Kablar B, Krastel K, Ying C, Tapscott S J, Goldhamer D J, Rudnicki M A
Institute for Molecular Biology and Biotechnology, Cancer Research Group, McMaster University, Hamilton, Ontario, L8S 4K1, Canada.
Dev Biol. 1999 Feb 15;206(2):219-31. doi: 10.1006/dbio.1998.9126.
Gene targeting has indicated that the bHLH transcription factors Myf-5 and MyoD are required for myogenic determination because skeletal myoblasts and myofibers are entirely ablated in mouse embryos lacking both Myf-5 and MyoD. Entrance into the skeletal myogenic program during development occurs following the independent transcriptional induction of either Myf-5 or MyoD. To identify sequences required for the de novo induction of MyoD transcription during development, we investigated the expression patterns of MyoD-lacZ transgenes in embryos deficient in both Myf-5 and MyoD. We observed that a 258-bp fragment containing the core of the -20-kb MyoD enhancer activated expression in newly formed somites and limb buds in compound mutant embryos lacking both Myf-5 and MyoD. Importantly, Myf-5- and MyoD-deficient presumptive muscle precursor cells expressing beta-galactosidase were observed to assume nonmuscle fates primarily as precartilage primordia in the trunk and the limbs, suggesting that these cells were multipotential. Therefore, cells are recruited into the MyoD-dependent myogenic lineage through activation of the -20-kb MyoD enhancer and this occurs independently in somites and limb buds.
基因打靶表明，bHLH转录因子Myf-5和MyoD对于肌源性决定是必需的，因为在同时缺乏Myf-5和MyoD的小鼠胚胎中，骨骼肌成肌细胞和肌纤维完全缺失。在发育过程中，进入骨骼肌生成程序是在Myf-5或MyoD的独立转录诱导之后发生的。为了鉴定发育过程中MyoD转录从头诱导所需的序列，我们研究了Myf-5和MyoD均缺失的胚胎中MyoD-lacZ转基因的表达模式。我们观察到，一个包含-20 kb MyoD增强子核心的258 bp片段，在同时缺乏Myf-5和MyoD的复合突变胚胎的新形成的体节和肢芽中激活了表达。重要的是，观察到表达β-半乳糖苷酶的Myf-5和MyoD缺陷型推定肌肉前体细胞主要作为躯干和四肢的软骨前原基而呈现非肌肉命运，这表明这些细胞具有多能性。因此，细胞通过-20 kb MyoD增强子的激活而被招募到依赖MyoD的肌源性谱系中，并且这在体节和肢芽中独立发生。
