Newman S A
Department of Cell Biology and Anatomy, New York Medical College, Valhalla 10595.
Bioessays. 1993 Apr;15(4):277-83. doi: 10.1002/bies.950150409.
When two populations of cells within a tissue mass differ from one another in magnitude or type of intercellular adhesions, a boundary can form within the tissue, across which cells will fail to mix. This phenomenon may occur regardless of the identity of the molecules that mediate cell adhesion. If, in addition, a choice between the two adhesive states is regulated by a molecule the concentration of which is periodic in space, or in time, then alternating bands of non-mixing tissue, or segments, can form. But temporal or spatial periodicities in concentration will tend to arise for any molecule that is positively autoregulatory. It is therefore proposed that segmentation is a 'generic' property of metazoan organisms, and that metamerism would be expected to have emerged numerous times during evolution. A simple model of segmentation, based solely on differential adhesion and periodic regulation of adhesion, can account for segment properties as disparate as those seen in long and short germ band insects, and for diverse experimental results on boundary regeneration in the chick hind brain and the insect cuticle. It is suggested that the complex, multicomponent segment-forming systems found in contemporary organisms (e.g., Drosophila) are the products of evolutionary recruitment of molecular cues such as homeobox gene products, that increase the reliability and stability of metameric patterns originally templated by generic self-organizing properties of tissues.
当组织团块中的两类细胞群在细胞间黏附的程度或类型上彼此不同时，组织内可形成一个边界，细胞无法跨越该边界混合。无论介导细胞黏附的分子的特性如何，这种现象都可能发生。此外，如果两种黏附状态之间的选择受一种分子调控，且该分子的浓度在空间或时间上呈周期性变化，那么就会形成不混合组织的交替带或节段。但是，对于任何具有正向自我调节作用的分子，其浓度往往会出现时间或空间上的周期性变化。因此有人提出，分节是后生动物的一种“普遍”特性，并且预计在进化过程中同律分节会多次出现。一个仅基于差异黏附和黏附的周期性调节的简单分节模型，能够解释在长胚带和短胚带昆虫中观察到的截然不同的节段特性，以及关于鸡后脑和昆虫表皮边界再生的各种实验结果。有人认为，当代生物体（如果蝇）中发现的复杂的多组分节段形成系统，是分子信号（如同源异型框基因产物）进化招募的产物，这些分子信号提高了最初由组织的一般自组织特性形成的同律模式的可靠性和稳定性。
