Role of BMP and FGF signaling during limb development

与所有三维对象一样，肢体由三个轴组成。这项工作的长期目标是了解形成小鼠胚胎发育肢体的这三个轴的各种信号和遗传路径的相互作用。这不仅将告诉我们肢体在子宫中是如何形成的，还将告诉我们在发育中的胚胎中的其他正常情况下，以及在癌症和先天性疾病等异常情况下，某些信号/遗传途径是如何相互作用的。发育中的肢体是此类研究的理想之选，因为丰富的遗传学和实验胚胎学数据为放置新数据提供了丰富的背景。此前，我们通过研究缺乏编码成纤维细胞生长因子配体的基因的小鼠，展示了成纤维细胞生长因子成纤维细胞生长因子信号在肢体发育过程中的重要作用(Lewis等人。2000自然遗传学28：167，Sun等人2000自然遗传学25：6)。然而，由成纤维细胞生长因子基因冗余引起的复杂性使我们考虑通过检测成纤维细胞生长因子受体突变来解决这一问题，从而得出成纤维细胞生长因子信号控制肢体大小的见解(Verheyden JM等人，2005Development 132：4235)。我们也在研究成纤维细胞生长因子和骨形态发生蛋白信号的相互关系。目前的肢体发育模型表明，BMP信号在控制指间充质细胞的正常细胞死亡中发挥作用，塑造最终的手指模式，但BMP在这一过程中的确切作用尚不清楚。通过在肢芽外胚层中同时失活BMP受体基因BMPR1a以及Fgf8和Fgf4，我们已经为一种新的模型提供了遗传学证据，在该模型中，表面外胚层必须接收BMP信号，导致FGFs下调，进而诱导潜在的间充质细胞凋亡。因此，骨形态发生蛋白和成纤维细胞生长因子共同控制细胞程序性死亡的基本功能。我们正在通过研究BMP和FGF信号在肢体发育的各个方面的作用来扩展这些研究，使用在发育肢体的特定区域表达Cre的小鼠系。例如，检验BMPs作为细胞死亡直接效应因子的假设的唯一方法是，仅在经历细胞死亡的谱系中使BMPs受体失活，而不影响附近细胞中的基因。我们已经使用新的Cre品系实现了这一点，这种品系允许Cre介导的基因在这些谱系中失活。这些问题是：BMP是正常的程序性细胞死亡的直接影响因素吗？如果不是，程序性细胞死亡是如何控制的？如果是这样，BMP是如何实现这一目标的？

Like all three-dimensional objects, the limb consists of three axes. The long-term goal of this work is to understand the interactions of various signaling and genetic pathways that pattern these three axes of the developing limb of the mouse embryo. This will not only tell us how a limb forms in utero, but will tell us how certain signaling/genetic pathways interact with each other in other normal contexts in the developing embryo as well as in abnormal contexts such as cancer and congenital disease. The developing limb is ideal for such studies because a wealth of genetic and experimental embryological data provides a rich context in which to place new data. Previously we have shown an essential role for fibroblast growth factor FGF signaling during limb development by examining mice lacking genes that encode FGF ligands (Lewandoski et al. 2000 Nature Genetics 28:167, Sun et al 2000 Nature Genetics 25: 6 ). However, the complexity caused by Fgf gene redundancy has led us to consider approaching the problem by examining FGF receptor mutants leading to the insight that FGF signaling controls limb size (Verheyden JM et al 2005Development 132:4235). We are also studying the inter-relationship between FGF and BMP signaling. Current models of limb development suggest that BMP signaling plays a role in controlling the normal cell death that occurs in mesenchymal interdigit cells, sculpting the final digit pattern, but the exact role of BMPs in this process are unknown. By simultaneously inactivating the Bmp receptor gene, Bmpr1a as well as Fgf8 and Fgf4 specifically in the limb bud ectoderm, we have produced genetic evidence for a novel model in which the surface ectoderm must receive a BMP signal, resulting in down regulation of Fgfs which in turn induces apoptosis of the underlying mesenchyme. Thus both BMPs and FGF cooperate to control the essential cell function of programmed cell death. We are extending these studies by studying the role of BMP and FGF signaling in various aspects of limb development using mouse lines that express Cre in specific region of the developing limb. For example the only way to test the hypothesis that BMPs act as direct effectors of cell death is to inactivate BMPs receptors only in the lineage that undergoes cells death, without affect genes in nearby cells. We have achieved this using new Cre lines which allow Cre-mediated gene inactivation in these lineages. With these lines are asking: are BMPs are direct effectors of normal programmed cell death? If not, how is programmed cell death controlled? If so, how do BMPs achieve this endpont?