Mechanisms of Maternal Inheritance of Dinoflagellate Symbionts in the Acoelomorph Worm Waminoa litus
Mechanisms of Maternal Inheritance of Dinoflagellate Symbionts in the Acoelomorph Worm Waminoa litus
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DOI：
10.2108/zsj.29.559
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发表时间：
2012-09-01
影响因子：
0.9
通讯作者：
Koike, Kazuhiko
中科院分区：
文献类型：
--
作者：
Hikosaka-Katayama, Tomoe;Koike, Kanae;Koike, Kazuhiko
Waminoa litus 是一种携带虫黄藻的无腔蠕虫，会感染珊瑚。它是双边对称动物的独特之处，因为它通过卵垂直传播其藻类共生体，而不管共生体的异质性如何。它同时拥有两个甲藻属：共生藻属和两栖藻属。在这项研究中，我们使用光学和电子显微镜检查了 W. litus 中藻类共生体的时间和垂直传播途径。线虫的卵子发生可分为三个阶段：第一阶段，卵巢缺失；第二阶段，卵巢消失。第二阶段，早期卵黄形成区，含有卵巢中形成的未成熟卵母细胞；第三阶段，体内有早期和晚期卵黄发生区。在第二阶段的早期卵黄发生区，卵母细胞被辅助卵泡细胞 (AFC) 包围。 Symbiodinium 和 Amphidinium 共生体最初并未在卵母细胞中观察到，但在 AFC 中观察到。在 III 期的卵黄发生晚期区域，卵母细胞被完整的 AFC 鞘包裹；藻类共生体被晚期卵黄卵母细胞吸收。这些观察结果表明 AFC 介导藻类从亲本到卵母细胞的转移。对共生藻共生体的核糖型分析表明，它们与同一实验水族馆中珊瑚所拥有的共生体不同。这些结果表明，W. litus 具有活跃的藻类运输途径，并通过垂直传播维持共生藻的特定谱系。
Waminoa litus is a zooxanthella-bearing acoel worm that infests corals. It is unique to Bilateria in that it transmits its algal symbionts vertically via eggs irrespective of the heterogeneity of the symbionts. It simultaneously harbors two dinoflagellate genera: Symbiodinium and Amphidinium. In this study, we examined the timing and vertical transmission pathway of algal symbionts in W. litus using light and electron microscopy. The oogenesis of the worm can be divided into three stages: stage I, in which the ovary is absent; stage II, the early vitellogenic zone containing immature oocytes formed in the ovary; and stage III, with both early and late vitellogenic zones in the body. In the early vitellogenic zone at stage II, oocytes are surrounded by accessory-follicle cells (AFCs). Both Symbiodinium and Amphidinium symbionts are not initially observed in the oocytes, but are observed in the AFCs. In the late vitellogenic zone at stage III, oocytes are enveloped by a complete sheath of AFCs; the algal symbionts are taken up by the late vitellogenic oocytes. These observations suggest that AFCs mediate the transfer of the algae from the parent to the oocytes. Ribotype analyses of the Symbiodinium symbionts revealed that they differ from those harbored by coral in the same experimental aquarium. These results indicate that W. litus has an active algal transport pathway and maintains a specific lineage of Symbiodinium via vertical transmission.