Regional Differentiation during Forebrain Development

描述（由申请人提供）：我的实验室在该项目之前的资助期内的工作表明，在哺乳动物前脑早期发育过程中，由视黄酸（RA）、成纤维细胞生长因子8 （FGF8）、音刺猬（Shh）和骨形态发生蛋白（BMPs）等局部信号分子介导的间充质/上皮（M/E）诱导对嗅觉通路的形态发生和分化至关重要。我们的观察提出了一个重要的问题：由特定分子信号介导的诱导是如何影响发育中的嗅觉通路中特定细胞类别的身份的？为了解决这个问题，我们将评估在M/E相互作用的背景下，诱导信号分子通过对分子上不同的前体细胞群的作用来调节嗅觉通路神经元的产生和分化的假设。我们将在两个特定目标中对这一假设进行评估：第一个目标包括评估M/E诱导信号在嗅觉上皮中形成嗅觉受体神经元（orn）的前体群体中的机制，第二个目标是研究M/E诱导在建立嗅球中间神经元（OBIs：包括嗅觉颗粒细胞和肾小球周围细胞）前体中的作用。为了实现这些目标，我们已经开发了几种体外检测方法，并辅以体内方法。我们的实验允许我们使用药理学方法或导致每种信号功能丧失或获得的基因突变来操纵通过RA， FGF8， Shh和bmp的信号。利用这些工具，我们将评估通过RA、FGF8和BMP4的信号传导与分子上独特的ORN前体群体的建立以及成熟ORN的功能特性的获得之间的关系。此外，我们将评估通过RA、FGF8、Shh和BMP4的信号在M/E相互作用的背景下对OBI发展的作用。我们将研究信号模式在外侧神经节隆起（LGE）中与OBI前体相关的转录调节因子表达的作用，以及促进OBI前体向初级嗅球的特异性迁移及其初始分化的作用。我们的实验结果将允许我们确定几个基本分子信号的具体贡献，以建立两种细胞类型，这两种细胞类型不仅必须在早期前脑发育期间产生，而且将继续产生并整合到成年前脑中的前体群体的功能回路中。因此，我们的研究结果将表明，在前脑的一个主要功能分支嗅觉通路的初始发育过程中，感应信号是如何作用于定义神经元类别的，以及特定信号如何有助于这些前脑神经元和回路在整个生命过程中的持续再生和修复。

DESCRIPTION (provided by applicant): Work from my laboratory over the previous funding period of this project has shown that mesenchymal/epithelial (M/E) induction, mediated by local signaling molecules including retinoic acid (RA), fibroblast growth factor 8 (FGF8), sonic hedgehog (Shh) and bone morphogenetic proteins (BMPs) is essential for morphogenesis and differentiation of the olfactory pathway during early development of the mammalian forebrain. Our observations raise an essential question: how does induction, mediated by specific molecular signals, influence the identity of specific cell classes in the developing olfactory pathway? To address this question we will evaluate the hypothesis that inductive signaling molecules, acting in the context of M/E interactions, regulate the generation and differentiation of olfactory pathway neurons via their action on molecularly distinct precursor cell populations. We will evaluate this hypothesis in two Specific Aims: the first includes experiments that assess the mechanisms of M/E inductive signaling for establishing precursor populations that give rise to olfactory receptor neurons (ORNs) in the olfactory epithelium, and the second addresses the role of M/E induction in establishing precursors of olfactory bulb interneurons (OBIs: including olfactory granule cells and periglomerular cells). We have developed several in vitro assays, complemented by in vivo approaches, to pursue these aims. Our experiments permit us to manipulate signaling via RA, FGF8, Shh and BMPs using either pharmacological approaches or genetic mutations that result in either loss or gain of function for each signal. Using these tools, we will assess the relationship between signaling via RA, FGF8 and BMP4 and the establishment of molecularly distinct ORN precursor populations as well as the acquisition of functional properties that characterize the mature ORN. In addition, we will evaluate the role of signaling via RA, FGF8, Shh and BMP4 in the context of M/E interaction for OBI development. We will examine the role of signaling patterning the expression of transcriptional regulators associated with OBI precursors in the lateral ganglionic eminence (LGE) as well as facilitating the specific migration of OBI precursors to the rudimentary olfactory bulb as well as their initial differentiation. The results of our experiments will permit us to define the specific contributions of several essential molecular signals to establishing two cell types that must not only be generated during early forebrain development, but that will continue to be generated and integrated into functional circuits from precursor populations that remain in the adult forebrain. Thus, our results will indicate how inductive signals act to define neuronal classes during initial development of a major functional division of the forebrain, the olfactory pathway, as well as how specific signals might contribute to the ongoing regeneration and repair of these forebrain neurons and circuits throughout life.