Dept. of Biopathology, Tor Vergata University of Rome, Rome, Italy.
Neurobiol Dis. 2012 Jan;45(1):264-71. doi: 10.1016/j.nbd.2011.08.010. Epub 2011 Aug 18.
Myotonic dystrophy type 1 (DM1) is a complex multisystemic disorder caused by an expansion of a CTG repeat located at the 3' untranslated region (UTR) of DMPK on chromosome 19q13.3. Aberrant messenger RNA (mRNA) splicing of several genes has been reported to explain some of the symptoms of DM1 including insulin resistance, muscle wasting and myotonia. In this paper we analyzed the expression of the MYH14 mRNA and protein in the muscle of DM1 patients (n=12) with different expansion lengths and normal subjects (n=7). The MYH14 gene is located on chromosome 19q13.3 and encodes for one of the heavy chains of the so called class II "nonmuscle" myosins (NMHCII). MYH14 has two alternative spliced isoforms: the inserted isoform (NMHCII-C1) which includes 8 amino acids located in the globular head of the protein, not encoded by the non inserted isoform (NMHCII-C0). Results showed a splicing unbalance of the MYH14 gene in DM1 muscle, with a prevalent expression of the NMHCII-C0 isoform more marked in DM1 patients harboring large CTG expansions. Minigene assay indicated that levels of the MBNL1 protein positively regulates the inclusion of the MYH14 exon 6. Quantitative analysis of the MYH14 expression revealed a significant reduction in the DM1 muscle samples, both at mRNA and protein level. No differences were found between DM1 and controls in the skeletal muscle localization of MYH14, obtained through immunofluorescence analysis. In line with the thesis of an "RNA gain of function" hypothesis described for the CTG mutation, we conclude that the alterations of the MYH14 gene may contribute to the DM1 molecular pathogenesis.
肌强直性营养不良 1 型（DM1）是一种复杂的多系统疾病，由位于 19 号染色体 19q13.3 上 DMPK 基因 3'非翻译区（UTR）的 CTG 重复扩增引起。据报道，几种基因的信使 RNA（mRNA）剪接异常可以解释 DM1 的一些症状，包括胰岛素抵抗、肌肉萎缩和肌强直。在本文中，我们分析了不同扩增长度的 DM1 患者（n=12）和正常受试者（n=7）肌肉中的 MYH14 mRNA 和蛋白表达。MYH14 基因位于 19 号染色体 19q13.3 上，编码所谓的 II 类“非肌肉”肌球蛋白（NMHCII）的一个重链。MYH14 有两种选择性剪接异构体：插入异构体（NMHCII-C1），包含位于蛋白质球状头部的 8 个氨基酸，不被非插入异构体（NMHCII-C0）编码。结果显示 DM1 肌肉中 MYH14 基因的剪接失衡，NMHCII-C0 异构体的表达更为明显，在携带较大 CTG 扩增的 DM1 患者中更为明显。小基因实验表明，MBNL1 蛋白的水平正向调节 MYH14 外显子 6 的包含。通过定量分析 MYH14 的表达，我们发现 DM1 肌肉样本的 mRNA 和蛋白水平均显著降低。通过免疫荧光分析，在 MYH14 在骨骼肌中的定位方面，DM1 和对照组之间没有发现差异。与 CTG 突变描述的“RNA 获得功能”假说一致，我们得出结论，MYH14 基因的改变可能有助于 DM1 的分子发病机制。
