Neurogenic plasticity and brain development

我的研究项目的一个长期目标是了解动物在环境中的经历如何影响大脑发育。我的实验室由NSERC资助的研究表明，感觉运动经验，如运动或视觉，在斑马鱼幼体大脑中保持高水平的神经发生。在正常的环境光周期中游动最多的幼虫在随后的几天里表现出大脑发育的加速。相比之下，限制运动或暗淡的光线周期会导致大脑发育减慢。我们观察到，感觉运动剥夺导致神经干细胞(NSCs)经历过早的神经元分化，随着时间的推移，产生的神经元更少。因此，神经干细胞似乎会因感觉运动刺激的改变而改变自己的命运，但这种神经源性可塑性背后的内在机制尚未解决，这也是本研究的重点。神经干细胞的细胞命运决定受到染色质甲基化等表观遗传修饰的强烈影响，而Ehmt2酶是这一过程的关键调节因子，它关闭NSC基因，使干细胞能够分化为神经元。我们利用CRISPR/Cas9基因编辑产生了一个Ehmt2功能缺失突变体，并询问该基因是否需要介导神经干细胞的经验依赖性神经源性可塑性反应。初步数据表明，Ehmt2突变体对运动限制的反应不会改变神经发生，这表明Ehmt2的丢失阻止了大脑中通常由感觉运动剥夺引发的可塑性反应。我们的新突变模型为检验有关神经干细胞命运调控的假说提供了一个范例，同样也为神经干细胞内神经源性可塑性与表观遗传修饰模式之间的联系提供了范例。这项建议的目的是调查运动经历的改变是否会导致胚胎后斑马鱼大脑皮层中的神经干细胞由于NSC基因的表观遗传沉默而改变其命运。以下三个具体的研究目的旨在解决这一目标：目的1：研究Ehmt2功能丧失如何改变经验依赖的神经源性可塑性。遗传谱系追踪将测试突变的神经干细胞是否未能通过增强自我更新而不是促进分化来提供对运动限制的正常可塑性反应。目的：评估神经源性可塑性需要依赖Ehmt2沉默NSC基因表达的程度。我们将询问在正常或运动受限的条件下，Ehmt2的缺失如何导致神经干细胞转录组的变化。目的：探讨Ehmt2基因表达增强对神经源性可塑性的影响。Ehmt2活性的增加将测试当运动增加时，染色质甲基化增强是否会阻止NSCs的扩张，而不是促进分化。这项研究将有助于阐明经验依赖型神经源性可塑性的机制，以便更深入地理解脑发育中基因与环境的相互作用。

A long-term goal of my research program is to understand how an animal's experience in the environment influences brain development. NSERC-funded research from my lab showed that sensorimotor experience, such as movement or vision, maintains high levels of neurogenesis in the zebrafish larval brain. Larvae that swim the most in normal ambient light cycles exhibit increased brain growth over subsequent days of development. In contrast, movement restraint or dim light cycles lead to reduced brain growth. We observed that sensorimotor deprivation resulted in neural stem cells (NSCs) undergoing premature neuronal differentiation, with fewer neurons generated over time. Thus, NSCs appear to change their fate in response to altered sensorimotor stimuli, but the intrinsic mechanism underlying this neurogenic plasticity is unresolved and is the focus of this proposal. Cell fate decisions in NSCs are strongly influenced by epigenetic modifications such as chromatin methylation, and the enzyme Ehmt2 is a key regulator of this process by turning NSC genes off so that stem cells can differentiate into neurons. We generated an Ehmt2 loss of function mutant using CRISPR/Cas9 gene editing and asked whether this gene is required to mediate experience-dependent neurogenic plasticity responses of NSCs. Preliminary data indicates that neurogenesis is not altered in the Ehmt2 mutant in response to movement restraint, suggesting that loss of Ehmt2 prevents the plasticity response in the brain normally elicited by sensorimotor deprivation. Our novel mutant model provides a paradigm for testing hypotheses regarding the regulation of NSC cell fate and likewise for linking neurogenic plasticity to patterns of epigenetic modification within NSCs. The objective of this proposal is to investigate whether an altered movement experience causes NSCs in the postembryonic zebrafish pallium to change their fate due to epigenetic silencing of NSC genes. The following three specific research aims are designed to address this objective: Aim 1: To examine how Ehmt2 loss of function alters experience-dependent neurogenic plasticity. Genetic lineage tracing will test whether mutant NSCs fail to provide a normal plasticity response to movement restraint, by enhancing self-renewal instead of promoting differentiation. Aim 2: To evaluate the degree to which neurogenic plasticity requires Ehmt2-dependent silencing of NSC gene expression. We will interrogate how loss of Ehmt2 leads to transcriptome changes in NSCs under normal or movement restrained conditions. Aim 3: To determine the impact of enhanced Ehmt2 expression on neurogenic plasticity. Increased Ehmt2 activity will test if enhanced chromatin methylation prevents expansion of NSCs when movement is increased, and instead promotes differentiation. This research will help to elucidate mechanisms of experience-dependent neurogenic plasticity for a deeper understanding of gene-by-environment interactions in brain development.