Hallauer P L, Bradshaw H L, Hastings K E
Montreal Neurological Institute, McGill University, Quebec, Canada.
Development. 1993 Nov;119(3):691-701. doi: 10.1242/dev.119.3.691.
We analyzed, in transgenic mice, the cellular expression pattern of the quail fast skeletal muscle troponin I (TnIfast) gene and of a chimeric reporter construct in which quail TnIfast DNA sequences drive expression of E. coli beta-galactosidase (beta-gal). Both constructs were actively expressed in skeletal muscle and specifically in fast, as opposed to slow, muscle fibers. Unexpectedly, both constructs showed a marked differential expression among the adult fast fiber subtypes according to the pattern IIB > IIX > IIA. This expression pattern was consistent in multiple lines and differed from the endogenous mouse TnIfast pattern, which shows approximately equal expression in all fast fibers. These observations indicate that distinct regulatory mechanisms contribute to high-level expression of TnIfast in the various fast fiber subtypes and suggest that the outwardly simple pattern of equal expression in all fast fiber types shown by the endogenous mouse TnIfast gene is based on an intricate system of counterbalancing mechanisms. The adult expression pattern of the TnIfast/beta-gal construct emerged in a two-stage developmental process. Differential expression in fast versus slow fibers was evident in neonatal animals, although expression in fast fibers was relatively weak and homogeneous. During the first two weeks of postnatal life, expression in maturing IIB fibers was greatly increased whereas that in IIA/IIX fibers remained weak, giving rise to marked differential expression among fast fiber types. Thus at least two serially acting (pre- and post-natal) fiber-type-specific regulatory mechanisms contribute to high-level gene expression in adult fast muscle fibers. Unexpected similarities between TnIfast transgene expression and that of the myosin heavy chain gene family (which includes differentially expressed IIB-, IIX- and IIA-specific members) suggest that similar mechanisms may regulate adult fast muscle gene expression in a variety of unrelated muscle gene families.
我们在转基因小鼠中分析了鹌鹑快肌肌钙蛋白I（TnIfast）基因以及一个嵌合报告构建体的细胞表达模式，该嵌合报告构建体中鹌鹑TnIfast DNA序列驱动大肠杆菌β-半乳糖苷酶（β-gal）的表达。两种构建体均在骨骼肌中活跃表达，且特异性地在快肌纤维而非慢肌纤维中表达。出乎意料的是，根据IIB > IIX > IIA模式，两种构建体在成年快肌纤维亚型中均表现出明显的差异表达。这种表达模式在多个品系中是一致的，并且与内源性小鼠TnIfast模式不同，内源性小鼠TnIfast模式在所有快肌纤维中表达大致相等。这些观察结果表明，不同的调控机制有助于TnIfast在各种快肌纤维亚型中的高水平表达，并表明内源性小鼠TnIfast基因在所有快肌纤维类型中表现出的表面上简单的相等表达模式是基于一个复杂的平衡机制系统。TnIfast/β-gal构建体的成年表达模式在一个两阶段的发育过程中出现。快肌纤维与慢肌纤维之间的差异表达在新生动物中很明显，尽管快肌纤维中的表达相对较弱且均匀。在出生后的前两周，成熟IIB纤维中的表达大幅增加，而IIA/IIX纤维中的表达仍然较弱，导致快肌纤维类型之间出现明显的差异表达。因此，至少有两种相继作用（出生前和出生后）的纤维类型特异性调控机制有助于成年快肌纤维中的高水平基因表达。TnIfast转基因表达与肌球蛋白重链基因家族（包括差异表达的IIB、IIX和IIA特异性成员）的表达之间意外的相似性表明，类似的机制可能调节各种不相关肌肉基因家族中的成年快肌基因表达。
