Kcnab1 Is Expressed in Subplate Neurons With Unilateral Long-Range Inter-Areal Projections
Kcnab1 Is Expressed in Subplate Neurons With Unilateral Long-Range Inter-Areal Projections
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DOI：
10.3389/fnana.2019.00039
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发表时间：
2019-05-03
影响因子：
2.9
通讯作者：
Sato, Makoto
中科院分区：
文献类型：
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作者：
Tiong, Sheena Yin Xin;Oka, Yuichiro;Sato, Makoto
亚板（SP）神经元是大脑皮层中最早产生的神经元之一，在基因表达方面具有异质性。SP神经元主要由投射神经元组成，其轴突在发育早期就开始向特定目标区域延伸。然而，轴突投射与SP神经元及其残余层6b （L6b）神经元的基因表达模式之间的关系在很大程度上是未知的。在本研究中，我们分析了小鼠皮层中L6b/SP神经元的皮质-皮质投射，并寻找具有同侧区域间投射的L6b/SP神经元中表达的标记基因。逆行示踪实验表明，初级体感觉皮层（S1）中的L6b/SP神经元在出生后（PD） 2时投射到同一皮质半球的初级运动皮层（M1），但未显示任何胼胝体投射。这种单侧投射模式一直持续到成年。我们的微阵列分析发现编码电压门控钾通道β亚基（Kcnab1）的基因在L6b/SP中表达。双标记逆行示踪和原位杂交表明Kcnab1在L6b/SP的单侧突起神经元中表达。早在胚胎期(E) 14.5，即SP出现后不久，就在SP中特异性检测到胚胎表达。双免疫染色实验显示，蛋白产物Kv β 1与L6b/SP标记物Ctgf（88%）、Cplx3（79%）和Nurr1（58%）共表达不同程度，提示单侧突出的L6b/SP神经元存在分子细分。除了在L6b/SP中表达外，Kcnab1在出生后各阶段均有分散表达，无层特异性。在具有三个备选第一外显子的剪接变体中，变体1.1解释了本研究中提到的所有皮质表达。总之，我们的数据表明L6b/SP神经元具有皮质-皮质投射，Kcnab1的表达定义了L6b/SP神经元的一个亚群，具有单侧区域间投射。
Subplate (SP) neurons are among the earliest-born neurons in the cerebral cortex and heterogeneous in terms of gene expression. SP neurons consist mainly of projection neurons, which begin to extend their axons to specific target areas very early during development. However, the relationships between axon projection and gene expression patterns of the SP neurons, and their remnant layer 6b (L6b) neurons, are largely unknown. In this study, we analyzed the corticocortical projections of L6b/SP neurons in the mouse cortex and searched for a marker gene expressed in L6b/SP neurons that have ipsilateral inter-areal projections. Retrograde tracing experiments demonstrated that L6b/SP neurons in the primary somatosensory cortex (S1) projected to the primary motor cortex (M1) within the same cortical hemisphere at postnatal day (PD) 2 but did not show any callosal projection. This unilateral projection pattern persisted into adulthood. Our microarray analysis identified the gene encoding a beta subunit of voltage-gated potassium channel (Kcnab1) as being expressed in L6b/SP. Double labeling with retrograde tracing and in situ hybridization demonstrated that Kcnab1 was expressed in the unilaterally-projecting neurons in L6b/SP. Embryonic expression was specifically detected in the SP as early as embryonic day (E) 14.5, shortly after the emergence of SP. Double immunostaining experiments revealed different degrees of co-expression of the protein product Kv beta 1 with L6b/SP markers Ctgf (88%), Cplx3 (79%), and Nurr1 (58%), suggesting molecular subdivision of unilaterally-projecting L6b/SP neurons. In addition to expression in L6b/SP, scattered expression of Kcnab1 was observed during postnatal stages without layer specificity. Among splicing variants with three alternative first exons, the variant 1.1 explained all the cortical expression mentioned in this study. Together, our data suggest that L6b/SP neurons have corticocortical projections and Kcnab1 expression defines a subpopulation of L6b/SP neurons with a unilateral interareal projection.