Isoform-specific effects of MeCP2 isoforms on neuronal viability

描述(申请人提供)：自从甲基-CpG结合蛋白2(MeCP2)基因突变被发现是Rett综合征的主要原因以来，人们对了解MeCP2的生物学和正常功能产生了极大的兴趣。MeCP2基因被选择性地剪接以产生通常被称为MeCP2-e1和MeCP2-e2的两个亚型。这两种异构体的意义尚不清楚，人们普遍认为这两种亚型没有功能差异。事实上，大多数异位表达MeCP2的研究并没有具体说明使用的是哪种异构体，而对MeCP2的表达研究很少区分这两者。我们发现，这两种异构体在退化的有丝分裂后神经元中受到不同的调节。此外，MeCP2-e2的表达增强促进了神经元的死亡，而MeCP2-e1的表达增强则没有这种作用。除了差异表达模式和对神经元活性的影响外，这两种异构体结合FoxG1的效率也截然不同。FOXG1是一种促进神经元存活的转录因子，其突变也与Rett综合征有关。该提案的具体目的是(1)了解MeCP2-e2诱导的神经毒性的机制，(2)确定MeCP2和FoxG1在神经元存活调节中的关系，(3)如果时间允许，我们将分析表达MeCP2的转基因小鼠的神经元死亡。值得注意的是，虽然MeCP2和FoxG1蛋白在成熟大脑的神经元中广泛而丰富地表达，但到目前为止，对它们的研究主要集中在它们在神经发育中的作用。我们提议的工作将填补这一空白。如上所述，MeCP2基因在人类中的复制会导致神经功能障碍和小脑神经变性。我们在组织培养模型中观察到的升高的MeCP2-e2的神经毒性作用概括了这种神经退化，并将有助于深入了解其背后的分子机制。 公共卫生相关性：我们的建议重点关注MeCP2，其突变占Rett综合征病例的90%以上，Rett综合征是一种神经发育障碍。虽然已经研究了MeCP2在神经系统发育中的作用，但它在成熟神经元中的功能尚不清楚。此外，脊椎动物中表达的两种不同的MeCP2亚型的功能差异尚不清楚。我们证明了两种MeCP2亚型确实具有不同的功能，包括调节神经元死亡。我们建议研究MeCP2如何调控成熟神经元的死亡，并了解它与FoxG1的关系，FoxG1是另一种与Rett综合征有关的蛋白质。值得注意的是，MeCP2水平升高的人类和小鼠患有一种与雷特综合征不同的神经障碍。除了帮助我们了解神经元如何控制生存和死亡的基本生物学外，我们的研究还可以深入了解MeCP2升高是如何导致人类神经功能障碍的。

DESCRIPTION (provided by applicant): Ever since mutations in the methyl-CpG binding protein 2 (MeCP2) gene were found to be the primary cause of Rett syndrome, there has been a tremendous level of interest in understanding the biology and normal function of MeCP2. The MeCP2 gene is alternatively spliced to generated two isoforms commonly referred to as MeCP2-e1 and MeCP2-e2. The significance of these two isoforms is not known and it is widely believed that there is no functional difference. Indeed, most studies in which MeCP2 is ectopically expressed do not specify which isoforms is being used, and expression studies of MeCP2 rarely distinguish between the two. We find that the two isoforms are differentially regulated in postmitotic neurons that are degenerating. Moreover, the enhanced expression of MeCP2-e2 promotes neuronal death while elevated MeCP2-e1 expression has no such effect. In addition to the differential expression pattern and effect on neuronal viability, the two isofors bind the FoxG1 with dramatically different efficiency. FoxG1 is a transcription factor which promotes neuronal survival and whose mutations have also been linked to Rett syndrome. The specific aims of the proposal are (1) To understand the mechanisms underlying MeCP2-e2-induced neurotoxicity, (2) To define the relationship between MeCP2 and FoxG1 in the regulation of neuronal survival, and (3) If time permits, we will analyze neuronal death in MeCP2-expressing transgenic mice. It is noteworthy that while both MeCP2 and FoxG1 proteins are widely and abundantly expressed in neurons of the mature brain, studies on them have so far focused overwhelmingly on their roles in the context of neurodevelopment. Our proposed work will fill this void. As described above, MeCP2 gene duplication in humans causes neurological dysfunction along with cerebellar neurodegeneration. The neurotoxic effect of elevated MeCP2-e2 that we observe in tissue culture models recapitulates this neurodegeneration and will shed insight into the molecular mechanisms underlying it. PUBLIC HEALTH RELEVANCE: Our proposal focuses on MeCP2, mutations of which account for over 90% of the cases of Rett syndrome, a neurodevelopmental disorder. While the role of MeCP2 during nervous system development has been studied, its function in mature neurons is not clear. In addition, the functional differences of the two different MeCP2 isoforms that are expressed in vertebrate organisms is not known. We show that the two MeCP2 isoforms do have separate functions which include the regulation of neuronal death. We propose to study how MeCP2 regulates the death of mature neurons and understand its relationship with FoxG1, another protein that has been linked to Rett syndrome. It is noteworthy that humans and mice with elevated levels of MeCP2 suffer a neurological disorder distinct from Rett syndrome. Besides helping us understand the basic biology of how the survival and death of neurons is controlled, our studies could shed insight into how elevated MeCP2 causes neurological dysfunction in humans.