The Biology of Stem Cells in the Human Parasite Schistosoma Mansoni

 描述(申请人提供)：血吸虫病是一种被忽视的热带疾病，影响着发展中国家的2亿多人。目前只有一种药物(吡喹酮)可用于治疗这种疾病，这突显了旨在了解这些生物的基本生物学过程的研究的重要性。血吸虫病的一个显著特征是引起这种疾病的寄生虫(即血吸虫)可以在 几十年来它们人类宿主的血液流动。这些寄生虫是如何在这种免疫不利的环境中茁壮成长的尚不清楚。为了解决这些寄生虫在哺乳动物宿主中的长寿问题，我们以前证明了血吸虫拥有一群体细胞干细胞，我们称之为新母细胞，能够产生新的肠道和肌肉细胞。我们对这一提议的初步研究让我们发现了一个惊人的现象：这些新生细胞中的很大一部分会分化，产生寄生虫的部分表面涂层，一种被称为被膜的合体组织。我们的数据表明，被盖细胞迅速翻转，依靠新生母细胞进行持续更新。其结果是，在干细胞耗尽后的几天内，许多与被膜相关的分子的表达大幅下调。由于被层是寄生虫和宿主之间的主要界面，了解干细胞-被层关系将为血吸虫如何防御免疫攻击提供重要线索。基于这些观察，我们推测新生细胞的一个重要功能是迅速再生寄生虫的被膜，从而确保宿主-寄生虫界面的功能和逃避宿主免疫。为了解决这一假设，我们提出了以下两个具体目标：(1)发现新胚细胞到被膜转变的调节因子；(2)了解新生细胞在体内维持被层功能中的作用。在第一个目标中，我们将使用转录图谱和原位杂交来鉴定在血吸虫干细胞中表达的基因。然后，我们将使用RNA干扰来确定这些基因中的哪些是新生细胞分化为被细胞所必需的。在第二个目标中，我们将使用电子显微镜和免疫学方法相结合的方法来确定新生细胞消融对被膜形态和功能的影响。同时，我们将通过手术将不能制造新的外皮细胞的寄生虫移植到小鼠体内，并检查对蠕虫存活的影响。这些研究具有创新性，因为它们是第一次探索新生母细胞在这种毁灭性寄生虫的生物学中的功能，并为研究这些生物体带来了许多新的方法。总的来说，这些研究将确定新生母细胞如何在宿主免疫系统的背景下促进寄生虫的生存，可能导致针对这些重要病原体的新的治疗方法。

 DESCRIPTION (provided by applicant): Schistosomiasis is a neglected tropical disease that affects more than 200 million people in the developing world. Currently only a single drug (praziquantel) is available to treat this disease, highlighting the importance of studies aimed at understanding basic biological processes in these organisms. One remarkable characteristic of schistosomiasis is that the parasites responsible for this disease (i.e., schistosomes) can live in the blood stream of their human hosts for decades. How these parasites thrive in this immunologically hostile environment is not known. To address the longevity of these parasites in their mammalian host we previously demonstrated that schistosomes possess a population of somatic stem cells, which we refer to as neoblasts, which are capable of generating new intestine and muscle cells. Our preliminary studies for this proposal led us to a striking observation: a large fraction of these neoblasts differentiate to produce parts of the parasite's surface coat, a syncytial tissue known as the tegument. Our data suggest that tegumental cells are rapidly turned over, relying on neoblasts for their continuous renewal. As a result, many tegument-associated molecules are drastically down regulated within days following stem cell depletion. Since the tegument is the primary interface between the parasite and its host, understanding the stem cell-tegument relationship will provide important clues about how schistosomes defend themselves from immune attack. Based on these observations, we hypothesize that an important function of the neoblasts is to rapidly regenerate the parasite's tegument, thereby ensuring a functional host-parasite interface and evasion of host immunity. To address this hypothesis we propose the following two specific aims: (1) discover regulators of the neoblast-to-tegument transition and (2) understand the role for neoblasts in maintaining tegumental function in vivo. In the first aim, we will use transcriptional profiling and in situ hybridization to identify genes expressed in schistosome stem cells. We will then use RNA interference to determine which of these genes are required for the differentiation of the neoblasts into tegumental cells. In the second aim, we will use a combination of electron microscopy and immunological approaches to determine the effects that neoblast ablation has on tegumental morphology and function. Concurrently, we will surgically-transplant parasites incapable of making new tegumental cells into mice and examine the effects on worm survival. These studies are innovative as they are the first to explore the function of the neoblasts in the biology of this devastating parasite and bring a number of new methodologies to the table for studying these organisms. Collectively, these studies will determine how neoblasts contribute to parasite survival in the context of the host immune system, potentially leading to new therapeutic approaches targeting these important pathogens.