Zacksenhaus E, Jiang Z, Chung D, Marth J D, Phillips R A, Gallie B L
Department of Molecular and Medical Genetics, University of Toronto, Ontario, Canada.
Genes Dev. 1996 Dec 1;10(23):3051-64. doi: 10.1101/gad.10.23.3051.
Mice deficient for the RB gene (RB-/-), prior to death at embryonic day 14.5, show increased cell death in all tissues that normally express RB1: the nervous system, liver, lens, and skeletal muscle precursor cells. We have generated transgenic mice (RBlox) that express low levels of pRb, driven by an RB1 minigene. RBlox/RB-/- mutant fetuses die at birth with specific skeletal muscle defects, including increased cell death prior to myoblast fusion, shorter myotubes with fewer myofibrils, reduced muscle fibers, accumulation of elongated nuclei that actively synthesized DNA within the myotubes, and reduction in expression of the late muscle-specific genes MCK and MRF4. Thus, insufficient pRb results in failure of myogenesis in vivo, manifest in two ways. First, the massive apoptosis of myoblasts implicates a role of pRb in cell survival. Second, surviving myotubes failed to develop normally and accumulated large polyploid nuclei, implicating pRb in permanent withdrawal from the cell cycle. These results demonstrate a role for pRb during terminal differentiation of skeletal muscles in vivo and place pRb at a nodal point that controls cell proliferation, differentiation, and death.
RB基因缺陷型小鼠（RB-/-）在胚胎第14.5天死亡前，在所有正常表达RB1的组织中均表现出细胞死亡增加，这些组织包括神经系统、肝脏、晶状体和骨骼肌前体细胞。我们构建了转基因小鼠（RBlox），其由RB1小基因驱动表达低水平的pRb。RBlox/RB-/-突变胎儿在出生时死亡，伴有特定的骨骼肌缺陷，包括成肌细胞融合前细胞死亡增加、肌管较短且肌原纤维较少、肌纤维减少、肌管内积极合成DNA的伸长细胞核积聚以及晚期肌肉特异性基因MCK和MRF4表达降低。因此，pRb不足导致体内肌生成失败，表现为两种方式。首先，成肌细胞的大量凋亡表明pRb在细胞存活中起作用。其次，存活的肌管未能正常发育并积聚大量多倍体细胞核，这表明pRb在细胞周期的永久退出中起作用。这些结果证明了pRb在体内骨骼肌终末分化过程中的作用，并将pRb置于控制细胞增殖、分化和死亡的节点上。
