Cell type-specific roles of Rb in retinal differentiation

描述（由申请人提供）：在视网膜发育过程中，退出细胞周期的决定必须与细胞命运规范和分化精确协调，以确保每种细胞类型的正确比例产生。Rb家族蛋白（Rb、p107和p130）在发育过程中调控细胞周期退出、细胞命运规范、分化和存活。在之前的资助期内，我们专注于Rb家族在小鼠和人类发育过程中调节视网膜祖细胞增殖中的独特和重叠作用。这些研究推动了这一领域的发展，使我们能够开发出首批视网膜母细胞瘤的敲除小鼠模型。我们使用这些和其他视网膜母细胞瘤的临床前模型来测试新的疗法，我们的研究直接影响了St. Jude正在进行的临床试验（RET-5）。在这项拨款申请中，我们将扩展我们之前的研究，并专注于Rb家族在神经元细胞命运规范和分化中的作用。我们的初步数据表明Rb通过不同的机制调节这两个过程。具体来说，我们提出Rb通过抑制Chx10和Pax6启动子上的aE2Fs来调节杆状光感受器细胞命运规范，Rb通过rE2Fs和组蛋白修饰激活Nrl、Nr2e3和Crx启动子来调节杆状光感受器分化。这是肿瘤抑制因子对神经发生如此复杂调控的第一个例子。与杆状光感受器相比，发育中的视网膜中的水平神经元不需要Rb家族来决定细胞命运、迁移或分化。然而，在Rb家族缺失的情况下，成熟的水平细胞重新进入细胞周期并形成转移性视网膜母细胞瘤，同时保持其分化状态。这些数据挑战了发育生物学中广泛持有的观点，即神经元的分化和增殖是不相容的。更重要的是，他们表明依赖Rb进行正常发育的细胞，如杆状光感受器，在Rb家族基因失活后对肿瘤形成有抵抗力，而不依赖Rb家族进行正常发育的细胞，如水平细胞，在Rb家族基因失活后更容易发生肿瘤。我们将在此确定Rb家族在不同细胞类型正常发育过程中的作用是否直接影响其致瘤性。

DESCRIPTION (provided by applicant): During retinal development, the decision to exit the cell cycle must be precisely coordinated with cell fate specification and differentiation to ensure that the correct proportion of each cell type is generated. The Rb family of proteins (Rb, p107 and p130) regulate cell cycle exit, cell fate specification, differentiation and survival during development. In the previous funding period, we focused on the unique and overlapping roles of the Rb family in regulating retinal progenitor cell proliferation during development in mice and humans. These studies moved the field forward and allowed us to develop some of the first knockout mouse models of retinoblastoma. We used these and other preclinical models of retinoblastoma to test new therapies and our research has directly impacted an ongoing clinical trial (RET-5) at St. Jude. In this grant proposal, we will extend our previous studies and focus on the role of the Rb family in neuronal cell fate specification and differentiation. Our preliminary data suggest that Rb regulates these two processes through distinct mechanisms. Specifically, we propose that Rb regulates rod photoreceptor cell fate specification by repressing aE2Fs on the Chx10 and Pax6 promoters and Rb regulates rod photoreceptor differentiation through rE2Fs and histone modification to activate the Nrl, Nr2e3 and Crx promoters. This is the first example of such complex regulation of neurogenesis by a tumor suppressor. In contrast to rod photoreceptors, horizontal neurons in the developing retina do not require the Rb family for cell fate specification, migration or differentiation. However, in the absence of the Rb family, mature horizontal cells re-enter the cell cycle and form metastatic retinoblastoma while maintaining their differentiated state. These data challenge the widely held belief in developmental biology that differentiation and proliferation are incompatible in neurons. More importantly they suggest that cells that rely upon Rb for their normal development such as rod photoreceptors are resistant to tumor formation following Rb family inactivation but cells that do not rely upon the Rb family for their normal development such as horizontal cells are more susceptible to tumorigenesis following Rb family gene inactivation. We will determine here if the role of the Rb family during normal development in different cell types directly influences their susceptibility to become tumorigenic.