Øivind Andersen

Background/objectives: Tropoelastin is a highly hydrophobic extracellular matrix protein responsible for the extensibility and elastic recoil of various organs. The Windkessel effect in blood vessels dampens pressure variations during the cardiac cycle to provide continuous perfusion of tissues, such as the fragile gill capillaries in fish. The teleost-specific whole-genome duplication was followed by structural and functional divergence of the duplicated tropoelastins, of which ElnB confers the uniquely low stiffness of the bulbus arteriosus. Methods: We have examined the diversity of tropoelastins in all major fish clades by searching for tropoelastin (eln) genes in the sequenced genomes. Duplication of eln genes in tetraploid salmonids and cyprinids was examined by maximum likelihood phylogenetic analysis, and cardiac eln expression in rainbow trout was quantified by qPCR. Results: The tetraploid salmonid genomes harbor two elna genes but a single elnb, except for the tandem duplicated elnb genes in sockeye salmon and lake whitefish, while the tetraploid common carp possesses four elna and elnb genes on separate chromosomes. Rainbow trout showed strong elastin staining in the larval bulbus and ventral aorta, and the bulbar expression of elnb was 15 times higher than the ventricular levels in juvenile fish. The expression of elna1 and elna2 was also significantly higher in the bulbus, and together their transcript levels were almost similar as the elnb levels. The overall hydrophobicity of the fish tropoelastins differed considerably among the species ranging from 28.6% in Emerald rockcod ElnB to 56.3% in lesser devil ray Eln, but showed no significant difference with the tetrapods examined, except for the lower hydrophobicity of teleost ElnB. Conclusions: The inclusion of tetrapods in the analysis revealed a positive relationship between ventral aortic blood pressure and tropoelastin hydrophobicity.

Background/objectives: Elastin is a highly hydrophobic extracellular matrix protein responsible for the extensibility and elastic recoil of various organs. The Windkessel effect in blood vessels dampens pressure variations during the cardiac cycle to provide continuous perfusion of tissues. Duplication of the elastin gene in teleost fish led to the neofunctionalization of the ElnB paralog, which confers the uniquely low stiffness of the bulbus arteriosus to protect the fragile gill capillaries from large pressure variations. Methods: We have examined the diversity of elastins in all major fish clades by searching for eln genes in the sequenced genomes. Results: Tetraploid salmonids have two elna genes but a single elnb, except for the tandem duplicated elnb genes in sockeye salmon and lake whitefish, while the tetraploid common carp possesses four elna and elnb genes on separate chromosomes. Rainbow trout showed strong elastin staining in the larval bulbus and ventral aorta, and elnb was highly expressed in the bulbus of juvenile and adult fish. Teleost ElnB differs from the ElnA paralog by containing considerably longer hydrophobic domains. The single elastin in cartilaginous and lobe-finned fish showed high overall hydrophobicity, and no relationship was found between the hydrophobicity levels of fish elastin and the ventral aortic blood pressure. Conclusion: The differential gene expression of teleost elna and elnb during cardiac development probably evolved together with the divergence in the genetic structure that resulted in larger hydrophobic domains of the ElnB paralog and decreases stiffness of bulbus arteriosus.

Background/Objectives: Inactivation of the dnd gene involved in the development of primordial germ cells (PGCs) leads to the loss of gametes and halts reproductive development. Studies on sterile fish allow for the identification of genes and processes associated with GC differentiation. Methods: Atlantic salmon with GC-ablated testes were produced by temporal silencing of dnd. Gene expression was analyzed in sterile and fertile testes using 44k microarray and qPCR. Results: In sterile testes, transcripts of several GC markers were detected at low levels, suggesting the presence of cells with a GC-related expression profile that failed to initiate spermatogenesis. Expression of 260 genes was undetectable in the gonads of sterile males and females, and 61.5% of these were also inactivated during first maturation of fertile testes. This group was enriched with genes highly expressed in the brain, including those involved in endocrine and paracrine regulation, synaptic transmission, and numerous genes critical for brain development; among them, 45 genes encoding homeobox proteins. Another group of 229 genes showed increased expression in developing testes and included genes involved in neurosecretion and brain development regulation. GC-ablated testes showed increased expression of reproductive regulators such as amh and sdy and numerous immune genes, suggesting a reprogramming of GC-depleted testes. Temporal silencing of dnd indicated common developmental processes in the brains and gonads of Atlantic salmon testis that become inactive in testes at first maturation. These processes may play roles in PGC homing, the creation of a specific environment required for spermatogenesis, or facilitating communication between the gonads.

