Biology subjects

Edvardsen, R. B.

Publications and source records attributed to Edvardsen, R. B..

7 recordsLinked to original sources

bioRxiv2026

Vgll3a promotes sexual maturation in male and female Atlantic salmon

The age at which Atlantic salmon reaches sexual maturity shows a strong hereditary component associated with the vgll3a locus. The role of Vgll3 in maturation has remained unknown in vertebrates until recently, when it has been linked to pleiotropic roles in killifish, both delaying male maturation and affecting lifespan by protecting against cancer. As Atlantic salmon has two vgll3 paralogs, where only vgll3a has been associated with sexual maturation, it may provide a suitable model for studying the maturation-specific function of vgll3, as the other paralog may buffer for pleiotropic roles of vgll3. To address this, we used CRISPR/Cas9 to generate fish highly mutated in the vgll3a gene. We monitored their maturation and crossed highly mutated crispants to generate two year-classes of complete loss-of-function. All groups were reared under environmental conditions triggering early maturation in one-year-old males. We found a clear difference in the proportion of sexually maturing or mature fish between the different genotypes: in all experiments significantly fewer vgll3a-/- males entered puberty and reached final maturation compared to vgll3a+/- and vgll3a+/+ males. Furthermore, loss of vgll3a resulted in lower frequencies of maturation also in females. We conclude that Vgll3a stimulates maturation and that its complete removal significantly reduced maturation rates in both sexes in Atlantic salmon. Our findings also identify vgll3a as the causative gene in the locus associated with age at sexual maturity. Together, our findings support a new role for Vgll3 in initiating puberty in vertebrates and identifying salmon as a promising model for functional studies regarding the timing of sexual maturation.

genomics↗

bioRxiv2021

Cardiac dysfunction affects eye development and vision by reducing supply of lipids in fish

Developing organisms are especially vulnerable to environmental stressors. We aimed to understand the underlying mechanisms of phenanthrene (Phe) and crude oil induced eye malformations. We exposed Atlantic haddock (Melanogrammus aeglefinus) embryos to a known L-type calcium channel blocker, nicardipine hydrochloride (Nic), and compared to early embryonic crude oil (Oil) and late embryonic Phe toxicity. All treatments lead to severe, eye, jaw and spinal deformities at early larval stages. At 3 days post hatching, larvae from all treatments and corresponding controls were dissected. Eyes, trunk, head and yolk sac were subjected to lipid profiling, and eyes were also subjected to transcriptomic profiling. Changes in lipid profiles and the transcriptome suggested that the dysfunctional and abnormal eyes in our treatments were due to both disruption of signaling pathways and insufficient supply of essential fatty acids and other nutrients form the yolk.

molecular biology↗

bioRxiv2021

The salmon louse genome: copepod features and parasitic adaptations.

Copepods encompass a range of ecological roles from parasites to phytoplankton grazers linking primary producers to higher trophic levels. Despite these important roles, copepod genome assemblies are scarce. Lepeophtheirus salmonis is an economically and ecologically important ectoparasitic copepod. We present the 695.4 Mbp L. salmonis genome assembly containing {approx}60% repetitive regions and 13081 annotated protein-coding genes. The genome comprises 14 autosomes and a ZZ-ZW sex chromosome system. Assembly assessment identified 92.4% of the expected arthropod genes. Transcriptomics validated annotation and revealed a marked shift in gene expression after host attachment, including downregulation of genes related to circadian rhythm coinciding with abandoning diurnal migration. The genome shows evolutionary signatures including loss of peroxisomes, numerous FNII domains, and an incomplete heme homeostasis pathway suggesting heme proteins to be obtained from the host. Despite large capacity to develop resistance against chemical treatments L. salmonis exhibits low numbers of many genes involved in detoxification.

genomics↗

bioRxiv2021

A refinement to gene editing in Atlantic salmon using asymmetrical oligonucleotide donors

Selective breeding programs in aquaculture are limited by the heritability of the trait and long generation time in most fish species. New breeding technology (NBT) using CRISPR/Cas9-induced homology directed repair (HDR) have the potential to expedite genetic improvement in aquaculture, but the method requires optimization. Here we show that asymmetrical oligonucleotide (ODN) donors induce highly efficient and precise edits in individual Atlantic salmon founder animals. We performed single nucleotide replacement (SNR) in dnd with up to 59.2% efficiency, and inserted FLAG elements into slc45a2 and dnd, with up to 36.7 % and 32.7% efficiency, respectively. We found HDR efficiency to be dependent on template concentration, but a trade-off with respect to toxicity was observed. Using this NBT in salmon we demonstrate that precise modification of the genome can be achieved in a single generation, allowing efficient introgression of favorable alleles and bypassing challenges associated with traditional selective breeding.

molecular biology↗

bioRxiv2020

Heterochiasmy facilitated the establishment of gsdf as a novel sex determining gene in Atlantic halibut

