分析人類肝臟的表現基因

Abstract

肝臟於人體生理學上扮演一相當重要的角色﹐因為肝臟同時須負責 分解代謝､合成以及解毒等多種生命維持的必備功能﹐也因如此﹐其基因 表現的複雜度由此可想見。 我們嘗試以新的分析法-複雜精簡化分析法﹐ 配合生物資訊的應用﹐藉由比較胎兒與成人肝臟細胞的表現基因﹐找出發 育性調節基因﹐藉著這些基因的研究﹐探索其在發育過程中所扮演的角色 ﹔並試著找出這些基因與肝癌形成的相關性﹐希望能以不同的角度與出發 點找出疾病衍發的根源。我們總共挑選220個表現於胎兒肝臟的基因片段 進行分析﹐最後 得到188個不同的基因片段﹐其中有167個片 段與資料庫中序列有90%以上的相似性﹐另有21個片段則與資料庫中已存 在基因序列的相似性偏低。經由實驗確認這21個基因片段﹐除了有4個無 法確認表現外，其餘17個基因片段經確認後發現一些很有趣的現象。在這 些基因片段中﹐有些如預期中的只表現在胎兒肝臟的表現量遠遠大於成人 ﹐而且同時表現在肝癌細胞株中﹐可能不失為一發育或癌症發生的指標﹔ 也有一些基因片段的表現情況﹐可能是胎兒肝臟的表現量低於成人肝臟或 兩者表現量相當﹐但基因的表現具有器官專一性或是在肝 癌細胞株中的 表現量較正常肝臟有升高、降低的變化﹔另有一些基因在人類尚未被發現 ﹐但在其他種類生物已被發覺﹐而且也已知道功能﹔此外﹐我們亦藉由資 料庫的連結､查詢﹐將資料庫中已存在的基因片段藉由我們所找到的片段 而連結成一條比原先更長的基因序列﹐並都已經過實驗確認無誤。 Liver is a vital organ in humans and play many essential physiological rolesin metabolism and detoxification. The gene expression pattern of the liver is expected to be complex. In this study, we employed two new techniques, namely the complexityreductionanalysis and bioinformatics, to investigate genes expressed in thefetal and adult livers. The expression of genes that are developmentallyregulated were also examined in established human hepatoma cell lines. Fromthe profiles of fingerprinted expressed genes, a total of 220 fetal liver cDNAfragments were isolated, cloned, and sequenced. Extensive database search of188 unique sequences revealed that 167 fragments had matches greater than 90%in the databases. The remaining 21 expressed sequences of no matches found in the Human Genome Index (HGI) were potentially novel. All but 4 were confirmedas human genes by the reveres transcription-polymerase chain reaction(RT-PCR)using cDNA templates prepared from the normal fetal and adult livers and thehepatoma cell lines and by the Northern blot analysis. Of the 17 potential human genes, 6 were expressed predominantly in the fetal liver and a half of which showed an elevated level of expression in Hep-G2 cells. Four genes were expressed at a higher level in the adult tissue and their expression appeared to be down-regulated in the hepatoma cell lines. The expression of the remaining 7 genes was not modulated. Expression of these genes in human fetal and adult tissues was also examined by the Northern blot analysis. Both the tissues-restricted expression patterns and multiple transcripts of the same gene were observed. In addition, electronic cloning was performed on the computer by assembling the expressed sequence and its overlaping fragments in the databases into a contig.