Cas9 to knock out one single gene, dead end (dnd). Furthermore, our germ cell-free salmon shows no signs of entering puberty, which is different from the sterile triploid salmon that is currently being tested for large scale production in some salmon farms. Nevertheless, since germ cell-free broodstock cannot reproduce, we do not yet have an efficient way to produce these fishes. We are currently working on ideas on how to solve this.
Another path to control the timing of reproduction and reduce genetic introgression is to use salmon predetermined to mature late. If escaping, late maturing salmon are more likely to die before reaching the spawning grounds for wild populations. We have identified a region in the salmon genome largely controlling the age at puberty onset. Current projects are using CRISPR to identify the causative mutation both by knock out of genes in the region and by homologous recombination experiments (of putatively causative nonsynonymous SNPs) using clonal lines with either genotypes for the late and early maturation alleles.
In summary, gene editing is not only an important tool for understanding salmon biology, but we also foresee that the potential improvements considering sustainability issues may result the future use of gene edited fish in aquaculture.