Araki Yoshinori, Shimizu Hideki D, Saeki Kentaro, Okamoto Marina, Yamada Lixy, Ishida Kentaro, Sawada Hitoshi, Urushihara Hideko
Graduate School of Life and Environmental Sciences, University of Tsukuba, Tennodai, Tsukuba, Ibaraki, Japan.
Eukaryot Cell. 2012 May;11(5):638-44. doi: 10.1128/EC.00028-12. Epub 2012 Mar 2.
Sexual reproduction is essential for the maintenance of species in a wide variety of multicellular organisms, and even unicellular organisms that normally proliferate asexually possess a sexual cycle because of its contribution to increased genetic diversity. Information concerning the molecules involved in fertilization is accumulating for many species of the metazoan, plant, and fungal lineages, and the evolutionary consideration of sexual reproduction systems is now an interesting issue. Macrocyst formation in the social amoeba Dictyostelium discoideum is a sexual process in which cells become sexually mature under dark and submerged conditions and fuse with complementary mating-type cells. In the present study, we isolated D. discoideum insertional mutants defective in sexual cell fusion and identified the relevant gene, macA, which encodes a highly glycosylated, 2,041-amino-acid membrane protein (MacA). Although its overall similarity is restricted to proteins of unknown function within dictyostelids, it contains LamGL and discoidin domains, which are implicated in cell adhesion. The growth and development of macA-null mutants were indistinguishable from those of the parental strain. The overexpression of macA using the V18 promoter in a macA-null mutant completely restored its sexual defects. Although the macA gene encoded exactly the same protein in a complementary mating-type strain, it was expressed at a much lower level. These results suggest that MacA is indispensable for gamete interactions in D. discoideum, probably via cell adhesion. There is a possibility that it is controlled in a mating-type-dependent manner.
有性生殖对于多种多细胞生物物种的维持至关重要，甚至那些通常进行无性繁殖的单细胞生物也拥有有性周期，因为它有助于增加遗传多样性。关于后生动物、植物和真菌谱系中许多物种受精过程中涉及的分子信息正在不断积累，现在对有性生殖系统的进化研究是一个有趣的课题。社会性变形虫盘基网柄菌中的大囊泡形成是一个有性过程，在这个过程中，细胞在黑暗和淹没条件下性成熟，并与互补交配型细胞融合。在本研究中，我们分离出了在性细胞融合方面存在缺陷的盘基网柄菌插入突变体，并鉴定出了相关基因macA，它编码一种高度糖基化的、含有2041个氨基酸的膜蛋白（MacA）。尽管其整体相似性仅限于盘基网柄菌属内功能未知的蛋白质，但它包含与细胞黏附有关的LamGL和盘状蛋白结构域。macA基因缺失突变体的生长和发育与亲本菌株没有区别。在macA基因缺失突变体中使用V18启动子过表达macA完全恢复了其性缺陷。尽管macA基因在互补交配型菌株中编码的是完全相同的蛋白质，但它的表达水平要低得多。这些结果表明，MacA可能通过细胞黏附对于盘基网柄菌中的配子相互作用是不可或缺的。它有可能是以交配型依赖的方式受到调控的。
