Faculty of Medicine, Department of Biochemistry, Microbiology and Immunology, University of Ottawa, 451 Smyth Road, Ottawa, Ontario, K1H 8M5, Canada.
Ottawa Institute of Systems Biology, Ottawa, Ontario, Canada.
Skelet Muscle. 2021 Nov 19;11(1):26. doi: 10.1186/s13395-021-00281-6.
The Six1 transcription factor is implicated in controlling the development of several tissue types, notably skeletal muscle. Six1 also contributes to muscle metabolism and its activity is associated with the fast-twitch, glycolytic phenotype. Six1 regulates the expression of certain genes of the fast muscle program by directly stimulating their transcription or indirectly acting through a long non-coding RNA. We hypothesized that additional mechanisms of action of Six1 might be at play.
A combined analysis of gene expression profiling and genome-wide location analysis data was performed. Results were validated using in vivo RNA interference loss-of-function assays followed by measurement of gene expression by RT-PCR and transcriptional reporter assays.
The Slc16a10 gene, encoding the thyroid hormone transmembrane transporter MCT10, was identified as a gene with a transcriptional enhancer directly bound by Six1 and requiring Six1 activity for full expression in adult mouse tibialis anterior, a predominantly fast-twitch muscle. Of the various thyroid hormone transporters, MCT10 mRNA was found to be the most abundant in skeletal muscle, and to have a stronger expression in fast-twitch compared to slow-twitch muscle groups. Loss-of-function of MCT10 in the tibialis anterior recapitulated the effect of Six1 on the expression of fast-twitch muscle genes and led to lower activity of a thyroid hormone receptor-dependent reporter gene.
These results shed light on the molecular mechanisms controlling the tissue expression profile of MCT10 and identify modulation of the thyroid hormone signaling pathway as an additional mechanism by which Six1 influences skeletal muscle metabolism.
Six1 转录因子参与控制几种组织类型的发育，特别是骨骼肌。Six1 还参与肌肉代谢，其活性与快肌纤维、糖酵解表型有关。Six1 通过直接刺激其转录或通过长非编码 RNA 间接作用来调节某些快肌程序的基因表达。我们假设 Six1 可能还有其他作用机制。
对基因表达谱和全基因组定位分析数据进行了综合分析。使用体内 RNA 干扰功能丧失测定法验证结果，然后通过 RT-PCR 和转录报告基因测定法测量基因表达。
Slc16a10 基因，编码甲状腺激素跨膜转运体 MCT10，被鉴定为一种基因，其转录增强子直接被 Six1 结合，并需要 Six1 活性才能在成年小鼠胫骨前肌（主要为快肌纤维）中完全表达。在各种甲状腺激素转运体中，MCT10 mRNA 在骨骼肌中含量最丰富，在快肌纤维中比慢肌纤维表达更强。MCT10 在胫骨前肌中的功能丧失复制了 Six1 对快肌纤维基因表达的影响，并导致甲状腺激素受体依赖性报告基因的活性降低。
这些结果揭示了控制 MCT10 组织表达谱的分子机制，并确定了甲状腺激素信号通路的调节是 Six1 影响骨骼肌代谢的另一种机制。
