Mechanobiology Institute, National University of Singapore, Singapore, Singapore.
MRC London Institute of Medical Science, Imperial College London, Hammersmith Campus, Du Cane Road, London, W12 0NN, UK.
Sci Rep. 2020 Feb 3;10(1):1688. doi: 10.1038/s41598-020-58655-7.
Mirtrons are non-canonical miRNAs arising by splicing and debranching from short introns. A plethora of introns have been inferred by computational analyses as potential mirtrons. Yet, few have been experimentally validated and their functions, particularly in relation to their host genes, remain poorly understood. Here, we found that Drosophila larvae lacking either the mirtron miR-1010 or its binding site in the nicotinic acetylcholine receptor β2 (nAcRβ2) 3'UTR fail to grow properly and pupariate. Increase of cortical nAcRβ2 mediated by neural activity elevates the level of intracellular Ca, which in turn activates CaMKII and, further downstream, the transcription factor Adf-1. We show that miR-1010 downregulates nAcRβ2. We reveal that Adf-1 initiates the expression of SKIP, the host gene of miR-1010. Preventing synaptic potentials from overshooting their optimal range requires both SKIP to temper synaptic potentials (incoherent feedforward loop) and miR-1010 to reduce nAcRβ2 mRNA levels (negative feedback loop). Our results demonstrate how a mirtron, in coordination with its host gene, contributes to maintaining appropriate receptor levels, which in turn may play a role in maintaining homeostasis.
Mirtrons 是通过剪接和去分支从短内含子产生的非规范 miRNA。通过计算分析推断出大量的内含子可能是 mirtrons。然而，很少有被实验验证过，它们的功能，特别是与它们的宿主基因的关系，仍然知之甚少。在这里，我们发现缺乏 mirtron miR-1010 或其在烟碱型乙酰胆碱受体β2(nAcRβ2)3'UTR 中的结合位点的果蝇幼虫不能正常生长和化蛹。神经活动增加皮质 nAcRβ2 会提高细胞内 Ca 的水平，进而激活 CaMKII，再下游则激活转录因子 Adf-1。我们表明 miR-1010 下调 nAcRβ2。我们揭示了 Adf-1 启动了 miR-1010 的宿主基因 SKIP 的表达。为了防止突触电位超过其最佳范围，需要 SKIP 来调节突触电位（非相干前馈回路），以及 miR-1010 来降低 nAcRβ2 mRNA 水平（负反馈回路）。我们的结果表明，mirtron 如何与宿主基因协调，有助于维持适当的受体水平，这反过来又可能在维持体内平衡中发挥作用。