Atlantic Halibut (Hippoglossus hippoglossus) has a X/Y genetic sex determination system, but the sex determining factor is not known. We produced a high-quality genome assembly and identified parts of chromosome 13 as the Y chromosome due to sequence divergence between sexes and segregation of sex genotypes in pedigrees. Linkage analysis revealed that all chromosomes exhibit heterochiasmy, i.e. male- and female restricted meiotic recombination intervals (MRR/FRR). We show that FRR/MRR intervals differ in nucleotide diversity and repeat class content and that this is true also for other Pleuronectidae species. We further show that remnants of a Gypsy-like transposable element insertion on chr13 promotes early male specific expression of gonadal somatic cell derived factor (gsdf). Less than 4 MYA, this male-determining element evolved on an autosomal FRR segment featuring pre-existing male meiotic recombination barriers, thereby creating a Y chromosome. We propose that heterochiasmy may facilitate the evolution of genetic sex determination systems.

genomics↗

bioRxiv2020

Targeted mutagenesis of {triangleup}5 and {triangleup}6 fatty acyl desaturases induce multiplex-mutagenesis and lipogenesis in Atlantic salmon (Salmo salar)

With declining wild fish populations, farmed Atlantic salmon (Salmo salar) has gained popularity as a source for healthy long-chain highly unsaturated fatty acids (LC-HUFA) including 20:5n-3 and 22:6n-3. However, the introduction of plant-based oil in fish diets has reduced the content of these beneficial LC-HUFA. The capability of biosynthesis of LC-HUFAs depends on fatty acids supplied in diets and the genetic potential residing in the fish. Key proteins involved in LC-HUFA synthesis in salmon include fatty acid desaturases 2 (Fads2). In a recent study we used CRISPR/Cas9 to generate two F0 mutant strains of salmon, 1){Delta} 6abc/5Mt with mutations in{Delta} 5fads2, {Delta}6fads2-a, {Delta}6fads2-b and {Delta}6fads2-c genes, and 2){Delta} 6bcMt with mutations in{Delta} 6fads2-b and {Delta}6fads2-c genes. The CRISPR mutated salmon (crispants) had reduced levels of LC-HUFA and expression of targeted fads2 genes. In present study we apply whole transcriptome analysis on these fads2 crispants. Our purpose is to evaluate the genetic mosaicism in fads2 crispants and the effect these mutations had on other lipid metabolism pathways in fish. Both{Delta} 6abc/5Mt and{Delta} 6bcMt crispants demonstrated high percentage of indels within all intended target genes, though different indel types and percentage were observed between individuals. Skipping of a CRISPR-targeted exon was observed in{Delta} 6fads2-a gene of{Delta} 6abc/5Mt salmon. The{Delta} 6abc/5Mt fish also displayed several disruptive indels which resulted in over 100 differentially expressed genes (DEGs) enriched in lipid metabolism pathways in liver. This includes up-regulation of srebp1 genes as well as genes involved in fatty acid de-novo synthesis, fatty acid {beta}-oxidation and lipogenesis. Both elovl5 and elovl2 genes were not changed, suggesting that the genes were not targeted by Srebp1. The mutation of{Delta} 6bcMt surprisingly resulted in over 3000 DEGs which were enriched in factors encoding genes involved in mRNA regulation and stability.

molecular biology↗

bioRxiv2017

Genomic architecture of codfishes featured by expansions of innate immune genes and short tandem repeats

BackgroundIncreased availability of genome assemblies for non-model organisms has resulted in invaluable biological and genomic insight into numerous vertebrates including teleosts. The sequencing and assembly of the Atlantic cod (Gadus morhua) genome and the genomes of many of its relatives (Gadiformes) demonstrated a shared loss 100 million years ago of the major histocompatibility complex (MHC) II genes. The recent publication of an improved version of the Atlantic cod genome assembly reported an extreme density of tandem repeats compared to other vertebrate genome assemblies. Highly contiguous genome assemblies are needed to further investigate the unusual immune system of the Gadiformes, and the high density of tandem repeats in this group.\n\nResultsHere, we have sequenced and assembled the genome of haddock (Melanogrammus aeglefinus) - a relative of Atlantic cod - using a combination of PacBio and Illumina reads. Comparative analyses uncover that the haddock genome contains an even higher density of tandem repeats outside and within protein coding sequences than Atlantic cod. Further, both species show an elevated number of tandem repeats in genes mainly involved in signal transduction compared to other teleosts. An in-depth characterization of the immune gene repertoire demonstrates a substantial expansion of MCHI in Atlantic cod compared to haddock. In contrast, the Toll-like receptors show a similar pattern of gene losses and expansions. For another gene family associated with the innate immune system, the NOD-like receptors (NLRs), we find a large expansion common to all teleosts, with possible lineage-specific expansions in zebrafish, stickleback and the codfishes.\n\nConclusionsThe generation of a highly contiguous genome assembly of haddock revealed that the high density of short tandem repeats as well as expanded immune gene families is not unique to Atlantic cod - but most likely a feature common to all codfishes. A shared expansion of NLR genes in teleosts suggests that the NLRs have a more substantial role in the innate immunity of teleosts than other vertebrates. Moreover, we find that high copy number genes combined with variable genome assembly qualities may impede complete characterization, i.e. the number of NLRs might be underestimates in the different teleost species.

genomics↗