Identification and characterization of FGF target genes

为了解决我们对哪些基因响应FGF信号传导的知识不足，我们 有一个正在进行的项目，以分子定义FGF靶基因，以及他们的功能， 调控在过去的工作中，我们和其他人已经确定了转录因子编码的 Gbx1和Gbx2作为FGF靶点。最近，我们研究了Gbx与 使用组合Gbx小鼠突变体在发育中的脊髓中观察家族成员。我们展示 如果另一个基因缺失，每个Gbx基因都会上调。此外，Gbx基因调节 PAX2+背侧抑制性中间神经元亚群的发育。此外，扩大 在Gbx突变体中发生了将增殖细胞引入解剖学上限定的套层区的情况。最后， 我们的数据显示Gbx腹侧脊髓中凋亡细胞死亡显著增加， 突变体在胚胎中期。虽然我们的研究表明，Gbx的两个成员 基因家族参与PAX2+背侧中间神经元亚群的发育和存活 在腹侧运动神经元中，Gbx1和Gbx2不足以在遗传上补偿 彼此的失落。因此，我们的研究提供了新的见解的关系， Gbx1和Gbx2在脊髓发育中的作用（J Dev Biol.2020. PMID：32244588）。在 目前的工作，我们证明了Hes7转录抑制因子可能是一个直接的目标， FGF4信号传导。在脊椎动物的发育过程中，有体前中胚层（presomitic mesoderm，PSM） 分节为体节，体节将形成分节的脊柱和相关的肌肉， 结缔组织和真皮。体节发生的周期性受体节的调节 振荡Notch活动的时钟。我们检测了仅缺乏Fgf4或Fgf8的小鼠突变体， 我们先前证明了其冗余地阻止PSM分化。FGF8不是 Fgf4突变体是体节发生所必需的，但Fgf4突变体显示出一系列椎骨缺陷。分析 基因表达与荧光标记的mRNA的基于空间模型的定量 杂交链反应，我们表明，FGF4控制Notch途径振荡，通过 转录抑制因子HES7我们支持这一假设，通过证明一个遗传 Hes7和Fgf4之间的协同作用，但不与Fgf8。因此，我们确定FGF4是一种必需的 陷波振荡调节器和潜在的重要的人类分割的频谱 由缺陷性Notch振荡引起的椎骨缺陷。（eLife 2020年11月19日; 9：e55608. doi：10.7554/eLife.55608.）未来的工作将集中在什么样的监管要素在他7 基因对FGF4信号有反应。

To address the deficiency in our knowledge of what genes respond to FGF signaling, we have an ongoing project to molecularly define FGF targets genes, as well as their function and regulation. In past work, we and others have identified the transcription factors encoded by Gbx1 and Gbx2 as FGF targets. Recently we investigated the functional relationship between Gbx family members in the developing spinal cord using combinatorial Gbx mouse mutants. We showed that each Gbx gene is upregulated if the other is absent. Additionally, Gbx genes regulate development of a subset of PAX2+ dorsal inhibitory interneurons. Also, expansion of proliferative cells into the anatomically defined mantle zone occurs in Gbx mutants. Lastly, our data shows a marked increase in apoptotic cell death in the ventral spinal cord of Gbx mutants during mid-embryonic stages. While our studies reveal that both members of the Gbx gene family are involved in development of subsets of PAX2+ dorsal interneurons and survival of ventral motor neurons, Gbx1 and Gbx2 are not sufficient to genetically compensate for the loss of one another. Thus, our studies provide novel insight to the relationship harbored between Gbx1 and Gbx2 in spinal cord development (J Dev Biol. 2020. PMID: 32244588). In current work, we demonstrate that the Hes7 transcriptional repressor may be a direct target of Fgf4 signaling. During vertebrate development, the presomitic mesoderm (PSM) is periodically segmented into somites, which will form the segmented vertebral column and associated muscle, connective tissue, and dermis. The periodicity of somitogenesis is regulated by a segmentation clock of oscillating Notch activity. We examined mouse mutants lacking only Fgf4 or Fgf8, which we previously demonstrated act redundantly to prevent PSM differentiation. Fgf8 is not required for somitogenesis, but Fgf4 mutants display a range of vertebral defects. Analyzing gene expression with spatial model-based quantification of mRNAs fluorescently labeled by hybridization chain reaction, we show that FGF4 controls Notch pathway oscillations through the transcriptional repressor, HES7. We support this hypothesis by demonstrating a genetic synergy between Hes7 and Fgf4, but not with Fgf8. Thus, we establish Fgf4 as an essential Notch oscillation regulator and potentially important in a spectrum of human Segmentation Defects of the Vertebrae caused by defective Notch oscillations. (eLife 2020 Nov 19;9:e55608. doi: 10.7554/eLife.55608.) Future work will focus on what regulatory elements within the Hes7 gene are responsive to Fgf4 signals.