Hase Sumitaka, Kashiwagi Emiko, Kobayashi Kazuya, Hoshi Motonori, Matsumoto Midori
Department of Biological Sciences and Informatics, Keio University, Kouhoku, Yokohama, Japan.
Int J Dev Biol. 2007;51(4):345-9. doi: 10.1387/ijdb.062267sh.
The planarian Dugesia ryukyuensis reproduces both asexually (fissiparous) and sexually (oviparous) and can switch from the asexual mode to the sexual mode. By feeding with mature Bdellocephala brunnea oviparous worms, the fissiparous worms, which do not possess sexual organs, can be converted to fully sexualized worms in a process termed sexualization. As sexualization proceeds, the sexual organs are formed uniformly and five stages (stages 15) of the process have been identified histologically. In order to clarify the sexualization process, we attempted to isolate the genes expressed specifically at stage 5 by the differential display method. We isolated five genes expressed in the testis and two genes expressed in the yolk gland, which is an organ specific to sexualized worms. By BLAST search, one of the testis-specific genes was coded as testis-specific alpha-tubulin and two yolk gland-specific genes are similar to ribose-phosphate pyrophosphokinase I and F-box/SPRY-domain protein 1. Drs1, Drs2 and Drs3 were expressed in spermatocytes and spermatids from the early stage of spermatogenesis and Drs4 and Drs5 were expressed in spermatogonia, spermatocytes and spermatids. These genes are useful markers for elucidating the sexualization process.
琉球涡虫既能进行无性生殖（裂殖生殖），也能进行有性生殖（卵生），并且可以从无性生殖模式转变为有性生殖模式。通过喂食成熟的棕色蛭头虫（Bdellocephala brunnea）卵生蠕虫，不具备性器官的裂殖生殖蠕虫可以在一个称为性化的过程中转变为完全性成熟的蠕虫。随着性化过程的进行，性器官均匀形成，并且该过程的五个阶段（1至5阶段）已通过组织学方法确定。为了阐明性化过程，我们尝试通过差异显示法分离在第5阶段特异性表达的基因。我们分离出了五个在睾丸中表达的基因和两个在卵黄腺中表达的基因，卵黄腺是性成熟蠕虫特有的器官。通过BLAST搜索，其中一个睾丸特异性基因编码为睾丸特异性α-微管蛋白，两个卵黄腺特异性基因与核糖磷酸焦磷酸激酶I和F-box/SPRY结构域蛋白1相似。Drs1、Drs2和Drs3在精子发生早期的精母细胞和精子细胞中表达，Drs4和Drs5在精原细胞、精母细胞和精子细胞中表达。这些基因是阐明性化过程的有用标记。
