Leingärtner Axel, Richards Linda J, Dyck Richard H, Akazawa Chihiro, O'Leary Dennis D M
Molecular Neurobiology Laboratory, The Salk Institute, 10010 North Torrey Pines Road, La Jolla, CA 92037, USA.
Cereb Cortex. 2003 Jun;13(6):648-60. doi: 10.1093/cercor/13.6.648.
A goal of this study was to use recombinant adenovirus (AdV) to ectopically express Emx2 in the embryonic neocortex as a gain-of-function approach to study its role in the area-specific targeting of thalamocortical axons (TCAs), using the rat as a model. First, we cloned the cDNA for the full-length coding region of rat Emx2, a homologue of Drosophila empty spiracles. We also used this sequence to define the full-length coding region of mouse Emx2 from genomic DNA. Our analysis of Emx2 expression shows that in rat, as reported in mouse, Emx2 is expressed in high caudal to low rostral, and high medial to low lateral, gradients across the cortex throughout cortical neurogenesis, and expression is primarily restricted to progenitors in the neuroepithelium. We also carried out an analysis of the distribution of cells infected with a replication defective recombinant type 5 adenovirus (AdV) containing a CAG/LacZ expression construct, following an injection into the lateral ventricle of the cerebral hemisphere at different stages of embryonic cortical neurogenesis. AdV-infected cells are broadly distributed tangentially, but their laminar distribution is differentially restricted and reflects the temporal sequence of generation of cortical neurons. This finding indicates that the AdV predominantly infects progenitors in the ventricular zone, which leads to a preferential labeling of their immediate progeny, and infects cells that have recently become postmitotic and have yet to move far from the ventricular surface. We then show that AdV-mediated ectopic Emx2 expression results in aberrant intracortical pathfinding and areal targeting of TCAs from the dorsal lateral geniculate nucleus. These findings indicate that EMX2 imparts positional information normally associated with caudal cortical areas, such as the primary visual area, that influences the area-specific targeting of TCAs. These results are consistent with a role for EMX2 in areal specification of the neocortex as suggested by recent analyses of Emx2 null mutants.
本研究的一个目标是利用重组腺病毒（AdV）在胚胎新皮质中异位表达Emx2，作为一种功能获得性方法，以大鼠为模型研究其在丘脑皮质轴突（TCA）区域特异性靶向中的作用。首先，我们克隆了大鼠Emx2全长编码区的cDNA，它是果蝇空泡的同源物。我们还利用该序列从基因组DNA中确定了小鼠Emx2的全长编码区。我们对Emx2表达的分析表明，在大鼠中，正如在小鼠中所报道的那样，在整个皮质神经发生过程中，Emx2在皮质中呈从高尾端到低嘴端、从高内侧到低外侧的梯度表达，并且表达主要局限于神经上皮中的祖细胞。我们还对携带CAG/LacZ表达构建体的复制缺陷型重组5型腺病毒（AdV）在胚胎皮质神经发生的不同阶段注射到大脑半球侧脑室后感染的细胞分布进行了分析。AdV感染的细胞沿切线广泛分布，但其层状分布受到不同程度的限制，并反映了皮质神经元产生的时间顺序。这一发现表明，AdV主要感染脑室区的祖细胞，这导致其直接后代被优先标记，并感染最近进入有丝分裂后期且尚未远离脑室表面的细胞。然后我们表明，AdV介导的异位Emx2表达导致背侧外侧膝状体核的TCA在皮质内的异常路径寻找和区域靶向。这些发现表明，EMX2赋予了通常与尾侧皮质区域（如初级视觉区）相关的位置信息，该信息影响TCA的区域特异性靶向。这些结果与最近对Emx2基因敲除突变体的分析所表明的EMX2在新皮质区域特化中的作用一致。
