FIBULIN-1 MAINTENANCE OF THE FGF8-DEPENDENT PROXIMAL MANDIBULAR GENETIC PROGRAM

这个子项目是利用资源的许多研究子项目之一。 由NIH/NCRR资助的中心拨款提供。对子项目的主要支持 子项目的首席调查员可能是由其他来源提供的， 包括美国国立卫生研究院的其他来源。为子项目列出的总成本可能 表示该子项目使用的中心基础设施的估计数量， 不是由NCRR赠款提供给次级项目或次级项目工作人员的直接资金。 细胞外基质蛋白，纤维蛋白-1(Fbln1)，已被证明对颅面结构的发育至关重要。事实上，在Fbln1基因缺失的小鼠中观察到的畸形谱与Fbln1在颅神经脊细胞(CNCs)的生长和分化中起到的作用是一致的，CNCs有助于第一臂弓(BA1)结构的形态发生，例如下颌骨。CNCs生长和分化的关键途径尚未完全建立，但已知包括成纤维细胞生长因子8(Fgf8)在内的一些基因是关键基因。Fbln1缺乏的小鼠与Fgf8缺乏的小鼠共享一些重叠的下颌畸形，再加上Fbln1与Fgf8结合的证据，我们推测Fbln1可能参与促进BA1中的Fgf8信号。BA1中Fgf8信号的一个关键方面是Fgf8反应基因的近端激活。其中一个基因是同源结构域转录因子Barx1，它对下颌骨的形成至关重要，并激活Fbln1的表达2。我们发现Fbln1缺陷的小鼠Barx1的表达减少。此外，我们还鉴定了Fbln1基因中两个潜在的Barx1结合位点。根据这一信息，我们提出了一个新的调控模型，在该模型中，Fbln1促进CNCS中的Fgf8-FGFR信号转导，导致Barx1的表达和Fbln1基因的转录激活，从而形成一个正反馈循环。我们推测，这种正反馈系统促进了BA1内CNCs的增殖和分化。为了验证这个模型，有三个特定的目的：1)确定Fbln1缺乏是否导致BA1中Fgf8信号的抑制(即MAPK途径中间产物)；2)确定Fbln1缺乏是否导致下颌形态发生所需的Fgf8反应基因(即Barx1、GSC、Spry1/2和Lhx6)的抑制；以及3)确定Fbln1是否受Barx1转录调控。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The extracellular matrix protein, fibulin-1 (Fbln1), has been shown to be critical for the development of craniofacial structures. Indeed, the spectrum of malformations observed in Fbln1 null mice are consistent with Fbln1 having a role in the growth and differentiation of cranial neural crest cells (CNCs) which contribute to the morphogenesis of structure derived from the first brachial arch (BA1) e.g., the mandible. Pathways key to the growth and differentiation of CNCs have not been fully established, however a number of genes including fibroblast growth factor 8 (Fgf8) are known to be critical. The fact that mice deficient in Fbln1 share some overlapping mandibular malformations with mice deficient in Fgf8, together with evidence that Fbln1 binds Fgf8 has lead us to hypothesize that Fbln1 may be involved in promoting Fgf8 signaling in BA1. A key aspect of Fgf8 signaling in BA1 is the proximal activation of Fgf8 response genes. One such gene is the homeodomain transcription factor, Barx1 which is critical for mandibular formation 12 and activates Fbln1 expression 2. We have found that Fbln1-deficient mice show reduced Barx1 expression. Furthermore, we have identified two potential Barx1 binding sites in the Fbln1 gene. In light of this information, we propose a novel regulatory model in which Fbln1 promotes Fgf8-FgfR signaling in CNCs that leads to the expression of Barx1 and the transcriptional activation of the Fbln1 gene, thus creating a positive feedback loop. We speculate that this positive feedback system promotes the proliferation and differentiation of CNCs within BA1. To test this model there are three specific aims: 1) to determine whether Fbln1 deficiency leads to suppression of Fgf8 signaling (i.e., Map kinase pathway intermediates) in the BA1, 2) to determine whether Fbln1 deficiency leads to suppression of Fgf8 response genes (i.e., Barx1, Gsc, Spry1/2 and Lhx6) required for mandibular morphogenesis, and 3) to determine if Fbln1 is regulated transcriptionally by Barx1.