Inactivation of the dnd gene, which is essential for the development of primordial germ cells (PGCs), leads to the loss of gametes and halts further reproductive development in vertebrates. Studies on the gonads of sterile fish are useful for identifying GC-related genes, as well as the structures and processes dependent on this lineage. We identified genes affected in GC-ablated testes of Atlantic salmon following temporal silencing of dnd and tracked their expression during normal gonadal development. In sterile testes, transcripts of several GC markers were detected at low levels, suggesting the presence of cells with a GC-related expression profile that failed to initiate spermatogenesis. We found 260 genes silenced in the gonads of sterile males and females, and 61.5% of these were also inactivated during first maturation of fertile testes. This group was enriched with genes highly expressed in the brain, including those involved in endocrine and paracrine regulation, synaptic transmission, and numerous genes critical for brain development, among them, 45 genes encoding homeobox proteins. Another group of 229 genes showed increased expression in developing testes and included genes involved in neurosecretion and brain development regulation. Genes upregulated in GC-ablated testes included reproductive regulators such as amh and sdy, as well as numerous genes related to the innate and adaptive immune systems, suggesting a reprogramming of germ cell-depleted testes. Temporal silencing of dnd revealed the presence of a complex neural structure in the Atlantic salmon testis that becomes inactive at first maturation. Potential roles for this structure may include PGC homing, the creation of a specific environment required for spermatogenesis, or facilitating communication between the gonads and brain to signal readiness for reproduction, among other possibilities.

Light and photoperiod vary in a predictable manner throughout the daily and annual cycle that is utilized by organisms to direct processes of living. The aquaculture industry applies light to manipulate salmon development, but the effects have not yet been thoroughly investigated in early ontogeny. Here, salmon eggs and larvae were subjected to three different light regimes (continuous dark, continuous light and compressed simulated natural photoperiod [LD] to provide calendar time information). The expression of eight clock- and melatonin-related genes (clock1a.2, arntl1a.2, per1b, per2a, cry3b, nr1d1a, aanat2b, mtnr1b) was examined through one daily cycle before eyeing, after eyeing, and before start-feeding. Clock1a.2 and per2a showed indications of being maternally deposited, and expression increased for most genes through development. All genes showed clear differences in expression between light regimes, and rhythmically expressed genes were more abundant and with stronger rhythms under LD regime. Aanat2b was rhythmically expressed before eyeing, and all genes were rhythmically expressed under LD at start-feeding. Interestingly, at this time, the positive, negative, and stabilizing arm of the clock peaked simultaneously along with the melatonin-related genes mid-photophase. These results implore greater attention to the lighting conditions used during early development, as different lightings could have lasting effects.

Ectothermic marine animals vary widely in their tolerance to temperature changes, and polar stenothermal species seem to have poor ability to compensate for a rise in water temperature. The sub-Arctic snow crab (Chionoecetes opilio Fabricius, 1788) lives in the northwestern Atlantic Ocean and northern Pacific Ocean at temperatures ranging from about −1.5 °C to 4 °C. Since the metabolic costs overtake caloric intake above 7 °C, the snow crab appears to be energetically restricted to cold water. We investigated thermal stress responses in adult male crabs exposed to a sudden temperature increase to 9.5 °C for 24 hr after four weeks of acclimation at 2.5 °C or 5.5 °C. Heart-rate loggers implanted in a limited number of crabs showed 60% increase in cardiac activity during the thermal stress. Surplus oxygen supply in all crabs was inferred by the low hemolymph lactate and unchanged glucose levels, but only the crabs acclimated at 5.5 °C were still active at the elevated temperature. Low heat shock and oxidative stress responses were suggested by the missing upregulation of the genes encoding four heat shock proteins (Hsp70a, Hsc71, Hsp90a2, Hsp60) and the antioxidative enzymes superoxide dismutase and catalase. The trend towards inverse temperature-dependent on the expression of the hsp genes may be related to increased protein damage at low temperatures, or possible trade-offs between costs and benefits of producing heat shock proteins at elevated temperature. Although adult snow crabs seem to be able to cope with short-term heat stress, the tolerance to chronic elevated temperatures should be further examined using a larger number of individuals.

