鯉魚 c一myc基因之結構分析與表現研究

Abstract

中文摘要 c－myc 為一種 proto-oncogene ，在細胞之生長與分化過程扮演了重要角色，目前已在多種動物細胞中發現。本論文自鯉魚腦下腺cDNA 基因庫與紅血球Genomic基因庫中均篩選出 c一myc 基因。經核酸序列分析結果得知本實驗所篩選之 c－myc cDNA 長度為 990bp ，其解譯區包含了 c－myc ）C 端 218 個胺基酸之遺傳密碼，因此，此 cDNA 並非 c－myc 基因全長之 cDNA 。而自紅血球基因庫所獲得之 c－myc 基因已完成了 2563bp 之核酸序列，其中包含了 c - myc 完整的解譯區，即 0 . 7kb 和 1 . 3kb 長之 Exon2和 3 ，以及 266bp 長之 intron2 。由解譯區推導出來的鯉魚 c－myc 包含 390 個胺基酸，其初級結構與其他脊椎動物極為相似。由於這兩個基因之核酸序列不盡相同（相似性 90 % ) ，因此推測鯉魚可能有一種以上的 c－myc 基因。 由 RNA dot hybridization 分析之結果發現， c－myc 基因在鯉魚腦、肝、腎臟及腦下腺等組織之表現相當低，而在發育早期之卵巢則有較明顯之表現。此外，由 Primer extention 的結果顯示鯉魚腦下腺 c－myc 基因可能有三個轉錄起始點（ transcriptional initiation site ) ，而且腦下腺與卵巢所表現之 c - myc 基因可能不同。對於 c－myc 基因表現之調控機制以及組織特異性則有待進一步探討。

ABSTRACT c-myc, one kind of proto-oncogene, has been found in many species of animals. It plays an important role in cellular growth and differentiation. In this paper, encoding c-myc cDNA and c-myc genome have been isolated from carp pituitary cDNA libraries and a carp erythrocyte genomic library, respectively. The cDNA obtained is 990 bp long which encodes the C- terminal 218 amino acid residues of c-myc. suggesting that this cDNA is lacking the 5’ end of c-myc. The 2563 bp of c-myc genome isolated has been sequenced. It contains the entire coding region, 0.7kb of exon2, 1.3kb of exon3, and a 266 bp intron2. The 390 amino acid-residue sequence deduced from the coding region shows great similarity to c-myc of other vertebrates. Since the two nucleotide sequences of carp c-myc are not the same (nucleotide homology is 90%), there may be more than one c-myc gene in carp. RNA dot hybridization analysis indicates that the RNA level of c－myc is low in carp brain, liver, head kidney and pituitary gland, but is high in ovary of early developmental stage. By primer extention experiment, three transcriptional initiation sites may be present in carp pituitary c-myc gene. It becomes interesting to study the regulation and the tissue specific expression of c-myc in carp in the future.