Laboratory of Brain Development and Evolution, Department of Experimental Medicine, Faculty of Medicine, University of Lleida, Institute of Biomedical Research of Lleida, 25008 Lleida, Spain.
Cereb Cortex. 2010 Aug;20(8):1788-98. doi: 10.1093/cercor/bhp242. Epub 2009 Nov 18.
Reelin-expressing Cajal-Retzius (CR) cells are among the earliest generated cells in the mammalian cerebral cortex and are believed to be crucial for both the development and the evolution of a laminated pattern in the pallial wall of the telencephalon. LIM-homeodomain (LIM-hd) transcription factors are expressed during brain development in a highly restricted and combinatorial manner, and they specify regional and cellular identity. We have investigated the expression of the LIM-hd members Lhx1/Lhx2/Lhx5/Lhx6/Lhx9 in the reelin-expressing cells, the pallium, and the regions of origin of CR cells including the cortical hem of 3 amniote species: the mouse, the chick, and the macaque monkey. We found major differences in the combinatorial LIM-hd expression in the marginal zone as well as in the hem. 1) Lhx5 is a "preferential LIM-hd" for CR cells in mammals but not expressed by these cells in chicks. 2) Lhx2 is expressed in the hem of the chick, whereas it is excluded from this region in mouse. 3) Whereas mouse CR cells express Lhx5/Lhx1, their monkey counterparts express 4 of these factors: Lhx1/Lhx2/Lhx5/Lhx9. We discuss our findings in evolutionary terms for the specification of the midline hem and CR cell type and the emergence of the cortical lamination pattern.
表达 Reelin 的 Cajal-Retzius (CR) 细胞是哺乳动物大脑皮层中最早产生的细胞之一，被认为对大脑皮层神经褶壁的层状模式的发育和进化至关重要。LIM 同源域 (LIM-hd) 转录因子在脑发育过程中以高度受限和组合的方式表达，它们决定了区域和细胞的身份。我们研究了 LIM-hd 成员 Lhx1/Lhx2/Lhx5/Lhx6/Lhx9 在表达 Reelin 的细胞、大脑皮层和 CR 细胞起源区域中的表达，包括 3 种羊膜动物的皮质边缘：小鼠、鸡和猕猴。我们发现，在边缘区和皮质边缘区的 LIM-hd 表达组合存在显著差异。1）Lhx5 是哺乳动物 CR 细胞的“优先 LIM-hd”，但在鸡中这些细胞不表达。2）Lhx2 在鸡的皮质边缘区表达，而在小鼠中则被排除在该区域之外。3）虽然小鼠的 CR 细胞表达 Lhx5/Lhx1，但它们的猴子对应物表达其中 4 个因子：Lhx1/Lhx2/Lhx5/Lhx9。我们从进化的角度讨论了我们的发现，这些发现涉及到中线皮质边缘区和 CR 细胞类型的特化以及皮质层状模式的出现。
