Hedgehog, Patched, and Gli in Medulloblastoma

描述（申请人提供）：脑肿瘤是儿童癌症死亡的头号原因，髓母细胞瘤是最常见的恶性脑肿瘤。包括分泌因子Sonic Hedgehog （Shh）和下游基因patch （Ptc）和Gli在内的信号通路在大脑发育，特别是小脑的发育中起着关键作用。由浦肯野细胞释放的Shh可缓解ptc介导的细胞生长抑制并促进颗粒细胞前体的增殖。颗粒细胞在发育过程中先在小脑外颗粒层（EGL）增殖，然后退出细胞周期，沿径向胶质纤维向内迁移至内颗粒层（IGL）。髓母细胞瘤被认为起源于颗粒细胞前体。最近的研究表明，Shh通路组分的突变与人类成神经管细胞瘤有关。此外，大约15%的Ptc突变杂合小鼠在6-12月龄时发生成神经管细胞瘤。我们已经证明Shh在小鼠胚胎和出生后小脑中的错误表达会产生肿瘤。我们的总体目标是探索激活Sonic Hedgehog通路导致成神经管细胞瘤形成的机制。我们将进一步开发和表征一种小鼠髓母细胞瘤模型，其中Shh在胚胎小脑中错误表达，通过超声引导注射将逆转录病毒载体引入胚胎脑。Ptc和Gli1的参与将通过以下方法确定：1)我们将描述sh -信号通路的激活如何在野生型小鼠中维持一些早期EGL颗粒神经元处于增殖、未分化状态，并诱导成神经管细胞瘤的形成；2)我们将测试Ptc零突变杂合小鼠中sh -信号通路的激活是否会导致协同效应，加速和/或更高的肿瘤发生频率；3)我们将通过向Gli1-/-和Gli3+/-突变体注射sh -逆转录病毒来测试肿瘤形成是否需要Shh在下游，Gli3的杂合性是否能促进肿瘤形成。

DESCRIPTION (provided by applicant): Brain tumors are the number one cause of cancer death in children and medulloblastoma is the most common malignant brain tumor. The signaling pathway involving the secreted factor Sonic Hedgehog (Shh) and the downstream genes Patched (Ptc) and Gli play critical roles in brain development, particularly that of the cerebellum. Shh, released by Purkinje cells, relieves Ptc-mediated repression of cell growth and promotes proliferation of granule cell precursors. Granule cells undergo proliferation in the external granule layer (EGL) of the cerebellum during development, then exit the cell cycle and migrate inwardly along radial glia fibers to the internal granule layer (IGL). Medulloblastoma is thought to arise from a granule cell precursor. Recent studies have demonstrated that mutations in components of the Shh pathway are associated with medulloblastoma in humans. Furthermore, approximately 15% of mice heterozygous for a Ptc mutation develop medulloblastoma at 6-12 months of age. We have shown that mis-expression of Shh in the mouse embryonic and postnatal cerebellum produces tumors. Our overall aim is to explore the mechanism by which activation of the Sonic Hedgehog pathway leads to medulloblastoma formation. We will further develop and characterize a mouse model of medulloblastoma in which Shh is mis-expressed in the embryonic cerebellum using a retroviral vector introduced into the embryonic brain by ultrasound-guided injection. The involvement of Ptc, and Gli1 will be determined by the following approaches: 1) we will characterize how activation of the Shh-signaling pathway maintains some early EGL granule neurons in a proliferative, undifferentiated state and induces medulloblastoma formation in wild type mice, 2) we will test whether activation of the Shh-signaling pathway in mice heterozygous for a null mutation in Ptc results in a synergistic effect, with accelerated and/or a higher frequency of tumorigenesis, and 3) we will test whether Gli1 is required downstream of Shh for tumor formation and whether heterozygosity for Gli3 enhances tumor formation by injecting Shh-retrovirus into Gli1-/- and Gli3+/- mutants. This system provides a unique opportunity to investigate an in vivo animal model of childhood medulloblastoma, and to determine the roles of Ptc and Gli in tumorigenesis.