Bar I, Goffinet A M
Neurobiology Unit, University of Namur Medical School, Belgium.
Novartis Found Symp. 2000;228:114-25; discussion 125-8. doi: 10.1002/0470846631.ch9.
The mammalian cortical plate is characterized by its radial organization and its inside-outside developmental gradient. Observations on reelin and Dab1-deficient mice show that reelin and Dab1 are both required to develop radial cortical organization and a normal maturation gradient. In the reptilian cortex, radial organization varies among species; it is the most rudimentary in turtles and the most elaborate in lizards, and can be described as intermediate in other species such as crocodilians and Sphenodon. On the other hand, the gradient of corticogenesis is directed from outside to inside in all reptiles studied, as well as in mice that are deficient in reelin, Dab1, as well as cyclin-dependent kinase 5 (Cdk5) and p35. All reptiles, even turtles, have reelin-expressing cells in the embryonic marginal zone. Mammals are characterized by a drastic increase in the number of reelin-positive cells (Cajal-Retzius cells) as well as by an amplification of reelin expression per cell. In lizards, the pattern of reelin expression is different, as reelin-expressing cells are also present below the cortical plate. In all mammalian and reptilian species, Dab1 is expressed in cortical plate cells. These data suggest that the reelin/Dab1 pathway was a driver of cortical evolution on the synapsid lineage and that similarities in radial cortical organization between squamates and mammals result from evolutionary convergence.
哺乳动物的皮质板以其放射状组织和由内向外的发育梯度为特征。对缺乏reelin和Dab1的小鼠的观察表明，reelin和Dab1都是发育放射状皮质组织和正常成熟梯度所必需的。在爬行动物的皮质中，放射状组织在不同物种之间有所不同；在龟类中最为原始，在蜥蜴中最为复杂，在其他物种如鳄鱼和楔齿蜥中可描述为中等程度。另一方面，在所有研究的爬行动物以及缺乏reelin、Dab1以及细胞周期蛋白依赖性激酶5（Cdk5）和p35的小鼠中，皮质发生的梯度都是由外向内的。所有爬行动物，甚至龟类，在胚胎边缘区都有表达reelin的细胞。哺乳动物的特征是reelin阳性细胞（Cajal-Retzius细胞）数量急剧增加，以及每个细胞中reelin表达的扩增。在蜥蜴中，reelin的表达模式不同，因为表达reelin的细胞也存在于皮质板下方。在所有哺乳动物和爬行动物物种中，Dab1都在皮质板细胞中表达。这些数据表明，reelin/Dab1通路是突触谱系上皮质进化的驱动力，并且有鳞目动物和哺乳动物之间放射状皮质组织的相似性是进化趋同的结果。
