| Summary: | 碩士 === 國立臺灣大學 === 畜產學研究所 === 92 === Tsaiya duck is the major egg-laying duck in Taiwan that has high egg production rate. To support egg yolk lipid deposition for Tyaiya duck needs a high lipid generation machinery to support the egg yolk lipid accumulation. In mammals, sterol regulatory element binding protein 1 (SREBP1) drives the expression of several lipogenic genes whereas SREBP2 dictates the expression of every gene involved in cholesterogenesis. The expression of these two genes and their target genes is an indication of the capability of hepatic lipid metabolism. The ability of adequate lipid formation is an assurance for yolk lipid deposition. With much of the emphasis been on mammalian species, the expression of SREBP1 and SREBP2 and their relation with avian lipid metabolism has not been well characterized. Very low density apolipoprotein-II (apoVLDL-II), a protein only expressed in female birds, plays an important role on lipid transportation from liver to ovary, and has not been studied for Tsaiya duck. Our purposes are to clone the gene fragments of Tsaiya duck SREBP1, SREBP2, FAS, HMG CoA reductase, and apoVLDL-II, the genes associated with lipid metabolism and to determine tissue distribution of these genes. The effects of egg-laying on the mRNA concentrations of SREBP1, SREBP2, FAS, HMG CoA reductase, and ApoVLDL-II in liver of Tsaiya ducks were also studied.
Fifteen ducks right before the first egg was laid (18-wk old) and 15 ducks from the same population at a egg production rate of 80 % were sacrificed. Adipose tissue, cardiac muscle, skeletal muscle, liver, and ovary were quickly dissected, frozen in liquid nitrogen, and stored at –80 ℃. The total RNA was extracted and used to clone the genes fragments of SREBP1, SREBP2, FAS and HMG-CoA reductase by RT-PCR. We also cloned the Tsaiya duck apoVLDL-II full length cDNA from a Taiya duck liver cDNA library。The data showed that Tsaiya duck SREBP1, SREBP2, FAS and HMG-CoA reductase were highly homologous to that of chicken, indicating the genetic relationship between those two species was close. The tissue distribution of this five genes were determined by northern analysis. The data showed that Tsaiya duck SREBP1 mRNA was expressed in adipose tissue, cardiac muscle, skeletal muscle, liver, and ovary. The SREBP2 mRNA concentration was high in the liver and ovary. The FAS and HMG-CoA reductase mRNA were highly expressed in the liver and to a lesser extend in other tissues. The apoVLDL-II mRNA was specificly expressed in the liver. The differences of mRNA concentrations of SREBP1, SREBP2, FAS in the livers of laying and pre-lay ducks were not significant. However, the concentrations of hepatic HMG-CoA redutase and ApoVLDL-II mRNA were higher in the laying ducks than that of pre-lay duck. The data suggest that laying may affect particular aspect of lipid metabolism, especially biochemical pathways that apoVLDL-II and HMG-CoA reductase were involved. The data of suppression subtractive hybridization showed that the expression of genes such as vittellogenin and apoVLDL-II, genes asociated with yolk formation and lipid metabolism, was increased after laying. The expressed differentiation of the genes we cloned were needed more confirmation. We also cloned many novel genes and their function attend at egg-laying were needed confirmation. The differentially expressed genes need further confirmation. The functions of those novel genes discovered in the suppression subtractive hybridization need to be studied.
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