Life and Health Sciences Research Institute (ICVS), School of Health Sciences, University of Minho , 4710-057 Braga , Portugal; ICVS/3B's - PT Government Associate Laboratory, Braga/Guimarães, Portugal ; Regenerative Medicine Program, Departamento de Ciências Biomédicas e Medicina, Universidade do Algarve , 8005-139 Faro , Portugal; IBB-Institute for Biotechnology and Bioengineering, Centro de Biomedicina Molecular e Estrutural, Universidade do Algarve, 8005-139 Faro, Portugal.
Biol Open. 2012 Nov 15;1(11):1102-10. doi: 10.1242/bio.20122386. Epub 2012 Aug 21.
Embryo development requires precise orchestration of cell proliferation and differentiation in both time and space. A molecular clock operating through gene expression oscillations was first described in the presomitic mesoderm (PSM) underlying periodic somite formation. Cycles of HES gene expression have been further identified in other progenitor cells, including the chick distal limb mesenchyme, embryonic neural progenitors and both mesenchymal and embryonic stem cells. In the limb, hairy2 is expressed in the distal mesenchyme, adjacent to the FGF source (AER) and along the ZPA-derived SHH gradient, the two major regulators of limb development. Here we report that hairy2 expression depends on joint AER/FGF and ZPA/SHH signaling. FGF plays an instructive role on hairy2, mediated by Erk and Akt pathway activation, while SHH acts by creating a permissive state defined by Gli3-A/Gli3-R>1. Moreover, we show that AER/FGF and ZPA/SHH present distinct temporal and spatial signaling properties in the distal limb mesenchyme: SHH acts at a long-term, long-range on hairy2, while FGF has a short-term, short-range action. Our work establishes limb hairy2 expression as an output of integrated FGF and SHH signaling in time and space, providing novel clues for understanding the regulatory mechanisms underlying HES oscillations in multiple systems, including embryonic stem cell pluripotency.
胚胎发育需要在时间和空间上精确协调细胞增殖和分化。最初在周期性体节形成的脊椎前中胚层（PSM）中描述了通过基因表达振荡运行的分子钟。HES 基因表达的周期在其他祖细胞中进一步被鉴定出来，包括鸡的远端肢体间充质、胚胎神经祖细胞以及间质和胚胎干细胞。在肢体中，Hairy2 在远端间充质中表达，位于 FGF 来源（AER）附近，以及沿 ZPA 衍生的 SHH 梯度，这是肢体发育的两个主要调节剂。在这里，我们报告说 Hairy2 的表达取决于关节 AER/FGF 和 ZPA/SHH 信号。FGF 通过激活 Erk 和 Akt 途径对 Hairy2 发挥指导作用，而 SHH 通过创建由 Gli3-A/Gli3-R>1 定义的许可状态发挥作用。此外，我们表明 AER/FGF 和 ZPA/SHH 在远端肢体间充质中具有不同的时空信号特性：SHH 长期、远程作用于 Hairy2，而 FGF 具有短期、短程作用。我们的工作将肢体 Hairy2 的表达确立为时间和空间上整合的 FGF 和 SHH 信号的输出，为理解包括胚胎干细胞多能性在内的多个系统中 HES 振荡的调节机制提供了新的线索。
