Sestan N, Rakic P, Donoghue M J
Section of Neurobiology, Yale University School of Medicine, New Haven, CT 06510, USA.
Curr Biol. 2001 Jan 9;11(1):39-43. doi: 10.1016/s0960-9822(00)00043-9.
The visual cortex in primates is parcellated into cytoarchitectonically, physiologically, and connectionally distinct areas: the striate cortex (V1) and the extrastriate cortex, consisting of V2 and numerous higher association areas [1]. The innervation of distinct visual cortical areas by the thalamus is especially segregated in primates, such that the lateral geniculate (LG) nucleus specifically innervates striate cortex, whereas pulvinar projections are confined to extrastriate cortex [2--8]. The molecular bases for the parcellation of the visual cortex and thalamus, as well as the establishment of reciprocal connections between distinct compartments within these two structures, are largely unknown. Here, we show that prospective visual cortical areas and corresponding thalamic nuclei in the embryonic rhesus monkey (Macaca mulatta) can be defined by combinatorial expression of genes encoding Eph receptor tyrosine kinases and their ligands, the ephrins, prior to obvious cytoarchitectonic differentiation within the cortical plate and before the establishment of reciprocal connections between the cortical plate and thalamus. These results indicate that molecular patterns of presumptive visual compartments in both the cortex and thalamus can form independently of one another and suggest a role for EphA family members in both compartment formation and axon guidance within the visual thalamocortical system.
灵长类动物的视觉皮层被划分为细胞结构、生理和连接上不同的区域：纹状皮层（V1）和纹外皮层，后者由V2和众多高级联合区域组成[1]。在灵长类动物中，丘脑对不同视觉皮层区域的神经支配特别分离，使得外侧膝状（LG）核专门支配纹状皮层，而丘脑枕投射则局限于纹外皮层[2 - 8]。视觉皮层和丘脑划分的分子基础，以及这两个结构内不同区域之间相互连接的建立，在很大程度上尚不清楚。在这里，我们表明，在胚胎恒河猴（猕猴）的皮层板内明显的细胞结构分化之前以及皮层板与丘脑之间建立相互连接之前，编码Eph受体酪氨酸激酶及其配体（ephrins）的基因的组合表达可以定义预期的视觉皮层区域和相应的丘脑核。这些结果表明，皮层和丘脑中假定的视觉区域的分子模式可以彼此独立形成，并提示EphA家族成员在视觉丘脑皮层系统内的区域形成和轴突导向中发挥作用。
