Roles of engrailed proteins in granule cells during cerebellum development

描述（由申请人提供）：小脑是位于后脑上方的脑后部结构，负责协调运动和认知功能。在这个提案中，我的目标是确定负责小脑发育不全的细胞和分子机制，这是由于从发育中的小脑外生发层（EGL）的颗粒细胞祖细胞（gcp）中去除EN1和EN2（合称为EN1/2）的EN1和EN2同源盒转录因子（EN）。由于在这些突变体中没有检测到主要的细胞结构缺陷，因此必须存在其他细胞类型的细胞非自主稳态缩放，以补偿所产生的颗粒神经元种群的减少。在一个器官内适当数量和位置的细胞类型的规范是生物系统发展的一个关键挑战，无论是该器官的内在功能还是该器官在整个生物体中的运作。在神经系统中，神经元亚型群体大小的变化可以影响突触后和突触前神经元的规格或存活，这一效应首先由维克多·汉堡和丽塔·列维-蒙塔尔奇尼发现的经典神经营养假说证明。在许多疾病（如小头畸形、精神分裂症和自闭症谱系障碍）中观察到脑亚区大小的变化，特别强调了大小调节在神经发育中的重要性。该研究包括两个主要目的：1)确定EN1/2在Cb的GCPs中调控的细胞过程和EN1/2突变GCPs对主要有丝分裂原Sonic Hedgehog （SHH）的响应性；2)鉴定EN2直接DNA结合序列和受EN1/2调控的相关基因，这些基因是EN1/2调控Cb发育过程中GCP行为的下游效应体。

DESCRIPTION (provided by applicant): The cerebellum is a posterior brain structure located above the hindbrain that coordinates motor and cognitive function. In this proposal, I aim to determine the cellular and molecular mechanism responsible for the cerebellar hypoplasia that results from removal of the engrailed (EN) homeobox transcription factors EN1 and EN2 (refered to together as EN1/2) from granule cell progenitors (GCPs) in the external germinal layer (EGL) of the developing cerebellum (Cb). Since major cytoarchitectural defects are not detected in these mutants, there must be cell non-autonomous homeostatic scaling of other cell types to compensate for the reduced granule neuron population generated. Specification of cell types in appropriate number and position within an organ represents a key challenge in development of biological systems, both for the intrinsic function of that organ and with regards to operation of that organ within the whole organism. In neural systems, changes in the population size of neuron subtypes can affect specification or survival of post- and presynaptic neurons, an effect first demonstrated by the now classic neurotrophic hypothesis discovered by Viktor Hamburger and Rita Levi-Montalcini. The importance of size regulation in neural development is particularly emphasized by the observation of changes in brain subregion size in numerous diseases, such as microcephaly, schizophrenia and autism spectrum disorder. The proposed study involves two major aims: 1) determine the cellular processes regulated by EN1/2 in GCPs of the Cb and the responsiveness of EN1/2 mutant GCPs to the major mitogen Sonic Hedgehog (SHH); and 2) identify EN2 direct DNA binding sequences and associated genes regulated by EN1/2 that are downstream effectors of EN1/2 regulated GCP behaviors in the developing Cb. PUBLIC HEALTH RELEVANCE: The cerebellum is a brain structure involved in motor control and cognition in humans, and contains the most abundant neuronal subtype in the vertebrate brain, the cerebellar granule cell. Studies in mice have demonstrated that the engrailed family of homeodomain transcription factor proteins (EN1 and EN2) regulates multiple aspects of cerebellar development including growth, morphology, gene expression patterning, and neural circuit formation. In humans, the EN1/2 genes have been implicated in Parkinson's disease, autism spectrum disorder, and likely also are critical for many aspects of cerebellar development. This proposal will utilize mouse genetics and genomics approaches to determine the roles EN1/2 play in granule cells to ensure proper cerebellum growth and circuit formation, as well as identify downstream genes that carry out these functions.