Non-synonymous variation (NSV) of protein coding genes represents raw material for selection to improve adaptation to the diverse environmental scenarios in wild and livestock populations. Many aquatic species face variations in temperature, salinity and biological factors throughout their distribution range that is reflected by the presence of allelic clines or local adaptation. The turbot (Scophthalmus maximus) is a flatfish of great commercial value with a flourishing aquaculture which has promoted the development of genomic resources. In this study, we developed the first atlas of NSVs in the turbot genome by resequencing 10 individuals from Northeast Atlantic Ocean. More than 50,000 NSVs where detected in the ~ 21,500 coding genes of the turbot genome, and we selected 18 NSVs to be genotyped using a single Mass ARRAY multiplex on 13 wild populations and three turbot farms. We detected signals of divergent selection on several genes related to growth, circadian rhythms, osmoregulation and oxygen binding in the different scenarios evaluated. Furthermore, we explored the impact of NSVs identified on the 3D structure and functional relationship of the correspondent proteins. In summary, our study provides a strategy to identify NSVs in species with consistently annotated and assembled genomes to ascertain their role in adaptation.

The germ cells are essential for sexual reproduction by giving rise to the gametes, but the importance of germ cells for gonadal somatic functions varies among vertebrates. The RNA‐binding dead end (Dnd) protein is necessary for the specification and migration of primordial germ cells to the future reproductive organs. Here, we ablated the gametes in Atlantic salmon males and females by microinjecting dnd antisense gapmer oligonucleotides at the zygotic stage. Precocious maturation was induced in above 50% of both germ cell‐depleted and intact fertile males, but not in females, by exposure to an off‐season photoperiod regime. Sterile and fertile males showed similar body growth, but maturing fish tended to be heavier than their immature counterparts. Pituitary fshβ messenger RNA levels strongly increased in maturing sterile and fertile males concomitant with the upregulated expression of Sertoli and Leydig cell markers. Plasma concentrations of 11‐ketotestosterone and testosterone in maturing sterile males were significantly higher than the basal levels in immature fish, but lower than those in maturing fertile males. The study demonstrates that germ cells are not a prerequisite for the activation of the brain–pituitary–gonad axis and sex steroidogenesis in Atlantic salmon males, but may be important for the maintenance of gonadal somatic functions.

Turbot is an important flatfish widely distributed along the European coasts, whose fishery is centered in the North Sea. The commercial value of the species has boosted a successful aquaculture sector in Europe and China. Body growth is the main target of turbot breeding programs and is also a key trait related to local adaptation to temperature and salinity. Differences in growth rate and optimal growth temperature in turbot have been shown to be associated with a hemoglobin polymorphism reported more than 50 years ago. Here, we identified a Gly16Asp amino acid substitution in the β1 globin subunit by searching for genetic variation in the five functional globin genes within the whole annotated turbot genome. We predicted increased stability of the turbot hemoglobin by the replacement of the conserved Gly with the negative charged Asp residue that is consistent with the higher rate of αβ dimer assembly in the human J-Baltimore Gly16β->Asp mutant than in normal HbA. The turbot Hbβ1-Gly16 variant dominated in the northern populations examined, particularly in the Baltic Sea, while the Asp allele showed elevated frequencies in southern populations and was the prevalent variant in the Adriatic Sea. Body weight did not associate with the Hbβ1 genotypes at farming conditions (i.e., high oxygen levels, feeding ad libitum) after analyzing 90 fish with high growth dispersal from nine turbot families. Nevertheless, all data at hand suggest that the turbot hemoglobin polymorphism has an adaptive significance in the variable wild conditions regarding temperature and oxygen availability.