Berking Stefan
Zoological Institute, University of Cologne, Koln, Germany.
Int J Dev Biol. 2006;50(2-3):123-34. doi: 10.1387/ijdb.052043sb.
The freshwater polyp Hydra produces buds which separate from the parent. Other Hydrozoa produce branches which remain connected to the parent, thus forming a colony. Some Hydrozoa grow by means of an organ that is like a shoot apical meristem. Others display a sympodial type of growth. In this article, I propose that these different types of branches are organized by a common pattern-forming system. This system has self-organizing properties. It causes branch tip formation and is kept active in the tip when the tip finally differentiates into a hypostome of a polyp. The system does not cause structure formation directly but rather, determines a tissue property called positional value, in such a way that a gradient of values forms in the tissue of the bud or branch. The local value determines the local morphodynamic processes, including differentiation of the hypostome (highest positional value), tentacles and basal disc and of the exoskeleton pattern along the shoot. A high positional value favors the onset of a new self-organizing process and by lateral inhibition, such a process prevents the initiation of a further process in its surroundings. Small quantitative differences in the range of the signals involved determine whether a bud or a branch forms and whether monopodial and sympodial growth follows.
淡水水螅会产生与母体分离的芽体。其他水螅虫纲动物则产生与母体相连的分支，从而形成群体。一些水螅虫纲动物通过一种类似于茎尖分生组织的器官生长。另一些则呈现出合轴分枝式生长。在本文中，我提出这些不同类型的分支是由一个共同的模式形成系统组织起来的。这个系统具有自组织特性。它导致分支顶端的形成，并在顶端最终分化为水螅的口盘时在顶端保持活跃。该系统并不直接导致结构形成，而是以这样一种方式确定一种称为位置值的组织特性，即在芽体或分支的组织中形成一个值的梯度。局部值决定局部形态动力学过程，包括口盘（最高位置值）、触手、基盘以及沿茎的外骨骼模式的分化。高位置值有利于新的自组织过程的开始，并且通过侧向抑制，这样一个过程会阻止其周围进一步过程的启动。所涉及信号范围的微小数量差异决定了形成的是芽体还是分支，以及是否遵循单轴生长和合轴生长。
