The Role of Fgf Signaling in Vertebrate Development

该项目的长期目标是了解一个重要的信号配体家族，称为成纤维细胞生长因子（FGFs），如何控制广泛的细胞生物学行为，如增殖，细胞死亡，迁移，干细胞维持和基因表达。特别是，我们使用复杂的小鼠遗传学来理解FGF信号在中胚层谱系中的作用，特别强调体轴的延伸和体节的形成（分割的中胚层节段是脊椎动物肌肉、真皮和椎体的基石）。我们的工作已经清楚地表明，基因冗余是这种生物学的一个重要方面；因此，本项目的所有工作都是为了全面表征中胚层谱系中FGF信号的遗传冗余。这项工作与许多可能有一个以上FGF基因受损的癌症病例有关。为了实现这一目标，我们已经产生并表征了重要的Cre小鼠系，这是允许控制早期胚胎基因表达的工具。这些基因包括tcree（表达于早期新生中胚层）、TCreERT2（可在所有胚胎阶段的新生中胚层活化）和Tbx4-Cre（表达于后胚层区域，包括尿囊、后肢和外生殖器）。特别是tcr对该领域产生了重大影响，在20多份出版物中发挥了重要作用。除了为小鼠遗传学社区提供有价值的小鼠品系外，该项目还发表了一些论文，记录了我们对早期胚胎中FGF信号传导的主要见解。我们发表了Fgf8不是体细胞发生所必需的，尽管在当前的模型中，大量的高知名度的工作已经把它放在了中心位置。然而，通过与Alan Perantoni的合作，我们证明了Fgf8对肾脏和男性生殖道的发育至关重要。我们发现Fgf8和Fgf4在体细胞发生的一些基本方面是必需的：振荡基因结构域、WNT通路基因和未分化的体细胞前中胚层的标记物的表达。重要的是，我们证明了整个体前中胚层的过早分化。通过研究类似的突变体，我们从基因上恢复了WNT信号，我们证明了FGF信号在这一过程中独立于WNT信号。我们发现的这种功能冗余对癌症有影响，因为两种fgf在睾丸肿瘤中都异常活跃。此外，这种冗余对进化有影响，因为相同的FGFs在肢体发育中起补偿作用。我们正在继续研究胚胎发育过程中FGF信号的遗传冗余。例如，我们正在研究Fgf3在胚胎轴终止中的作用。我们正在研究Fgf4和Fgf8在体细胞分化为其衍生谱系（肌肉和骨）中的作用。在这个项目的另一部分，我们正在研究这些Fgfs在尿囊发育中的作用，尿囊是胎盘血管和脐带的组织。在人类中，这种组织不能正常发育是导致妊娠流产的许多原因。

The long term goal of this project is to understand how a the important family of signaling ligands, called Fibroblast Growth Factors (FGFs), control a wide spectrum of cell biological behaviors such as proliferation, cell death, migration, stem cell maintenance and gene expression. In particular we use complex mouse genetics to understand the role of FGF signaling in mesodermal lineages with a special emphasis on extension of the body axis and formation of somites (segmented mesodermal segments that are the building blocks of vertebrate muscle, dermis and vertebral bodies). Our work has made clear that genetic redundancy is an important aspect of this biology; therefore all work in this project emerges from an effort to comprehensively characterize the genetic redundancy of FGF signaling in the mesodermal lineage. Such work is relevant to many cases of cancer where more than one FGF gene may be damaged. To achieve this, we have generated and characterized important Cre mouse lines, which are tools that allow the control of gene expression in the early embryo. These include TCre (expressed in the early emerging nascent mesoderm), TCreERT2 (activatable in emerging nascent mesoderm at all embryonic stages) and Tbx4-Cre (expressed in a posterior mesodermal domain that includes the allantois, hindlimb, and external genitalia. TCre in particular has had a major impact on the field, being essential in over 20 publications.Besides providing the mouse genetics community with valuable mouse lines, this project has yielded papers that document our major insights regarding FGF signaling in the early embryo. We published that Fgf8 not required for somitogenesis, although a body of high profile work had placed it in a central position in current models. However, in collaboration with Alan Perantoni, we demonstrated that Fgf8 was essential for development of the kidney and male reproductive tract.We showed that Fgf8, together with Fgf4, are required for essential aspects of somitogenesis: expression of oscillating gene domains, WNT pathway genes and markers of undifferentiated presomitic mesoderm. Importantly, we demonstrated the premature differentiation of the entire presomitic mesoderm. By examining similar mutants in which we genetically restored WNT signaling, we demonstrated that FGF signaling operates independently of WNT signaling in this process. This functional redundancy that we uncovered has implications for cancer as both FGFs have been found to be aberrantly active in testicular tumors. Furthermore this redundancy has implications for evolution as the same FGFs play compensatory roles in limb development. We are continuing to study genetic redundancy in FGF signaling in several aspects of embryonic development. For example, we are investigating the role of Fgf3 in termination of the embryonic axis. We are investigating the role of Fgf4 and Fgf8 in the differentiation of the somite into its derivative lineages (muscle and bone). In another part of this project, we are studying the role of these Fgfs in development of the allantois, a tissue that gives rise to the placental blood vessels and the umbilical cord. In human, failure of this tissue to develop properly underlies many aspects of pregnancy loss.