Cell proliferation in hematopoiesis

描述（由申请人提供）：细胞增殖的控制是发展的中心主题。在器官形成过程中，细胞分裂的次数是如何受到限制的尚不清楚，但已知的是，控制增殖的机制在人类和果蝇中是保守的。果蝇淋巴腺和血细胞的形成和成熟所必需的大多数基因在人类中是保守的。Toll-NF:B、JAK/STAT、Notch和Ras/Raf等通路调节脊椎动物的造血和果蝇的淋巴腺发育。我们已经发现的一种基因控制着细胞分裂的次数。其蛋白（Zfrp8）与人类蛋白（PDCD2）相似50%。果蝇zfrp8/PDCD2突变体最明显的表型是造血器官淋巴的大量过度生长，伴随着幼虫发育的延迟。我们发现zfrp8通过控制细胞增殖而不是细胞凋亡来调节淋巴腺生长。我们的研究结果表明zfrp8调节果蝇Stat的水平。zfrp8的缺失导致与JAK/STAT通路中功能获得突变相似的表型。PDCD2似乎与人类造血有关，并以两种主要形式存在于人体组织中。在骨髓中，我们检测到一种更大形式的蛋白质，它富含含有干细胞的部分。一种较小形式的蛋白质在白细胞中几乎检测不到。在白血病患者的骨髓和血液中，存在高水平的较小形式的PDCD2。我们计划确定zfrp8在果蝇正常淋巴腺和血细胞发育以及其他组织生长中的作用，并确定其分子功能。我们将使用多种方法寻找与zfrp8一起起作用的其他基因。此外，我们将在脊椎动物中定义PDCD2的基因产物，并将利用血液干细胞和组织培养细胞的体外细胞分化研究它们在人类造血细胞增殖中的功能。

DESCRIPTION (provided by applicant): Control of cell proliferation is a central theme in development. How the number of divisions a cell undergoes during organ formation is limited is not well understood, but it is known that the mechanisms controlling proliferation are conserved in humans and Drosophila. And most genes essential for the formation and maturation of the Drosophila lymph gland and hemocytes are conserved in humans. Pathways such as Toll-NF:B, JAK/STAT, Notch, and Ras/Raf regulate hematopoiesis in vertebrates and lymph gland development in flies. A gene we have identified controls the number of divisions a cell undergoes. Its protein (Zfrp8) is >50% similar to the human protein (PDCD2). The most obvious phenotype of fly zfrp8/PDCD2 mutants is a massive overgrowth of the hematopoietic organ, the lymph gland, accompanied by a delay in larval development. We have found that zfrp8 regulates lymph gland growth by controlling cell proliferation and not apoptosis. Our results suggest that zfrp8 regulates Stat levels in Drosophila. Loss of zfrp8 results in a similar phenotype to gain-of-function mutations in the JAK/STAT pathway. PDCD2 appears to be involved in human hematopoiesis and is present in human tissues in two major forms. In bone marrow we detect a larger form of the protein that is enriched in a fraction containing stem cells. A smaller form of the protein is present in barely detectable amounts in white blood cells. In both the bone marrow and blood of leukemia patients, high levels of the smaller form of PDCD2 are present. We plan to define the role of zfrp8 in Drosophila in normal lymph gland and hemocyte development, and in growth of other tissues and to identify its molecular function. Using a variety of approaches we will search for additional genes functioning with zfrp8. Further, we will define the gene products of PDCD2 in vertebrates, and will investigate their function in cell proliferation in human hematopoiesis using in vitro cell differentiation of blood stem cells and tissue culture cells. PUBLIC HEALTH RELEVANCE: Blood cell development in our model, the fruit fly, is similar in humans, and many of the genes in both humans and fruit flies having to do with blood development are also involved in blood cancers. We have identified a new gene, zfrp8 that if absent, results in flies that show an enormous over-proliferation of blood cells. In humans the same gene is called PDCD2. At least two forms of the PDCD2 protein are present in humans. In bone marrow there is a larger form and in white blood cells we can barely detect a smaller form. We propose a thorough study of how PDCD2/Zfrp8 regulates blood cell formation in flies and to use our findings as a guide to investigate the role of this crucial gene in human blood formation.