Functional genomic characterization of germinal cells in larval Schistosoma mansoni

RNA-seq experiments to identify gene expression changes following miracidia to sporocyst transformation in Schistosoma mansoni.Schistosomes infect hundreds of millions of people in the developing world. Transmission of these parasites relies on a stem cell-driven, clonal expansion of larvae inside a molluscan intermediate host. How this novel asexual reproductive strategy relates to current models of stem cell maintenance and germline specification is unclear. Here, we demonstrate that this proliferative larval cell population (germinal cells) shares some molecular signatures with stem cells from diverse organisms, in particular neoblasts of planarians (free-living relatives of schistosomes). We identify two distinct germinal cell lineages that differ in their proliferation kinetics and expression of a nanos ortholog. We show that a vasa PL10 homolog is required for proliferation and maintenance of both populations; whereas, argonaute2 and a fibroblast growth factor receptor-encoding gene are required only for nanos-negative cells. Our results suggest that an ancient stem cell-based developmental program may have enabled the evolution of the complex life-cycle of parasitic flatworms.

本数据集通过RNA测序（RNA-seq）实验，以鉴定曼氏血吸虫（Schistosoma mansoni）毛蚴（miracidia）向胞蚴（sporocyst）转化过程中的基因表达变化。血吸虫在发展中国家感染数亿人口，其传播依赖于在软体动物中间宿主体内，由干细胞驱动的幼虫克隆扩增过程。目前，这种全新的无性生殖策略与现有干细胞维持及生殖系特化模型之间的关联尚不明确。本研究证实，这种具有增殖能力的幼虫细胞群（生殖源性细胞（germinal cells））与多种生物的干细胞存在部分分子特征的共通性，尤其与曼氏血吸虫的自由生活近亲——涡虫的成体干细胞（neoblasts）高度相似。我们鉴定出两类截然不同的生殖源性细胞谱系，二者在增殖动力学及nanos同源基因的表达模式上存在差异。研究表明，vasa PL10同源基因对两类细胞群的增殖与维持均不可或缺；而Argonaute2及成纤维细胞生长因子受体编码基因仅在nanos阴性细胞群的维持中发挥作用。本研究结果提示，一套基于干细胞的古老发育程序，可能助力了寄生扁形动物复杂生活史的演化。