Investigating FGF/sFRP interactions during forebrain evolution and development

中枢神经系统(CNS)信号中心在胚胎发育过程中对脊椎动物的大脑进行区域化和模式化。这些中枢是诱导附近神经结构的必要条件和充分条件，扰乱信号中枢功能对大脑发育具有灾难性的后果(1-4)。因此，研究调节信号中心活动的发育遗传学机制将增强我们对人类神经发育疾病和障碍背后的遗传异常的理解。由于脊椎动物大脑模式的极其复杂的性质，在更简单的动物中表征同源遗传程序可能为了解大脑发育的基本原理提供新的见解。在无脊椎动物中独一无二的是，半角类动物拥有信号中心，这使得它们适合开发新的假说来解释大脑模式机制。半角类在研究信号中心进化方面也处于特殊的系统发育地位。大脑模式的分子机制是进化的产物，如果不考虑它们的起源，就不能完全理解(5)。除了在大脑发育中的重要作用外，中枢神经系统信号中心也是基因新颖性的首选，这可能促进了早期大脑进化中的形态创新。主要的假说是，中枢神经系统信号中心与复杂的、区域化的大脑共同起源(6，7)。然而，半角兽利用相似的信号中心进行轴向模式的发现表明，脊椎动物的信号中心是通过修改古代分子结构的组件而进化的。此外，半角兽利用两个基因家族之间的相互作用，即FGFs和sFRPs，来调节前部模式。SFRPs和FGFs是前脑诱导和模式形成的关键调节因子，但它们之间的相互作用在脊椎动物中尚未被研究(8-10)。根据表达模式，FGFs和sFRPs可在前神经脊、前脑腹侧和皮质下部相互作用。如果成纤维细胞生长因子/SFRP相互作用发生在这些背景下，那么它们将与新皮质发育的许多方面相关。特殊目标I和II将利用基因敲除、将mRNA注射到卵裂球和半髓状胚胎的胚胎学操作来进一步研究前神经脊的进化起源以及Fgf8/17/18、SFRP1/5和顶端外胚层在前图案形成中的祖先作用。目的III将斑马鱼作为脊椎动物模型来验证fgf3、8和sfrp1a、5之间相互作用调节前脑的规格和模式的假说。这些实验的结果将通过检测潜在目标基因的表达来评估。如果假设的相互作用发生，它们可能提供一种新的机制来整合参与前脑建立和模式形成的两个主要信号通路。

Central nervous system (CNS) signaling centers regionalize and pattern the vertebrate brain during embryogenesis. These centers are necessary and sufficient to induce nearby neural structures, and perturbing signaling center functions has disastrous consequences for brain development (1-4). Accordingly, investigating the developmental genetic mechanisms that mediate signaling center activities will enhance our understanding of genetic anomalies that underlie human neurodevelopmental diseases and disorders. Due to the exceedingly complex nature of vertebrate brain patterning, characterizing homologous genetic programs in simpler animals may provide new insights into basic principles of brain development. Uniquely among invertebrates, hemichordates possess signaling centers, which makes them a suitable group for developing new hypotheses to explain brain patterning mechanisms. Hemichordates are also located in an exceptional phylogenetic position to investigate signaling center evolution. Molecular mechanisms of brain patterning are the products of evolution, and cannot be fully understood without taking their origins into account (5). Beyond their essential roles in brain development, CNS signaling centers are top candidates for genetic novelties that might have facilitated morphological innovations during early brain evolution. The dominant hypothesis is that CNS signaling centers originated in concert with a complex, regionalized brain (6, 7). However, the finding that hemichordates utilize similar signaling centers for axial patterning, suggests that vertebrate signaling centers evolved by modifying components of an ancient molecular architecture. Furthermore, hemichordates utilize interactions between two gene families, FGFs and sFRPs, to mediate anterior patterning. sFRPs and FGFs are critical regulators of forebrain induction and patterning, but interactions between them have not been investigated in vertebrates (8-10). Based on expression patterns, FGFs and sFRPs could interact in the anterior neural ridge, ventral forebrain, and cortical hem. If FGF/sFRP interactions occur in these contexts then they would be relevant to many aspects of neocortical development. Specific Aims I and II will utilize gene knockdowns, mRNA injections into blastomeres, and embryological manipulations of hemichordate embryos to further investigate the evolutionary origins of the anterior neural ridge and ancestral roles of fgf8/17/18, sfrp1/5, and apical ectoderm in anterior patterning. Aim III will utilize the zebrafish as a vertebrate model to test the hypothesis that interactions between fgf3,8 and sfrp1a,5 regulate forebrain specification and patterning. The results of these experiments will be assessed by examining expression of potential target genes. If the hypothesized interactions occur, they could provide a novel mechanism to integrate two major signaling pathways involved in anterior forebrain establishment and patterning.