Yuasa Hajime Julie, Kawamura Kazuo, Yamamoto Hiroaki, Takagi Takashi
Laboratory of Biochemistry, Faculty of Science, Kochi University, Kochi, 780-8520, Japan.
J Biochem. 2002 Jul;132(1):135-41. doi: 10.1093/oxfordjournals.jbchem.a003191.
The organization of troponin I (TnI) genes from the ascidian Halocynthia roretzi have been determined. Halocynthia possesses roughly two types of TnI isoforms. One type is a single-copied adult TnI (adTnI) gene, which contains eight exons and seven introns. adTnI expresses two isoforms, the shorter body wall muscle TnI and the longer cardiac TnI, through alternative splicing. The mRNAs of these TnI isoforms may undergo trans-splicing of the 5'-leader sequences, like the TnI mRNA of another ascidian species, Ciona intestinalis. The other type comprises multi-copied larval TnI (laTnI) genes. Halocynthia has at least three laTnIs (alpha, beta, and gamma), which are composed of five exons and four introns, and two of them (alpha and gamma) are clustered in tandem. All laTnIs have B- and M-regions within their 5'-upstream regions, which have been discovered to be the regulatory elements of Halocynthia larval actin genes. The expression of Halocynthia laTnIs and larval actins may be regulated in the same manner. It is known that Ciona does not possess a larva-specific TnI isoform. The phylogenetic tree of ascidian TnIs suggests that laTnIs might have only been generated within the Pleurogona lineage after Enterogona/Pleurogona divergence, and this scenario well agrees with the absence of laTnIs in Ciona.
已经确定了海鞘（Halocynthia roretzi）肌钙蛋白I（TnI）基因的组织结构。海鞘大约有两种类型的TnI同工型。一种类型是单拷贝的成年TnI（adTnI）基因，它包含八个外显子和七个内含子。adTnI通过可变剪接表达两种同工型，较短的体壁肌TnI和较长的心肌TnI。这些TnI同工型的mRNA可能会像另一种海鞘物种（玻璃海鞘，Ciona intestinalis）的TnI mRNA一样，经历5'-前导序列的反式剪接。另一种类型由多拷贝的幼虫TnI（laTnI）基因组成。海鞘至少有三个laTnI（α、β和γ），它们由五个外显子和四个内含子组成，其中两个（α和γ）串联聚集。所有laTnI在其5'-上游区域都有B区和M区，已发现它们是海鞘幼虫肌动蛋白基因的调控元件。海鞘laTnI和幼虫肌动蛋白的表达可能以相同的方式受到调控。已知玻璃海鞘不具有幼虫特异性的TnI同工型。海鞘TnI的系统发育树表明，laTnI可能仅在肠鳃纲/侧鳃纲分化后在侧鳃纲谱系中产生，这种情况与玻璃海鞘中不存在laTnI的情况非常吻合。
