Vitellogenesis in the sand shrimp, Metapenaeus ensis:: The contribution from the hepatopancreas-specific vitellogenin gene (MeVg2)
Vitellogenesis in the sand shrimp, Metapenaeus ensis:: The contribution from the hepatopancreas-specific vitellogenin gene (MeVg2)
复制标题
DOI：
10.1095/biolreprod.103.022905
复制
发表时间：
2004-09-01
影响因子：
3.6
通讯作者：
He, JG
中科院分区：
文献类型：
--
作者：
Kung, SY;Chan, SM;He, JG
从虾新对虾中克隆并鉴定了结构上与 MeVg1 不同的另一个卵黄蛋白原基因 (MeVg2)。 MeVg2 基因由较少的外显子-内含子组成，很可能是从 MeVg1 基因进化而来的。 MeVg2 的 cDNA 大小为 8.0 千碱基 (kb)，推导的 MeVg2 前体与同一虾的 MeVg1 基因总体上具有 54% 的氨基酸序列同一性。与 MeVg1 前体相比，MeVg2 前体由更多潜在的亚基切割位点组成，表明前体可能被加工成许多更小的亚基。 MeVg2仅在肝胰腺中表达，成年雌性中MeVg2的表达水平从卵黄发生早期开始增加，在卵黄发生中期达到最大值，并在卵黄发生周期末期保持高水平。除了 8-kb mRNA 之外，还鉴定了 MeVg2 的 1.5-2.5 kb 较小转录本，并且 8-kb 转录本仅占整个 MeVg2 衍生转录本的不到 10%。为了确认小转录本的存在，我们筛选了虾肝胰腺 cDNA 文库并分离了两个较小的 MeVg2 特异性 cDNA 克隆。这些克隆与 MeVg2 前体的相应 C 端区域具有超过 99% 的总体同一性，表明 MeVg2 基因发生了替代表达/剪接。通过免疫组织化学分析，卵黄蛋白免疫阳性信号位于肝胰腺的管腔和细胞外部分。组织蛋白和肝胰腺分泌蛋白的氨基酸序列测定表明，76-kDa 卵黄蛋白原亚基很可能被加工成更小的亚基。综上所述，这些结果表明肝胰腺是合成卵黄蛋白原的重要器官，并且可能通过产生大量用于卵巢上调的较小的 MeVg2 亚基来促进卵黄发生。
An additional vitellogenin gene (MeVg2) that is structurally different from MeVg1 was cloned and characterized from the shrimp Metapenaeus ensis. The MeVg2 gene consists of fewer exons-introns and is most likely evolved from the MeVg1 gene. The cDNA for MeVg2 is 8.0 kilobases (kb) in size, and the deduced MeVg2 precursor shared an overall 54% amino sequence identity to the MeVg1 gene of the same shrimp. As compared to the MeVg1 precursor, MeVg2 precursor consists of more potential subunit cleavage sites, suggesting that the precursor may be processed into many smaller subunits. The MeVg2 is expressed only in the hepatopancreas, and the expression level of MeVg2 in adult female increases from the early vitellogenic stage, reaching a maximum at the middle vitellogenic stage, and remains high toward the end of vitellogenic cycle. In addition to the 8-kb mRNA, smaller transcripts of 1.5-2.5 kb for MeVg2 were identified, and the 8-kb transcript only constitutes less than 10% of the overall MeVg2-derived transcripts. To confirm the presence of the small transcripts, we screened the shrimp hepatopancreas cDNA library and isolated two smaller MeVg2-specific cDNA clones. These clones shared greater than 99% overall identity to the corresponding C-terminal region of the MeVg2 precursor, suggesting that an alternative expression/ splicing of the MeVg2 gene occurred. By immunohistochemical analysis, vitellin-immunopositive signals were localized in the lumen and extracellular fraction of the hepatopancreas. Amino acid sequence determination of the tissue protein and secreted protein from the hepatopancreas revealed that the 76-kDa vitellogenin subunit is most likely processed into smaller-sized subunits. Taken together, these results suggest that the hepatopancreas is an important organ for the synthesis of vitellogenin and may contribute to vitellogenesis by producing a large quantity of smaller MeVg2 subunit for ovarian uptakze.