Why the lipid deposition in the muscle fibers and myosepta is selective in triploid rainbow trout? A lncRNA‒mRNA study

Salmonids can accumulate lipids in their fillets, creating marbled features with alternate red (Muscle Fibers, MF) and white stripes (Myosepta, MS). To investigate the regulation of this important quality trait, diets with low and high lipid levels were fed to the fish and found that high lipid diet significantly elevated muscular lipid deposition in MS but not in MF. Then, a whole-transcriptome analysis was performed and results showed that the mRNA expression of ACSL1 and GADD45A was downregulated by the lncRNAs MSTRG.19477.1 and XR_005039693.1, resulting in consistent lipid contents in the MF from both groups. The lncRNAs MSTRG.21618.1, XR_005034756.1, XR_002473790.2, XR_002472790.2, and MSTRG43906.1 increased lipid deposition in MS30 by upregulating the mRNA expression of ELOVL2, DGAT2, LCAT, etc. In conclusion, the present study revealed that selective muscular lipid deposition and several lncRNAs may play key roles in regulating the marbling features of rainbow trout.