Ohsawa Natsumi, Koebis Michinori, Mitsuhashi Hiroaki, Nishino Ichizo, Ishiura Shoichi
Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1, Komaba, Meguro-ku, Tokyo, 153-8902, Japan.
Genes Cells. 2015 Feb;20(2):121-34. doi: 10.1111/gtc.12201. Epub 2014 Nov 18.
Myotonic dystrophy type 1 (DM1) is an RNA-mediated disorder characterized by muscle weakness, cardiac defects and multiple symptoms and is caused by expanded CTG repeats within the 3' untranslated region of the DMPK gene. In this study, we found abnormal splicing of actin-binding LIM protein 1 (ABLIM1) in skeletal muscles of patients with DM1 and a DM1 mouse model (HSA(LR) ). An exon 11 inclusion isoform is expressed in skeletal muscle and heart of non-DM1 individuals, but not in skeletal muscle of patients with DM1 or other adult human tissues. Moreover, we determined that ABLIM1 splicing is regulated by several splice factors, including MBNL family proteins, CELF1, 2 and 6, and PTBP1, using a cellular splicing assay. MBNL proteins promoted the inclusion of ABLIM1 exon 11, but other proteins and expanded CUG repeats repressed exon 11 of ABLIM1. This result is consistent with the hypothesis that MBNL proteins are trapped by expanded CUG repeats and inactivated in DM1 and that CELF1 is activated in DM1. However, activation of PTBP1 has not been reported in DM1. Our results suggest that the exon 11 inclusion isoform of ABLIM1 may have a muscle-specific function, and its abnormal splicing could be related to muscle symptoms of DM1.
1型强直性肌营养不良症（DM1）是一种由RNA介导的疾病，其特征为肌肉无力、心脏缺陷及多种症状，由DMPK基因3'非翻译区内CTG重复序列扩增所致。在本研究中，我们发现DM1患者及DM1小鼠模型（HSA(LR)）骨骼肌中肌动蛋白结合LIM蛋白1（ABLIM1）的剪接异常。11号外显子包含异构体在非DM1个体的骨骼肌和心脏中表达，但在DM1患者的骨骼肌或其他成人组织中不表达。此外，我们通过细胞剪接试验确定ABLIM1剪接受多种剪接因子调控，包括MBNL家族蛋白、CELF1、2和6以及PTBP1。MBNL蛋白促进ABLIM1 11号外显子的包含，但其他蛋白和扩增的CUG重复序列抑制ABLIM1的11号外显子。这一结果与以下假说一致：MBNL蛋白被扩增的CUG重复序列捕获并在DM1中失活，而CELF1在DM1中被激活。然而，DM1中尚未报道PTBP1的激活情况。我们的结果表明，ABLIM1的11号外显子包含异构体可能具有肌肉特异性功能，其异常剪接可能与DM1的肌肉症状有关。
