Miyagawa Shinichi, Moon Anne, Haraguchi Ryuma, Inoue Chie, Harada Masayo, Nakahara Chiaki, Suzuki Kentaro, Matsumaru Daisuke, Kaneko Takehito, Matsuo Isao, Yang Lei, Taketo Makoto M, Iguchi Taisen, Evans Sylvia M, Yamada Gen
Institute of Molecular Embryology and Genetics, Global COE 'Cell Fate Regulation Research and Education Unit', Kumamoto University, Kumamoto 860-0811, Japan.
Development. 2009 Dec;136(23):3969-78. doi: 10.1242/dev.039438.
Embryonic appendicular structures, such as the limb buds and the developing external genitalia, are suitable models with which to analyze the reciprocal interactions of growth factors in the regulation of outgrowth. Although several studies have evaluated the individual functions of different growth factors in appendicular growth, the coordinated function and integration of input from multiple signaling cascades is poorly understood. We demonstrate that a novel signaling cascade governs formation of the embryonic external genitalia [genital tubercle (GT)]. We show that the dosage of Shh signal is tightly associated with subsequent levels of Wnt/beta-catenin activity and the extent of external genitalia outgrowth. In Shh-null mouse embryos, both expression of Wnt ligands and Wnt/beta-catenin signaling activity are downregulated. beta-catenin gain-of-function mutation rescues defective GT outgrowth and Fgf8 expression in Shh-null embryos. These data indicate that Wnt/beta-catenin signaling in the distal urethral epithelium acts downstream of Shh signaling during GT outgrowth. The current data also suggest that Wnt/beta-catenin regulates Fgf8 expression via Lef/Tcf binding sites in a 3' conserved enhancer. Fgf8 induces phosphorylation of Erk1/2 and cell proliferation in the GT mesenchyme in vitro, yet Fgf4/8 compound-mutant phenotypes indicate dispensable functions of Fgf4/8 and the possibility of redundancy among multiple Fgfs in GT development. Our results provide new insights into the integration of growth factor signaling in the appendicular developmental programs that regulate external genitalia development.
胚胎附属结构，如肢芽和发育中的外生殖器，是分析生长因子在生长调节中相互作用的合适模型。尽管有几项研究评估了不同生长因子在附属生长中的个体功能，但对多个信号级联输入的协同功能和整合了解甚少。我们证明了一种新的信号级联控制胚胎外生殖器[生殖结节（GT）]的形成。我们表明，Shh信号的剂量与随后的Wnt/β-连环蛋白活性水平和外生殖器生长程度密切相关。在Shh基因缺失的小鼠胚胎中，Wnt配体的表达和Wnt/β-连环蛋白信号活性均下调。β-连环蛋白功能获得性突变挽救了Shh基因缺失胚胎中GT生长缺陷和Fgf8表达。这些数据表明，在GT生长过程中，远端尿道上皮中的Wnt/β-连环蛋白信号在Shh信号下游起作用。目前的数据还表明，Wnt/β-连环蛋白通过3'保守增强子中的Lef/Tcf结合位点调节Fgf8表达。Fgf8在体外诱导GT间充质中Erk1/2的磷酸化和细胞增殖，但Fgf4/8复合突变体表型表明Fgf4/8在GT发育中功能可有可无，且多种Fgf之间可能存在冗余。我们的结果为调节外生殖器发育的附属发育程序中生长因子信号的整合提供了新的见解。
