Molecular Mechanisms for Maintaining Stem Cell Immaturity

为了揭示干细胞的分子基础，我们分析了三个基因的功能，发现它们都是生殖系干细胞系统所必需的。1）我们分析了肿瘤抑制基因PTEN（来自染色体10的磷酸酶和张力蛋白同源物）的功能。PTEN是P13激酶的负调控因子，其磷酸酶活性催化PIP 3转化为PIP 2。我们制备了原始生殖细胞（PGC）特异性靶向的小鼠PTEN。PGC特异性PTEN缺失小鼠在所有新生雄性小鼠中显示畸胎瘤形成。2）我们克隆了果蝇生殖细胞发育所必需的一个小鼠同源基因，该基因与果蝇PGC形成有关。为了分析该基因（小鼠生殖细胞less-1，mgcl-1）的功能，制备了基因打靶小鼠。小鼠在PGC形成中未显示任何异常。然而，靶向小鼠的生育能力显著降低。在研究过程中，有报道称mgcl-1蛋白与核膜的一种成分LAP 2 β结合，这促使我们研究精子发生过程中的核形态。Piwi基因是果蝇生殖细胞自我更新所必需的基因。我们克隆了一个小鼠同源基因mili，并通过基因打靶分析其功能。mili基因敲除小鼠由于初级精母细胞粗线期凋亡而不能产生精子，这些结果有助于理解干细胞在生殖系统中的分子机制。

To reveal the molecular basis of stem cells, we analyzed the function of three genes and found that all of them are essential for germ line stem cell systems.1) We analyzed the function of a tumor suppressor gene PTEN (phosphatase and tensin homologue from chromosome 10). PTEN is a negative regulator of P13kinase by its phosphatase activity catalyzing from PIP3 to PIP2. We produced primordial germ cell (PGC) specific PTEN targeting mouse. The PGC specific PTEN null mice showed teratoma formation in all new born male mice. And the in vitro proliferative activity and embryonic germ cell forming activity was strikingly increased in the null mice.2) We cloned a mouse homologue of Drosophila germ cell less gene which is essential for PGC formation in the fly. To analyze the function of the gene (mouse germ cell less-1, mgcl-1), gene targeting mice were produced. The mice did not show any abnormality in PGC formation. However, the fertility of the targeting mice was significantly reduced. During the study, it was reported that mgcl-1 protein binds to a component of nuclear envelope, LAP2β, which prompted us to examine the nuclear morphology in spermatogenesis. Nuclear morphology of the null spermatocyte was abnormal and subsequent chromatin remodeling was impaired.3) Piwi is a gene essential for germ cell self renewing activity in Drosophila. We cloned one mouse homologue, mili, and analyzed its function by gene targeting. The mili null mice could not produce sperm due to apoptotic cell death at pachytene phase of primary spermatocytes.All of the results facilitates the understanding of molecular mechanisms of stem cells in germ system.