Neville C, Gonzales D, Houghton L, McGrew M J, Rosenthal N
Cardiovascular Research Center, Massachusetts General Hospital, Charlestown 02129-2060, USA.
Dev Genet. 1996;19(2):157-62. doi: 10.1002/(SICI)1520-6408(1996)19:2<157::AID-DVG7>3.0.CO;2-8.
The two proteins encoded by the fast alkali myosin light chain (MLC) 1f/3f locus are developmentally regulated, muscle specific, and expressed exclusively in fast-twitch fibers. Their expression is independently regulated by two separate promoters and a downstream enhancer. Previous studies showed a reporter gene directed by the rat MLC If promoter and MLC enhancer to exhibit correct skeletal muscle-specific expression in transgenic mice during development and to be preferentially expressed in fast-twitch Type IIB fibers [Donoghue et al., (1991) J. Cell B.ol. 115:423-434]. The MLC 3f promoter also directed muscle-specific expression of a CAT reporter gene in adult transgenic mice and showed little dependence upon the enhancer. Here, we show that the MLC 3f promoter also directs transgene expression in the fast-twitch fibers of adult skeletal muscle, but almost exclusively to fiber Types IIA and IIX. MLC 3f transgene expression occurs in only a subset of the fiber types that express the endogenous locus, indicating modular elements included in the transgene confer fiber-specific transcription regulation. MyoD protein was also found to be restricted to fiber Types IIA and IIX, providing evidence for its possible role in mediating fiber-specific gene expression.
快速碱肌球蛋白轻链（MLC）1f/3f基因座编码的两种蛋白质在发育过程中受到调控，具有肌肉特异性，且仅在快肌纤维中表达。它们的表达由两个独立的启动子和一个下游增强子独立调控。先前的研究表明，由大鼠MLC If启动子和MLC增强子指导的报告基因在转基因小鼠发育过程中表现出正确的骨骼肌特异性表达，并优先在快肌IIB型纤维中表达[多诺霍等人，（1991年）《细胞生物学杂志》115:423 - 434]。MLC 3f启动子在成年转基因小鼠中也指导了CAT报告基因的肌肉特异性表达，并且对增强子的依赖性很小。在这里，我们表明MLC 3f启动子也指导转基因在成年骨骼肌的快肌纤维中表达，但几乎只在IIA和IIX型纤维中表达。MLC 3f转基因表达仅发生在内源基因座表达的一部分纤维类型中，表明转基因中包含的模块化元件赋予了纤维特异性转录调控。还发现MyoD蛋白仅限于IIA和IIX型纤维，为其在介导纤维特异性基因表达中的可能作用提供了证据。
