Sakurai Toshihide, Lee Hayoung, Kashima Makoto, Saito Yumi, Hayashi Tetsutaro, Kudome-Takamatsu Tomomi, Nishimura Osamu, Agata Kiyokazu, Shibata Norito
Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, Japan.
Int J Dev Biol. 2012;56(1-3):173-82. doi: 10.1387/ijdb.113439ts.
The growth in size of freshwater planarians in response to nutrient intake is limited by the eventual separation of tail and body fragments in a process called fission. The resulting tail fragment regenerates the entire body as an artificially amputated tail fragment would do, and the body fragment regenerates a tail, resulting in two whole planarians. This regenerative ability is supported by pluripotent somatic stem cells, called neoblasts, which are distributed throughout almost the entire body of the planarian. Neoblasts are the only planarian cells with the ability to continuously proliferate and give rise to all types of cells during regeneration, asexual reproduction, homeostasis, and growth. In order to investigate the molecular characteristics of neoblasts, we conducted an extensive search for neoblast-specific genes using the High Coverage Expression Profiling (HiCEP) method, and tested the function of the resulting candidates by RNAi. Disruption of the expression of one candidate gene, DjP2X-A (Dugesia japonica membrane protein P2X homologue), resulted in a unique phenotype. DjP2X-A RNAi leads to an increase of fission events upon feeding. We confirmed by immunohistochemistry that DjP2X-A is a membrane protein, and elucidated its role in regulating neoblast proliferation, thereby explaining its unique phenotype. We found that DjP2X-A decreases the burst of neoblast proliferation that normally occurs after feeding. We also found that DjP2X-A is required for normal proliferation in starved animals. We propose that DjP2X-A modulates stem cell proliferation in response to the nutritional condition.
淡水涡虫因摄入营养而导致的体型生长受到一种名为分裂的过程的限制，在此过程中，尾部和身体片段最终会分离。由此产生的尾部片段会像人工切断的尾部片段一样再生出整个身体，而身体片段则会再生出一条尾巴，从而产生两条完整的涡虫。这种再生能力由多能性体细胞干细胞（称为新生细胞）支持，这些细胞分布在涡虫几乎整个身体中。新生细胞是涡虫中唯一具有持续增殖能力并在再生、无性繁殖、体内平衡和生长过程中产生所有类型细胞的细胞。为了研究新生细胞的分子特征，我们使用高覆盖率表达谱分析（HiCEP）方法广泛搜索新生细胞特异性基因，并通过RNA干扰测试所得候选基因的功能。一个候选基因DjP2X - A（日本三角涡虫膜蛋白P2X同源物）表达的破坏导致了一种独特的表型。DjP2X - A的RNA干扰导致进食后分裂事件增加。我们通过免疫组织化学证实DjP2X - A是一种膜蛋白，并阐明了其在调节新生细胞增殖中的作用，从而解释了其独特的表型。我们发现DjP2X - A减少了进食后通常发生的新生细胞增殖爆发。我们还发现DjP2X - A是饥饿动物正常增殖所必需的。我们提出DjP2X - A根据营养状况调节干细胞增殖。
