Specialized filopodia direct long-range transport of SHH during vertebrate tissue patterning.
Specialized filopodia direct long-range transport of SHH during vertebrate tissue patterning.
复制标题
作者：
信号蛋白穿越含有紧密堆积细胞的组织的能力对细胞规范和组织发育至关重要，然而，如何在细胞水平上实现这一目标仍然知之甚少。一个多世纪以来，脊椎动物肢体芽一直是研究胚胎发育过程中细胞信号传导的范例。在这里，我们优化了单细胞实时成像，以描绘具有膜结合共价脂质修饰的信号蛋白（如Sonic Hedgehog (Shh)）如何在体内肢体芽内长距离传播的细胞机制。通过直接成像Shh配体在天然调节控制下的产生，我们的研究结果表明，Shh意外地以一种颗粒的形式产生，这种颗粒通过跨越几个细胞直径的长细胞质延伸与细胞保持联系。我们发现这些细胞延伸是一类特殊的基于肌动蛋白的丝状足，具有新的细胞骨架特征，以前没有描述过。引人注目的是，含有Shh的颗粒沿着这些延伸在Shh细胞信号传导范围内进行净顺行运动。我们进一步表明，在Shh应答细胞中，Shh共受体的特定亚群，包括Cdo和Boc，在远离细胞体的丝状延伸的特定微域内积极分布和共定位。在含有Shh配体的丝状足和含有共受体的丝状足之间形成稳定的远距离相互作用。这些结果表明，由特殊丝状足传播的接触介导释放有助于Shh在远处的传递。总之，这些研究确定了一种重要的细胞间通讯模式，显著扩展了我们对脊椎动物组织模式过程中配体运动和接受的理解。
The ability of signaling proteins to traverse tissues containing tightly packed cells is of fundamental importance for cell specification and tissue development, however, how this is achieved at a cellular level remains poorly understood. For over a century, the vertebrate limb bud has served as a paradigm to study cell signaling during embryonic development. Here we optimize single cell real-time imaging to delineate the cellular mechanisms for how signaling proteins, such as Sonic Hedgehog (Shh), that possess membrane-bound covalent lipid modifications transverse long distances within the limb bud in vivo. By directly imaging Shh ligand production under native regulatory control, our findings show that Shh is unexpectedly produced in the form of a particle that remains associated with the cell via long cytoplasmic extensions that span several cell diameters. We show that these cellular extensions are a specialized class of actin-based filopodia with novel cytoskeletal features that have not been previously described. Strikingly, particles containing Shh traffic along these extensions with a net anterograde movement within the field of Shh cell signaling. We further show that in Shh responding cells specific subsets of Shh co-receptors, including Cdo and Boc, actively distribute and co-localize in specific micro-domains within filopodial extensions, far from the cell body. Stabilized interactions are formed between filopodia containing Shh ligand and those containing co-receptors over a long-range. These results suggest that contact-mediated release propagated by specialized filopodia contributes to the delivery of Shh at a distance. Together, these studies identify an important mode of communication between cells that significantly extends our understanding of ligand movement and reception during vertebrate tissue patterning.