There are 10 percent to 15 percent genes expression in certain cells during the life time of fishes like other vertebrates. The genes were different at different development stage, under different physiological conditions, and in different kinds of cells. So comparing the differences of gene expression in different cells can help us understand the genetic nature of phenotypic differences, and understand the basic information of life period, and find the genes in relation to development and diseases, and finally benefit mankind. Several methods were developed to clone differential expression gene in recent years. They are subtractive hybridization (SH), differential display (DD),representional difference analysis (RDA), and so on. These methods all have postive influences on cloning special genes, but they all have some defects, such as higher false-positive, lower replication, lower sensitive and difficulty to manipulate. Suppression subtractive hybridization (SSH) was developed by Diatchenko et al in 1996. SSH was based on suppression PCR and combines normalization and subtraction in a single procedure. It is a more effective and convenient method than all others mentioned above. The principle and the rules of manipulation of SSH in detail was illuminated and the novel genes cloned by SSH was listed. They are immune related genes and reproduction and development related genes. The reproduction and development related genes are as follows: ZP3, Cyclin A2,CBI02, YA2, FSTRAP. The immune related genes are as follows: NKEF(natural killer enhancing factor), CC chemokine, CXCR1, CXCR2, CXCR4, AIF-1(allograft inflammatory factor-1), IL-1β(inteleukin-1), FcεRIγ(γ submit of high affinity Fc receptor for IgE), SSA(serum amyloid A), LECT2 (leucocyte cell-derived hemotaxin 2), GMFβ(glia maturation factorβ), CD45, Lysozyme C, PBEF (Pre-B cell enhancing factor), C-type lectin,PTX(Pentraxin), IL-1RⅡ, IL-8-1ike CXC chemokine, TF(tissue factor), trout chemokine 2, TNF decoy receptor,M17. Some subtracted cDNA libraries were also built by SSH method.
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