Browsing by Subject "Atlantic salmon"

Three-dimensional (3D) cellular cultures have been shown to represent tissue formations and functions more accurately than two-dimensional (2D) cultures and have been successfully utilized more accurately in model organisms, e.g., to understand cellular modular functions. However, the applications in non-model organisms are limited, and to our knowledge have not been implemented in ectotherms. At an ecological scale, the technique can enhance our understanding by providing insights on cellular and tissue level molecular mechanisms. A potential implementation of this method in Atlantic salmon is to elucidate the molecular function of the vestigial-like 3 (vgll3) gene, which plays a central role in salmonid maturity, potentially by regulating energy allocation via regulating adipogenesis. In this thesis, a proof of principle study was implemented, where the feasibility of obtaining and maintaining a suspension 3D adipose tissue culture in Atlantic salmon (Salmo salar) was assessed. The harvested visceral white adipose tissue from around the intestinal tissue of mature Atlantic salmon (salmon past smolt stage) was first separated into stromal vascular fraction (SVFs) and mature adipose fraction (MAFs). SVFs contain preadipocytes (precursors of adipocyte cells) in addition to a variety of other cell types. MAFs are mature adipocytes. Both MAFs and SVFs were successfully maintained in-vitro for over four weeks. SVFs were then successfully differentiated into mature adipocytes, demonstrating the feasibility of studying adipogenesis in Atlantic salmon. Proof of this methodology and its further implications may help us to understand the cellular functions of vgll3 and may subsequently help to better understand its causal relation to the maturation process in Atlantic salmon.

Atlantic salmon (Salmo salar) have a complex life history, characterized by a juvenile stage spent in freshwater before migrating to the sea for one to several years and then returning to their natal river to spawn. Sea-age at maturity, which corresponds to the number of years spent at sea, is an important life-history trait influenced by environmental and genetic factors. Variation in sea-age at maturity in Atlantic salmon has been associated with a SNP located in the intron of six6 on chromosome 9 (six6a). This gene is also known to be evolutionary conserved in eye development in vertebrates and has a crucial role in sexual maturation in mammals. In 3-year-old Atlantic salmon, six6a was found to be expressed in the eyes, brain, gills, and testes. In addition, in situ hybridization has shown that six6a is expressed in multiple organ systems in embryos, for example, the eye and brain developing areas. However, quantification of its level of expression has only been carried out on whole individuals so far. Therefore, this thesis aims to quantify the expression level of six6a, and its paralogue, six6b, at different time points (1-9 months post-hatching) and in four different tissues and a body part (brain, eye, gill, hypothalamus, and head) to identify the tissues and developmental stages that are relevant for future functional studies on the association between six6a genotype and variation in sea-age at maturity. Using a 3’ RNA sequencing approach we found that the eyes and hypothalamus had the highest expression level of both paralogues with a higher expression level of six6b. The expression of the two paralogues in gill samples was very low or non-existent and the low level of expression detected in head and whole brain samples could be influenced by the presence of the eyes and the hypothalamus, respectively. Based on these results, the hypothalamus and eyes would be important tissues for further investigation to gain more information on the association between the six6a genotype and variation in sea-age at maturity in Atlantic salmon. In addition, a more in-depth analysis of the transcriptomic data obtained would allow the investigation of the specific roles of each paralogue, for example by studying correlated genes in the different tissues.

In teleost fish, various egg traits play a crucial role in the development, growth, and survival of the offspring and thus affect maternal reproductive success. Atlantic salmon (Salmo salar) is a species where age at maturity, an important life-history trait influencing reproductive success, is under environmental and genetic control. In this study, I assessed how genetics of the vgll3 genotype and the dietary energy content affect egg traits and female maturation rate. The fish used in this study were lab-bred, three-year- old female Atlantic salmon with different vgll3 genotypes fed on one of two diets differing in energy content. The eggs traits included in the study were egg size, lipid, and protein content. Female maturation rate was not affected by the energy level of the diet or the vgll3 genotype. Egg size expressed as egg dry weight differed between females in the two feed treatments. These differences may be attributed to the increased lipid content of the eggs due to the higher fat content of the maternal diet. Females receiving high energy feed had a significantly higher egg lipid content compared to the low energy feed treatment. Females homozygous for the vgll3 allele associated with early maturity had a significantly lower egg lipid content in comparison to the females homozygous for the vgll3 late maturity allele indicating a potential reproductive fitness cost associated with early maturity. No effect of diet or vgll3 was found in egg protein content. This study provides the first evidence of vgll3 not only affecting Atlantic salmon age at maturity, as found in previous studies, but also egg lipids through maternal provisioning of nutrients.