Shoemaker S D, Ryan A F, Lieber R L
Departments of Orthopaedics, Bioengineering and Surgery/Otolaryngology, University of California and Veterans Administration Medical Centers, San Diego, Calif., USA.
Cells Tissues Organs. 1999;165(1):10-5. doi: 10.1159/000016668.
mRNAs encoding four myosin heavy chain (MHC) isoforms were localized in rat skeletal muscle fibers by in situ hybridization. The ratio of MHC transcript signal in the fiber core compared to the fiber periphery was quantified using image analysis. Two distinct patterns of subcellular localization were observed. Type 1 (beta-cardiac) and type 2A MHC mRNAs were located preferentially in the muscle fiber periphery, while type 2B and type 2X mRNAs were distributed homogeneously across the fiber cross section. Since most normal muscle fibers express only a single MHC isoform, this difference in mRNA distribution could reflect either variation in the localization of the synthetic apparatus across different fiber types or differences in the trafficking of different MHC transcripts. To examine the basis for the observed differential distribution in normal muscles, mRNA distribution was assessed in muscle fibers that coexpressed multiple isoforms of the fast MHCs (i.e. types 2A, 2X and 2B), which occurred either in the combination type 2A/2X or type 2X/2B. The quantitative mRNA distribution seen in muscle fibers expressing a single isoform was not significantly different compared to that observed for mRNAs coexpressed in the same fiber (p > 0.6). Given the size similarity and homology of our riboprobes, these data suggest that their subcellular localization may be determined by relatively small differences in the sequences of the mRNAs, perhaps by differential binding of RNA sequence motifs to cytoskeletal elements.
通过原位杂交技术，对编码四种肌球蛋白重链（MHC）亚型的信使核糖核酸（mRNA）在大鼠骨骼肌纤维中的定位进行了研究。利用图像分析技术，对纤维核心与纤维周边的MHC转录本信号比值进行了定量分析。观察到两种不同的亚细胞定位模式。1型（β-心脏型）和2A型MHC mRNA优先位于肌纤维周边，而2B型和2X型mRNA则均匀分布于纤维横截面积。由于大多数正常肌纤维仅表达单一的MHC亚型，这种mRNA分布的差异可能反映了不同纤维类型中合成装置定位的变化，或者不同MHC转录本运输的差异。为了研究正常肌肉中观察到的差异分布的基础，对共表达多种快速MHC亚型（即2A、2X和2B型）的肌纤维中的mRNA分布进行了评估，这些亚型以2A/2X或2X/2B组合形式出现。与在同一纤维中共表达的mRNA相比，表达单一亚型的肌纤维中定量的mRNA分布没有显著差异（p>0.6）。鉴于我们的核糖探针大小相似且具有同源性，这些数据表明它们的亚细胞定位可能由mRNA序列中相对较小的差异决定，也许是通过RNA序列基序与细胞骨架元件的差异结合来实现的。
