Shimogori Tomomi, Grove Elizabeth A
Department of Neurobiology, Pharmacology, and Physiology, University of Chicago, Chicago, Illinois 60637, USA.
J Neurosci. 2005 Jul 13;25(28):6550-60. doi: 10.1523/JNEUROSCI.0453-05.2005.
Thalamic innervation of each neocortical area is vital to cortical function, but the developmental strategies that guide axons to specific areas remain unclear. We took a new approach to determine the contribution of intracortical cues. The cortical patterning molecule fibroblast growth factor 8 (FGF8) was misexpressed in the cortical primordium to rearrange the area map. Thalamic axons faithfully tracked changes in area position and innervated duplicated somatosensory barrel fields induced by an ectopic source of FGF8, indicating that thalamic axons indeed use intracortical positional information. Because cortical layers are generated in temporal order, FGF8 misexpression at different ages could be used to shift regional identity in the subplate and cortical plate either in or out of register. Thalamic axons showed strikingly different responses in the two different conditions, disclosing sources of positional guidance in both subplate and cortical plate. Unexpectedly, axon trajectories indicated that an individual neocortical layer could provide not only laminar but also area-specific guidance. Our findings demonstrate that thalamocortical axons are directed by sequential, positional cues within the cortex and implicate FGF8 as an indirect regulator of thalamocortical innervation.
丘脑对每个新皮质区域的神经支配对皮质功能至关重要，但引导轴突到达特定区域的发育策略仍不清楚。我们采用了一种新方法来确定皮质内线索的作用。在皮质原基中错误表达皮质模式分子成纤维细胞生长因子8（FGF8），以重新排列区域图谱。丘脑轴突忠实地追踪区域位置的变化，并支配由异位FGF8来源诱导产生的重复的体感桶状区，这表明丘脑轴突确实利用了皮质内的位置信息。由于皮质层是按时间顺序生成的，在不同年龄错误表达FGF8可用于使板下层和皮质板中的区域身份发生移位，无论是对齐还是不对齐。丘脑轴突在两种不同情况下表现出截然不同的反应，揭示了板下层和皮质板中位置引导的来源。出乎意料的是，轴突轨迹表明，单个新皮质层不仅可以提供层特异性引导，还可以提供区域特异性引导。我们的研究结果表明，丘脑皮质轴突由皮质内的顺序性位置线索引导，并表明FGF8是丘脑皮质神经支配的间接调节因子。
