Uncharacterized genes in S. japonicum.

Schistosomiasis affects more than 250 million people worldwide and is one of the neglected tropical diseases. Currently, the treatment of schistosomiasis relies on a single drug-praziquantel-which has led to increasing pressure from drug resistance. Therefore, there is an urgent need to find new treatments. The development of genome sequencing has provided valuable information for understanding the biology of schistosomes. In the genome of Schistosoma japonicum, approximately 11% of the protein-coding sequences are uncharacterized genes (UGs) annotated as “hypothetical protein” or “protein of unknown function.” These poorly understood genes have been unjustifiably neglected, although some may be essential for the survival of the parasites and serve as potential drug targets. In this study, we systematically mined the highly expressed UGs in both genders of this parasite throughout key developmental stages in their mammalian host, using our previously published S. japonicum genome and RNA-seq data. By employing in vitro RNA interference (RNAi), we screened 126 UGs that lack homologs in Homo sapiens and identified 8 that are essential for the parasite vitality. We further investigated two UGs, Sjc_0002003 and Sjc_0009272, which resulted in the most severe phenotypes. Fluorescence in situ hybridization demonstrated that both genes were expressed throughout the body without sex bias. Silencing either Sjc_0002003 or Sjc_0009272 reduced the cell proliferation in the body. Furthermore, in vivo RNAi indicated both genes are required for the growth and survival of the parasites in the mammalian host. For Sjc_0002003, we further characterize the underlying molecular cause of the observed phenotype. Through RNA-seq analysis and functional studies, we revealed that silencing Sjc_0002003 reduces the expression of a series of intestinal genes, including Sjc_0007312 (hypothetical protein), Sjc_0008276 (vha-17), Sjc_0002942 (PLA2G15), and Sjc_0003646 (SJCHGC09134 protein), leading to gut dilation. Our work highlights the importance of UGs in schistosomes as promising targets for drug development in the treatment of the schistosomiasis.

血吸虫病（Schistosomiasis）在全球范围内影响超过2.5亿人口，属于被忽视的热带病之一。目前，血吸虫病的治疗仅依赖吡喹酮（praziquantel）这一种药物，由此带来了日益严峻的耐药性压力，因此亟需开发新型治疗方案。基因组测序技术的发展为解析血吸虫的生物学特性提供了宝贵信息。在日本血吸虫（Schistosoma japonicum）的基因组中，约11%的蛋白编码序列为未注释功能基因（uncharacterized genes，UGs），被标注为"假设蛋白（hypothetical protein）"或"功能未知蛋白（protein of unknown function）"。这类认知匮乏的基因长期遭到不合理的忽视，尽管其中部分可能对寄生虫的存活至关重要，可作为潜在药物靶点。本研究依托已发表的日本血吸虫基因组与RNA测序（RNA-seq）数据，系统挖掘了该寄生虫在哺乳动物宿主内关键发育阶段的雌雄两性高表达未注释功能基因。通过体外RNA干扰（RNA interference，RNAi）实验，我们筛选出126个在智人（Homo sapiens）中无同源序列的未注释功能基因，并鉴定出8个对寄生虫活力不可或缺的基因。我们还针对两种表型影响最为显著的未注释功能基因Sjc_0002003与Sjc_0009272开展了深入研究。荧光原位杂交（fluorescence in situ hybridization）实验证实，这两种基因在虫体全身均有表达，且无性别偏好。沉默Sjc_0002003或Sjc_0009272均可降低虫体内的细胞增殖水平。此外，体内RNA干扰实验表明，这两种基因对寄生虫在哺乳动物宿主内的生长与存活均必不可少。针对Sjc_0002003，我们进一步解析了其引发观测表型的潜在分子机制。通过RNA测序分析与功能实验，我们发现沉默Sjc_0002003会下调一系列肠道相关基因的表达，包括Sjc_0007312（假设蛋白）、Sjc_0008276（vha-17）、Sjc_0002942（PLA2G15）以及Sjc_0003646（SJCHGC09134蛋白），最终导致肠道扩张。本研究凸显了血吸虫未注释功能基因的重要价值，其有望成为血吸虫病治疗药物开发的潜在靶点。