An exhaustive exploration of the genes involved in molluscan shell formation : a primer for a genome projec

在本研究中，我们旨在通过表征(1)外壳形成的主控基因(2)控制外壳的蛋白质（生物矿化）和(3)控制外壳左右不对称的沉淀基因来阐明外壳的进化过程和机制，并获得以下结果。(1)转录因子engrailed和生长因子dpp的基因表达模式表明，engrailed和其他软体动物一样在壳腺周围表达，而dpp只在内陷壳腺的右侧表达，说明这两个基因都参与了壳的形成，dpp可能是壳左右不对称的进一步原因。(2)生物矿化基因对8种肺螺壳基质蛋白皮桥蛋白的系统发育分析表明，导致壳基质蛋白进化的基因复制在肺螺中至少独立发生了2次。与化石记录的比较表明，这些重复应该发生在中生代之后。在珍珠贝fucata Pinctada中，推导出了异常酸性壳基质蛋白Aspein的初级结构。表达模式和体外功能分析表明，Aspein很可能是fucata中方解石壳选择性沉淀的控制因子。(3)壳左右不对称的控制基因我们利用HiCEP方法对停滞淋巴（lynnaea heinalis）中左右侧套上皮表达模式不对称的mrna进行了详尽的分析，发现在套上皮中共有11588个基因表达，其中数十个基因表现出左右不对称的基因表达模式。对20个表明不对称程度最高的基因的结构和功能的分析仍在进行中。

In this study, we aimed at elucidating the evolutionary processes and mechanisms of the shell by characterizing the (1) master genes shell formation, (2) proteins controlling shell (biomineralization), and (3) control precipitation genes for the shell left-right asymmetry, and obtained the following results.(1) master genes for shell formation Gene expression patterns of the transcription factor engrailed and the growth factor dpp in Lymnaea stagnalis indicated that engrailed is expressed around the shell gland just like in other molluscs, and dpp is expressed only in the right-hand side of the invaginated shell gland, suggesting that both genes are involved in shell formation and dpp could be further responsible for the shell left-right asymmetry.(2) biomineralization genes Phylogenetic analysis of the shell matrix protein Dermatopontin among eight species of pulmonate snails showed that the gene duplications that lead to the evolution of the shell matrix proteins occurred at least twice independently in pulmonates. Comparisons with the fossil record indicated that these duplications should have occurred after Mesozoic Era. In the pearl oyster Pinctada fucata, the primary structure of the unusually acidic shell matrix protein Aspein has been deduced. Analyses of expression patterns and in vitro functions demonstrated that Aspein is highly likely the factor controlling the selective precipitation of calcite shells in P. fucata.(3) control genes for the shell left right asymmetry We performed an exhaustive analysis using the HiCEP method for the mRNAs that show asymmetric expression patterns between the right-hand side and the left-hand side of the mantle epithelium in Lymnaea stagnalis, and found that a total of 11588 genes are expressed in the mantle and that dozens of genes show a left-right asymmetric gene expression pattern. Analysis is still on progress as to the structure and function for the 20 genes that indicated the highest extent of asymmetry.