Tissue distribution of transcription for 29 lipid metabolism-related genes in turbot (Scophthalmus maximus)

The distribution patterns of adipose tissue in different fish species are highly diverse. Turbot (Scophthalmus maximus) has a special lipid storage pattern, storing lipid predominantly in the subcutaneous tissue around the fin. In order to better understand the lipid physiology of fish storing lipid in subcutaneous tissue, this study preliminarily investigated the tissue distribution of 29 lipid metabolism-related genes in S. maximus, which are involved in lipogenesis, fatty acid oxidation, biosynthesis and hydrolysis of glycerides, lipid transport, and relevant transcription regulation. Fifteen tissue samples including eye, gill, brain, skin, muscle, liver, stomach, kidney, spleen, heart, foregut, pyloric caeca, hindgut, caecum and subcutaneous adipose tissue around the fin were collected from 30 fish for qRT-PCR analysis (10 fish as a replicate pool). In the PCR experiment, EF1α and RPL13 were used as the reference genes. The amplification efficiency for all primers, which was estimated by standard curves based on dilution series of target template, was within 95%-105%, and the coefficients of linear regression (R²) were ˃0.99. A quantitative thermal cycler (Roche LightCycler 96, Basel, Switzerland) was used for the real-time qPCR, and the reaction system and program followed the formal procedures in our laboratory. Each sample was run in triplicate. The mRNA levels were expressed according to the 2^−ΔΔCT method. For each gene, the mRNA level in the tissue with the lowest expression was standardized to be 1.0, and the gene expression levels of other tissues were expressed as folds of 1.0. The results showed that the intestine and brain had high transcription of lipogenic genes such as ACACβ, FAS and SCD1, whereas the liver and muscle had low expression levels of these genes. The intestine also had the highest transcription levels of most apolipoproteins such as ApoA1, ApoA4, ApoB100, and ApoEα and lipid metabolism-related transcription factors such as PPARα1, PPARγ, SREBP1, LXR-α, and HNF4α. The transcription of fatty acid β oxidation-related genes, ACOX1, ACOX3, and CPT1, was low in the muscle. The intracellular glyceridases, HSL, DAGLα, and MGLL, were highly transcribed in the brain, eye, and heart. In conclusion, in S. maximus, the intestine may not only be the place for lipid uptake, but also an important lipogenic organ in S. maximus. The lipid metabolism in the subcutaneous adipose tissue of S. maximus is not active, which may be due to the fact that the subcutaneous tissue is the main organ for lipid storage in S. maximus. This study will help to further elucidate the regulation of lipid metabolism in fish at the molecular level.