老鼠肝再生基因表現之研究

Abstract

摘要 老鼠肝再生向來是研究生長調節與控制的一個很好的實驗模式。老鼠肝經部分切除後，在一段時間內會由細胞之分裂或分化長回原來大小。這種受到調節與控制的生長，在分子層次上之基因表現必然發生了不尋常的改變，使原本已分化成熟的肝細胞重獲細胞分裂的能力。為了找出肝再生過程中特有的基因表現，在本文中從建立一個肝再生時的互補基因庫開始，經差異篩選，找出八個在再生過程中有差異表現的互補基因(cDNA)。利用Northern blot的分析，發現各個互補基因在肝再生不同時間時的表現各有差異。這種差異主要為量方面的改變，而非無與有的差別。此點與前人研究結果相符。又從部分核酸序列分析，得知其中兩個互補基因分別為α1-acid glycoprotein (AGP)及fibrinogenβchain。 由完整的核酸序列分析及由核酸序列推出的胺基酸序列之比較可知，小老鼠(mouse)的AGP與大老鼠(rat)的相對蛋白質有71％的同源性(homology)，而與人類有40％的同源性。同時，在此三個(小老鼠、大老鼠、人類)AGP中，接上醣類分子串及重脬胺基酸(Cystine)的位置也幾乎完全相同，這種位置的保留性(conservation)表示醣類分子串及二硫化鍵(disulfide bond)的形成極可能在AGP的功能上扮演著重要的角色。另一方面，由目前所得到的fibrinogenβchain核酸序列及胺基酸序列發現，小老鼠及人類的相對蛋白質有相當高的同源性(86%)，顯示這種蛋白質在演化過程中相當穩定(conserved)。

Summary The mammalian liver regeneration has been an excellent system for study of growth regulation. In order to find regeneration-related genes, or genes that involve in growth regulation, a cDNA library was constructed using liver poly (A) +RNA from Balb/c mouse (male) 26 h after partial hepatectomy. Eight clones were isolated by differential screening of the cDNA library using probes prepared from quiescent and 26 h post-hepatectomized poly (A) +RNAs. Northern blot analysis was performed to study the expression pattern of the individual clone during the course of regeneration. The results showed that the level of expression varied at different time of liver regeneration. All the changes were quantitative, rather than qualitative, which is in good agreement with the results obtained by other groups. All of the eight cDNA clones were partially sequenced. By searching the NIH data bank, two of the eight clones, mLR 15-2 and mLR 19-5, were identified to be αl-acid glycoprotein and fibrinogenβchain respectively. They share extensive amino acid sequence homology with the corresponding rat or human sequences. Near full-length cDNA of al-acid glycoprotein (AGP) and fibrinogen β chain were sequenced and their amino acid sequences deduced. Complete AGP coding region was obtained. Mouse AGP amino acid sequence has 71% homology with rat AGP and 40% homology with human AGP. N-linked glycosylation sites and cysteine residues that involve in disulfide bond are highly conserved among the three proteins, which suggest they may be related to the biological function of AGP. On the other hand, mouse fibrinogenβchain amino acid sequence obtained so far shows 86% homology with human fibrinogenβchain. The results suggest that the fibrinogenβchain is highly conserved in evolution.