Thierion Elodie, Le Men Johan, Collombet Samuel, Hernandez Céline, Coulpier Fanny, Torbey Patrick, Thomas-Chollier Morgane, Noordermeer Daan, Charnay Patrick, Gilardi-Hebenstreit Pascale
Ecole normale supérieure, PSL Research University, CNRS, Inserm, Institut de Biologie de l'Ecole normale supérieure (IBENS), Paris, France.
Sorbonne Universités, UPMC Univ Paris 06, IFD, Paris, France.
PLoS Genet. 2017 Jul 27;13(7):e1006903. doi: 10.1371/journal.pgen.1006903. eCollection 2017 Jul.
Developmental genes can harbour multiple transcriptional enhancers that act simultaneously or in succession to achieve robust and precise spatiotemporal expression. However, the mechanisms underlying cooperation between cis-acting elements are poorly documented, notably in vertebrates. The mouse gene Krox20 encodes a transcription factor required for the specification of two segments (rhombomeres) of the developing hindbrain. In rhombomere 3, Krox20 is subject to direct positive feedback governed by an autoregulatory enhancer, element A. In contrast, a second enhancer, element C, distant by 70 kb, is active from the initiation of transcription independent of the presence of the KROX20 protein. Here, using both enhancer knock-outs and investigations of chromatin organisation, we show that element C possesses a dual activity: besides its classical enhancer function, it is also permanently required in cis to potentiate the autoregulatory activity of element A, by increasing its chromatin accessibility. This work uncovers a novel, asymmetrical, long-range mode of cooperation between cis-acting elements that might be essential to avoid promiscuous activation of positive autoregulatory elements.
发育基因可包含多个转录增强子，这些增强子同时或相继发挥作用，以实现强大而精确的时空表达。然而，顺式作用元件之间协同作用的潜在机制鲜有文献记载，在脊椎动物中尤为如此。小鼠基因Krox20编码一种转录因子，该因子是发育中后脑两个节段（菱脑节）特化所必需的。在菱脑节3中，Krox20受到由自身调节增强子元件A控制的直接正反馈调节。相比之下，另一个增强子元件C距离较远，有70 kb，从转录开始就有活性，且不依赖KROX20蛋白的存在。在这里，通过增强子敲除和染色质组织研究，我们表明元件C具有双重活性：除了其经典的增强子功能外，它还通过增加染色质可及性，在顺式作用中永久需要以增强元件A的自身调节活性。这项工作揭示了顺式作用元件之间一种新的、不对称的、远程协同模式，这可能是避免正自身调节元件的杂乱激活所必需的。
