Meinhardt Hans
Max-Planck-Institut für Entwicklungsbiologie, Tübingen, Germany.
Int J Dev Biol. 2012;56(6-8):447-62. doi: 10.1387/ijdb.113483hm.
Modeling of pattern formation in hydra has revealed basic mechanisms that underlie the reproducible generation of complex and self-regulating patterns. Organizing regions can be generated by a local self-enhancing reaction that is coupled with an inhibitory effect of longer range. Such reactions enable pattern formation even in an initially almost homogeneous assembly of cells. A long-ranging feedback of the organizer onto the competence to perform the pattern-forming reaction stabilizes the polar axial pattern during growth and allows for regeneration with preserved polarity. Hypostome formation is assumed to be under the control of two positive feedback loops in which Wnt3 is a common element. In addition to the well-established loop employing beta-catenin, a second cell-local loop is involved, possibly with Brachyury as an additional component. This model accounts for the different expression patterns of beta-catenin and Wnt3. Wnt molecules are proposed to play a dual role, functioning as activators and, after processing, as inhibitors. Since Wnt genes code for complete pattern-forming systems, gene duplication and diversification lead to a family of genes whose expression regions have a precise relation to each other. Tentacle formation is an example of positioning a second pattern-forming system by medium-ranging activation and local exclusion exerted by the primary system. A model for bud formation suggests that a transient pre-bud signal is involved that initiates the formation of the foot of the bud, close to the normal foot, as well as close to the bud tip. Many dynamic regulations, as observed in classical and molecular observations, are reproduced in computer simulations. A case is made that hydra can be regarded as a living fossil, documenting an evolutionary early axis formation before trunk formation and bilaterality were invented. Animated simulations are available in the supplementary information accompanying this paper.
水螅中模式形成的建模揭示了复杂且自我调节模式可重复生成的基本机制。组织区域可由局部自我增强反应产生，该反应与更远程的抑制作用相关联。这种反应即使在最初几乎均匀的细胞集合中也能实现模式形成。组织者对进行模式形成反应的能力的长程反馈在生长过程中稳定了极轴模式，并允许在保留极性的情况下进行再生。口盘的形成被认为受两个正反馈回路的控制，其中Wnt3是一个共同元素。除了已确立的使用β-连环蛋白的回路外，还涉及第二个细胞局部回路，可能以短尾相关蛋白作为额外成分。该模型解释了β-连环蛋白和Wnt3的不同表达模式。Wnt分子被认为发挥双重作用，既作为激活剂，经过加工后又作为抑制剂。由于Wnt基因编码完整的模式形成系统，基因复制和多样化导致了一个基因家族，其表达区域彼此具有精确的关系。触手的形成是通过初级系统施加的中程激活和局部排斥来定位第二个模式形成系统的一个例子。一个芽形成的模型表明，涉及一个短暂的芽前信号，该信号启动芽足的形成，靠近正常足部以及靠近芽尖。正如在经典和分子观察中所看到的许多动态调节，在计算机模拟中得到了重现。有人认为水螅可被视为一种活化石，记录了在躯干形成和两侧对称出现之前的进化早期轴的形成。本文的补充信息中有动画模拟。
