| Temperature is an important factor to maintain life activities,almost affects all physiological and biochemical processes of fish,and then affects all life activities of fish.Different fish have their most suitable growth temperature range.When the ambient temperature is too low,it will have adverse effects on fish,such as decreased appetite,slow growth,abnormal metabolism,decline in immunity and so on.When the ambient temperature continues to decrease or the duration of cold stress continues to increase,it will cause fish tissue damage and even lead to fish death.At present,many farmed fish species have the characteristics of not tolerating low temperature,and the artificial breeding has strict temperature requirements.Therefore,it is important to study the response of fish to cold shock and its mechanism of action.Stearoyl-coenzyme A desaturase(SCD),also known as Δ9 Fatty acid desaturase(Δ9 FAD),is a member of fatty acid desaturase(FAD)family.SCD is a transmembrane protein located on the endoplasmic reticulum and is the rate-limiting enzyme that catalyzes the synthesis of monounsaturated fatty acids from saturated fatty acids.The saturated fatty acid substrates it acts on are stearoyl-Co A(C16: 0)and palmitoyl-Co A(C18: 0),introducing hydrogen bonds between the ninth carbon atom and the tenth carbon atom respectively,and two monounsaturated fatty acids are formed,oleic acid(C16: 1)and palmitic acid(C18: 1).These two unsaturated fatty acids are substrates for the synthesis of triglycerides,cholesterol esters,wax lipids and membrane phospholipids.Membrane phospholipids are an important component of cell membranes,so SCD controls the content of unsaturated fatty acids in cell membranes,which is of great significance to the fluidity of cell membranes.Studies have found that the expression level of scd gene in carp,tilapia,large yellow croaker,etc.is significantly increased under cold shock,suggesting that scd gene plays an important role in fish cold stress,but the specific function and molecular mechanism are not sure.In this study,we selected the model animal zebrafish as the research object.First,real-time PCR method was used to detect the expression pattern of scd gene in zebrafish embryos and zebrafish tissues,and it was found that the scd gene was maternally expressed in zebrafish embryos and showed zygotic gene expression after a certain period of development,scd is expressed in various zebrafish tissues,with the highest expression levels in the brain and liver.Then the zebrafish embryos were subjected to cold stress at different times,and it was detected that the zebrafish scd gene and related genes were significantly up-regulated under cold shock.Then the amino acid sequence of the zebrafish SCD protein was compared and analyzed,and it was found that the structure and function of the SCD protein during species evolution were highly conserved.Finally,the over-expression vector of scd gene was constructed in vitro and successfully expressed in cells.In summary,this subject further verified that the expression level of scd gene in zebrafish was significantly up-regulated after cold stress,proving that the scd gene is involved in the cold stress of zebrafish.Combined with the related research of SCD protein in cell function,we speculate that this phenomenon may be related to the fluidity of the cell membrane at low temperature.This hypothesis provides a new idea for the study of the cold stress mechanism of zebrafish.In addition,the construction of scd gene overexpression vectors has accumulated material for further research on the function of the zebrafish scd gene,and laid the foundation for the cultivation of zebrafish that overexpress the scd gene. |
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