Molecular control of smooth muscle cell differentiation in the developing murine ureter

输尿管收缩活动的结构基础是平滑肌细胞（SMC）和纤维弹性材料的外部间充质投资。这些分化的细胞类型通过多步发育程序从间充质前体细胞的未分化池中产生。虽然输尿管壁的先天性异常是常见的，并可能对肾功能产生有害的后果，但对输尿管间质中SMCs分化的分子电路知之甚少。在第一个资助期，我们通过小鼠的遗传分析表明，Hedgehog（HH）信号传导是胚胎输尿管内间充质细胞层增殖和SMC分化所必需的。这些SHH信号传导功能完全由Forkhead转录因子FOXF 1介导。FOXF 1激活Bmp 4的表达，并在这些细胞程序的进一步执行中与该间充质信号的AKT和SMAD效应子通路合作。我们确定了SRF/GATA 6、FGFR 2和PDGFRA作为对SMC分化有积极影响的额外因子，而视黄酸信号传导被表征为维持间充质前体库并抑制SMC分化的途径。在第二个资助期，我们希望结合基因靶向研究、输尿管外植体培养物的药理学操作以及小规模和大规模分子测定，以更深入地了解发育中输尿管中SMC特异性基因表达的分子激活。我们希望描绘发育中的输尿管间充质的转录景观，并确定SRF/MYOCD转录调节因子对SMC特异性转录组的激活的影响。我们希望进一步确定SMC程序中关键信号通路的分子功能。对于SHH-FOXF 1-BMP 4模块，我们希望表征Foxf 1表达的分子调控，并鉴定和功能性表征FOXF 1和SMAD 1/5/9-SMAD 4转录激活因子的直接靶点。我们希望确定RA和BMP 4信号在维持输尿管间充质祖细胞状态中的分子结果，并研究FGFR 2和PDGFRA信号在该组织中的细胞和分子功能。最后，我们想研究这些信号通路是如何改变其活性，以抑制SMC和有利于固有层形成在输尿管发育的后期阶段。我们期望从这些研究中获得控制内脏器官SMC分化的分子机制的新见解，以及先天性梗阻性肾病的病因学。

Structural basis of the contractile activity of the ureter is an outer mesenchymal investment of smooth muscle cells (SMCs) and fibroelastic material. These differentiated cell types arise through a multi-step developmental program from an undifferentiated pool of mesenchymal precursor cells. Although congenital anomalies of the ureteric wall are frequent and may have deleterious consequences for renal function, little is known about the molecular circuits that orchestrate the differentiation of SMCs in the ureteric mesenchyme. In the first funding period we showed by genetic analyses in the mouse, that Hedgehog (HH) signaling is required for proliferation and SMC differentiation of the inner mesenchymal cell layer in the embryonic ureter. These SHH signaling functions are completely mediated by the Forkhead transcription factor FOXF1. FOXF1 activates Bmp4 expression and cooperates with the AKT and SMAD effector pathways of this mesenchymal signal in the further execution of these cellular programs. We identified SRF/GATA6, FGFR2 and PDGFRA as additional factors that positively impact on SMC differentiation whereas retinoic acid signaling was characterized as a pathway that maintains the mesenchymal precursor pool and inhibits SMC differentiation. In the second funding period we want to use a combination of gene targeting studies, pharmacological manipulation of ureter explant cultures, and small and large scale molecular assays to get a deeper understanding about the molecular activation of SMC specific gene expression in the developing ureter. We wish to profile the transcriptional landscape of the developing ureteric mesenchyme, and determine the impact which the SRF/MYOCD transcriptional regulator has on the activation of the SMC specific transcriptome. We wish to further define the molecular function of key signaling pathways in the SMC program. For the SHH-FOXF1-BMP4 module, we want to characterize the molecular regulation of Foxf1 expression, and identify and functionally characterize the direct targets of FOXF1 and SMAD1/5/9-SMAD4 transcriptional activators. We want to determine the molecular consequences of combined RA and BMP4 signaling in maintaining the progenitor state of the ureteric mesenchyme, and investigate the cellular and molecular functions of FGFR2 and PDGFRA signaling in this tissue. Finally, we want to investigate how these signaling pathways are altered in their activity to suppress SMC and favor Lamina propria formation at later stages of ureter development. We expect from these studies new insights in the molecular mechanisms that control SMC differentiation of visceral organs, and into the etiology of congenital obstructive nephropathy.