Borycki A G, Li J, Jin F, Emerson C P, Epstein J A
Department of Cell and Developmental Biology, Division of Cardiovascular Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
Development. 1999 Apr;126(8):1665-74. doi: 10.1242/dev.126.8.1665.
In developing vertebrate embryos, Pax3 is expressed in the neural tube and in the paraxial mesoderm that gives rise to skeletal muscles. Pax3 mutants develop muscular and neural tube defects; furthermore, Pax3 is essential for the proper activation of the myogenic determination factor gene, MyoD, during early muscle development and PAX3 chromosomal translocations result in muscle tumors, providing evidence that Pax3 has diverse functions in myogenesis. To investigate the specific functions of Pax3 in development, we have examined cell survival and gene expression in presomitic mesoderm, somites and neural tube of developing wild-type and Pax3 mutant (Splotch) mouse embryos. Disruption of Pax3 expression by antisense oligonucleotides significantly impairs MyoD activation by signals from neural tube/notochord and surface ectoderm in cultured presomitic mesoderm (PSM), and is accompanied by a marked increase in programmed cell death. In Pax3 mutant (Splotch) embryos, MyoD is activated normally in the hypaxial somite, but MyoD-expressing cells are disorganized and apoptosis is prevalent in newly formed somites, but not in the neural tube or mature somites. In neural tube and somite regions where cell survival is maintained, the closely related Pax7 gene is upregulated, and its expression becomes expanded into the dorsal neural tube and somites, where Pax3 would normally be expressed. These results establish that Pax3 has complementary functions in MyoD activation and inhibition of apoptosis in the somitic mesoderm and in repression of Pax7 during neural tube and somite development.
在发育中的脊椎动物胚胎中，Pax3在神经管以及产生骨骼肌的轴旁中胚层中表达。Pax3突变体出现肌肉和神经管缺陷；此外，在早期肌肉发育过程中，Pax3对于肌源性决定因子基因MyoD的正常激活至关重要，并且PAX3染色体易位会导致肌肉肿瘤，这表明Pax3在肌生成中具有多种功能。为了研究Pax3在发育中的具体功能，我们检测了野生型和Pax3突变体（斑点）小鼠胚胎发育过程中前体中胚层、体节和神经管中的细胞存活情况和基因表达。反义寡核苷酸破坏Pax3表达会显著削弱培养的前体中胚层（PSM）中来自神经管/脊索和表面外胚层的信号对MyoD的激活作用，并伴随着程序性细胞死亡的显著增加。在Pax3突变体（斑点）胚胎中，MyoD在下轴体节中正常激活，但表达MyoD的细胞排列紊乱，新形成的体节中普遍存在细胞凋亡，但神经管或成熟体节中不存在。在维持细胞存活的神经管和体节区域，密切相关的Pax7基因上调，其表达扩展到背侧神经管和体节，而这些部位通常是Pax3表达的区域。这些结果表明，Pax3在体节中胚层的MyoD激活和细胞凋亡抑制以及神经管和体节发育过程中对Pax7的抑制方面具有互补功能。
