Tissir F, Lambert de Rouvroit C, Goffinet A M
Developmental Genetics Unit, GEDE 7382, University of Louvain Medical School, Brussels, Belgium.
Braz J Med Biol Res. 2002 Dec;35(12):1473-84. doi: 10.1590/s0100-879x2002001200007.
Reelin is an extracellular matrix protein that is defective in reeler mutant mice and plays a key role in the organization of architectonic patterns, particularly in the cerebral cortex. In mammals, a "reelin signal" is activated when reelin, secreted by Cajal-Retzius neurons, binds to receptors of the lipoprotein receptor family on the surface of cortical plate cells, and triggers Dab1 phosphorylation. As reelin is a key component of cortical development in mammals, comparative embryological studies of reelin expression were carried out during cortical development in non-mammalian amniotes (turtles, squamates, birds and crocodiles) in order to assess the putative role of reelin during cortical evolution. The data show that reelin is present in the cortical marginal zone in all amniotes, and suggest that reelin has been implicated in the evolution of the radial organization of the cortical plate in the synapsid lineage leading from stem amniotes to mammals, as well as in the lineage leading to squamates, thus providing an example of homoplastic evolution (evolutionary convergence). The mechanisms by which reelin instructs radial cortical organization in these two lineages seem different: in the synapsid lineage, a drastic amplification of reelin production occurred in Cajal-Retzius cells, whereas in squamates, in addition to reelin-secreting cells in the marginal zone, a second layer of reelin-producing cells developed in the subcortex. Altogether, our results suggest that the reelin-signaling pathway has played a significant role in shaping the evolution of cortical development.
Reelin是一种细胞外基质蛋白，在reeler突变小鼠中存在缺陷，在结构模式的组织中起关键作用，尤其是在大脑皮层。在哺乳动物中，当由Cajal-Retzius神经元分泌的Reelin与皮质板细胞表面脂蛋白受体家族的受体结合并触发Dab1磷酸化时，“Reelin信号”被激活。由于Reelin是哺乳动物皮层发育的关键组成部分，因此在非哺乳动物羊膜动物（龟、有鳞类动物、鸟类和鳄鱼）的皮层发育过程中进行了Reelin表达的比较胚胎学研究，以评估Reelin在皮层进化过程中的假定作用。数据表明，Reelin存在于所有羊膜动物的皮质边缘区，并表明Reelin与从羊膜动物祖先到哺乳动物的合弓纲谱系以及有鳞类动物谱系中皮质板的放射状组织的进化有关，从而提供了一个趋同进化（进化趋同）的例子。Reelin在这两个谱系中指导皮质放射状组织的机制似乎不同：在合弓纲谱系中，Cajal-Retzius细胞中Reelin的产生发生了急剧扩增，而在有鳞类动物中，除了边缘区分泌Reelin的细胞外，皮层下还形成了第二层产生Reelin的细胞。总之，我们的结果表明，Reelin信号通路在塑造皮层发育的进化过程中发挥了重要作用。
