Kim Namhee, Park Chungoo, Jeong Yongsu, Song Mi-Ryoung
School of Life Sciences, Cell Dynamics Research Center, Gwangju Institute of Science and Technology, Oryong-dong, Buk-gu, Gwangju, Republic of Korea.
School of Biological Sciences and Technology, Chonnam National University, Yongbong-ro, Buk-gu, Gwangju, Republic of Korea.
PLoS Genet. 2015 Oct 8;11(10):e1005560. doi: 10.1371/journal.pgen.1005560. eCollection 2015 Oct.
Functional diversification of motor neurons has occurred in order to selectively control the movements of different body parts including head, trunk and limbs. Here we report that transcription of Isl1, a major gene necessary for motor neuron identity, is controlled by two enhancers, CREST1 (E1) and CREST2 (E2) that allow selective gene expression of Isl1 in motor neurons. Introduction of GFP reporters into the chick neural tube revealed that E1 is active in hindbrain motor neurons and spinal cord motor neurons, whereas E2 is active in the lateral motor column (LMC) of the spinal cord, which controls the limb muscles. Genome-wide ChIP-Seq analysis combined with reporter assays showed that Phox2 and the Isl1-Lhx3 complex bind to E1 and drive hindbrain and spinal cord-specific expression of Isl1, respectively. Interestingly, Lhx3 alone was sufficient to activate E1, and this may contribute to the initiation of Isl1 expression when progenitors have just developed into motor neurons. E2 was induced by onecut 1 (OC-1) factor that permits Isl1 expression in LMCm neurons. Interestingly, the core region of E1 has been conserved in evolution, even in the lamprey, a jawless vertebrate with primitive motor neurons. All E1 sequences from lamprey to mouse responded equally well to Phox2a and the Isl1-Lhx3 complex. Conversely, E2, the enhancer for limb-innervating motor neurons, was only found in tetrapod animals. This suggests that evolutionarily-conserved enhancers permit the diversification of motor neurons.
运动神经元发生了功能多样化,以便选择性地控制包括头部、躯干和四肢在内的不同身体部位的运动。在此,我们报告称,Isl1(运动神经元身份所需的主要基因)的转录受两个增强子CREST1(E1)和CREST2(E2)控制,这两个增强子可使Isl1在运动神经元中进行选择性基因表达。将绿色荧光蛋白报告基因导入鸡神经管后发现,E1在后脑运动神经元和脊髓运动神经元中具有活性,而E2在控制肢体肌肉的脊髓外侧运动柱(LMC)中具有活性。全基因组染色质免疫沉淀测序(ChIP-Seq)分析与报告基因检测相结合表明,Phox2和Isl1-Lhx3复合物分别与E1结合,并驱动Isl1在后脑和脊髓中的特异性表达。有趣的是,单独的Lhx3就足以激活E1,这可能有助于在祖细胞刚发育成运动神经元时启动Isl1的表达。E2由onecut 1(OC-1)因子诱导,该因子允许Isl1在LMCm神经元中表达。有趣的是,E1的核心区域在进化过程中一直保守,即使在具有原始运动神经元的无颌脊椎动物七鳃鳗中也是如此。从七鳃鳗到小鼠的所有E1序列对Phox2a和Isl1-Lhx3复合物的反应同样良好。相反,用于支配肢体的运动神经元的增强子E2仅在四足动物中发现。这表明进化上保守的增强子允许运动神经元的多样化。