Niimi T, Yamashita O, Yaginuma T
Laboratory of Sericulture and Entomoresources, School of Agricultural Sciences, Nagoya University, Japan.
Insect Mol Biol. 1996 Nov;5(4):269-80. doi: 10.1111/j.1365-2583.1996.tb00101.x.
In an initial effort to understand the molecular mechanism of how low temperature induces sorbitol dehydrogenase gene expression in diapause eggs of the silkworm, the sorbitol dehydrogenase gene was isolated from a Bombyx genomic library using a cDNA encoding the Bombyx homologue of mammalian sorbitol dehydrogenase as a probe. The gene extended for about 10 kb, consisting of eight exons and seven introns. Four TATA motifs were found in the 5' upstream region of the gene, without CCAAT. AATTAA, instead of AATAAA, was localized in the upstream region of the polyadenylation site. Although a single copy of this gene was present per haploid genome, 1.2 kb and 1.1 kb transcripts were found from yolk cells in diapause eggs and from larval fat-body cells, respectively. The two major transcription initiation sites corresponding to both transcripts were localized at 355 and 226 base pairs upstream from the transition start site, indicating an alternative use of promoter. The 5'-upstream region of the gene contained a consensus sequence, TGA(A/T)AA(A/G/T), that has been found in insect genes expressed mainly in larval and pupal fat bodies. It also contained three kinds of sequences similar to cis-elements recognized by members of the steroid receptor superfamily, such as chicken ovalbumin upstream promoter transcription factor (COUP-TF)/Drosophila Seven up (SVP), Drosophila hormone receptor 39 (DHR39) and Bombyx fushi tarazu transcriptional factor 1 (BmFTZ-F1).
为初步了解低温诱导家蚕滞育卵中山梨醇脱氢酶基因表达的分子机制，以编码哺乳动物山梨醇脱氢酶家蚕同源物的cDNA为探针，从家蚕基因组文库中分离出山梨醇脱氢酶基因。该基因长度约为10 kb，由8个外显子和7个内含子组成。在基因的5'上游区域发现了4个TATA基序，没有CCAAT。位于多聚腺苷酸化位点上游区域的是AATTAA，而不是AATAAA。尽管单倍体基因组中该基因只有一个拷贝，但分别从滞育卵的卵黄细胞和幼虫脂肪体细胞中发现了1.2 kb和1.1 kb的转录本。对应于这两种转录本的两个主要转录起始位点分别位于翻译起始位点上游355和226个碱基对处，表明启动子存在交替使用的情况。该基因的5'上游区域包含一个共有序列TGA(A/T)AA(A/G/T)，此序列在主要在幼虫和蛹脂肪体中表达的昆虫基因中已被发现。它还包含三种类似于类固醇受体超家族成员所识别的顺式元件的序列，如鸡卵清蛋白上游启动子转录因子（COUP-TF）/果蝇七上（SVP）、果蝇激素受体39（DHR39）和家蚕分节缺失转录因子1（BmFTZ-F1）。
