Germ cell specifications and differentiation in planarians.

描述（由申请人提供）：生殖细胞作为世代之间的纽带，产生配子，将遗传物质从亲本传递给后代。了解生殖细胞发育的机制将有助于阐明全能性的本质、不育的原因和生殖细胞肿瘤的起源。生殖细胞发育的许多知识来自于研究利用细胞质决定因素来确定早期胚胎发生中生殖细胞命运的模式生物。相比之下，许多生物（包括哺乳动物）利用感应信号来指定生殖细胞在发育后期的命运。尽管存在这些差异，由决定因素指定的生殖细胞和诱导形成的生殖细胞具有一些共同的内在机制，包括体细胞命运的转录抑制和基因表达的转录后控制。诱导生殖细胞发育的机制研究几乎仅限于小鼠，重要的问题仍未得到解答。例如，什么样的转录网络定义和维持生殖细胞的命运？在确定了生殖细胞后，哪些系统因素将其进一步分化与动物的生理状态联系起来？淡水涡虫地中海施米德（Schmidtea mediterranea）是研究这些问题的有力模型。它具有惊人的再生能力，基于成体干细胞群，即使是微小的身体碎片也能再生完整的个体。在涡虫中，生殖细胞系在胚胎后由体细胞干细胞发育而来；像体细胞一样，生殖细胞谱系也可以再生。申请人实验室产生的初步数据已经确定了维持生殖细胞和调节其分化所需的内在和外在调节因子。基于这些数据，将追求两个具体目标：(i)表征早期生殖细胞中的转录网络；（ii）剖析以神经肽为基础的生殖细胞分化系统调控。

DESCRIPTION (provided by applicant): Germ cells serve as a link between generations, producing gametes that propagate genetic material from parent to offspring. Understanding the mechanisms by which germ cells develop will help illuminate the nature of totipotency, the causes of infertility, and the origins of germ cell tumors. Much knowledge of germ cell development derives from studying model organisms that utilize cytoplasmic determinants to specify germ cell fate in early embryogenesis. In contrast, many organisms (including mammals) utilize inductive signals to specify germ cell fate later in development. In spite of these differences, germ cells specified by determinants and those formed inductively share several common intrinsic mechanisms, including transcriptional repression of somatic fates and post-transcriptional control of gene expression. Mechanistic studies of inductive germ cell development have been limited almost exclusively to mouse and important questions remain unanswered. For example, what transcriptional networks define and maintain germ cell fate? After a germ cell has been specified, what systemic factors link its further differentiation with te physiological status of the animal? The freshwater planarian, Schmidtea mediterranea, serves as a powerful model for studying these questions. It has prodigious regenerative abilities, based upon a population of adult stem cells that allow even tiny body fragments to regenerate complete individuals. In planarians, the germ cell lineage develops post- embryonically from the somatic stem cells; like the soma, the germ cell lineage can also be regenerated. Preliminary data generated in the applicant's laboratory have identified intrinsic and extrinsic regulators required for maintaining germ cells and for regulating their differentiation. Based on these data, two specific aims will be pursued: (i) to characterize the transcriptional network in early germ cells; and (ii) to dissect the neuropeptide-based systemic regulation of germ cell differentiation. Work performed under the first aim will use chromatin immuno-precipitation, next-generation sequencing, and computational approaches to identify targets of a germ cell-specific transcription factor required for maintaining early germ cells. Experiments conducted under aim two will characterize the neuropeptide receptor mediating the systemic regulation of germ cell development, identify the cell type(s) that express the receptor, and discover genes expressed in response to neuropeptide signaling. For both aims, the functional genomic tools for studying S. mediterranea (high- throughput in situ hybridization; RNA interference by feeding double-stranded RNA) will be used to validate target genes and determine their functions. These studies use a model organism with unique attributes, and take unbiased, genomic approaches to identify conserved factors; thus, they have great potential to innovate. This work is significan because of its potential: (i) to identify conserved genes required for proper germ cell development; and (ii) to provide a promising strategy for understanding and treating parasitic flatworms that infect hundreds of millions of people worldwide. PUBLIC HEALTH RELEVANCE: Germ cells give rise to the next generation by producing gametes (eggs and sperm). Studying how these cells are produced and regulated is relevant to understanding potential causes of infertility in humans and the cancers that result from inappropriate regulation of germ cells. This research uses the planarian to understand how germ cells develop because it is relatively easy to identify genes and study their functions in thi simple animal; analyzing genes shared between planarians and mammals will help us figure out how these genes function in mammalian germ cells.