Takahashi Chiaki, Bronson Roderick T, Socolovsky Merav, Contreras Bernardo, Lee Kwang Youl, Jacks Tyler, Noda Makoto, Kucherlapati Raju, Ewen Mark E
Department of Medical Oncology and Medicine, Dana-Farber Cancer Institute and Harvard Medical School, Boston, MA 02115, USA.
Mol Cell Biol. 2003 Aug;23(15):5256-68. doi: 10.1128/MCB.23.15.5256-5268.2003.
The product of the retinoblastoma tumor suppressor gene (Rb) can control cell proliferation and promote differentiation. Murine embryos nullizygous for Rb die midgestation with defects in cell cycle regulation, control of apoptosis, and terminal differentiation of several tissues, including skeletal muscle, nervous system, and lens. Previous cell culture-based experiments have suggested that the retinoblastoma protein (pRb) and Ras operate in a common pathway to control cellular differentiation. Here we have tested the hypothesis that the proto-oncogene N-ras participates in Rb-dependent regulation of differentiation by generating and characterizing murine embryos deficient in both N-ras and Rb. We show that deletion of N-ras rescues a unique subset of the developmental defects associated with nullizygosity of Rb, resulting in a significant extension of life span. Rb(-/-); N-ras(-/-) skeletal muscle has normal fiber density, myotube length and thickness, in contrast to Rb-deficient embryos. Additionally, Rb(-/-); N-ras(-/-) muscle shows a restoration in the expression of the late muscle-specific gene MCK, and this correlates with a significant potentiation of MyoD transcriptional activity in Rb(-/-); N-ras(-/-), compared to Rb(-/-) myoblasts in culture. The improved differentiation of skeletal muscle in Rb(-/-); N-ras(-/-) embryos occurs despite evidence of deregulated proliferation and apoptosis, as seen in Rb-deficient animals. Our findings suggest that the control of differentiation and proliferation by Rb are genetically separable.
视网膜母细胞瘤抑癌基因（Rb）的产物可控制细胞增殖并促进分化。Rb基因纯合缺失的小鼠胚胎在妊娠中期死亡，伴有细胞周期调控、细胞凋亡控制以及包括骨骼肌、神经系统和晶状体在内的多种组织的终末分化缺陷。先前基于细胞培养的实验表明，视网膜母细胞瘤蛋白（pRb）和Ras在一条共同途径中发挥作用以控制细胞分化。在此，我们通过构建和鉴定同时缺乏N-ras和Rb的小鼠胚胎，来检验原癌基因N-ras参与Rb依赖的分化调控这一假说。我们发现，N-ras的缺失挽救了与Rb纯合缺失相关的一部分独特的发育缺陷，从而显著延长了寿命。与Rb基因缺陷的胚胎不同，Rb(-/-); N-ras(-/-)小鼠的骨骼肌具有正常的纤维密度、肌管长度和厚度。此外，Rb(-/-); N-ras(-/-)小鼠的肌肉中晚期肌肉特异性基因MCK的表达有所恢复，并且这与培养的Rb(-/-); N-ras(-/-)成肌细胞中MyoD转录活性的显著增强相关，而与Rb(-/-)成肌细胞相比。尽管如在Rb基因缺陷动物中所见，存在增殖和凋亡失调的证据，但Rb(-/-); N-ras(-/-)胚胎中骨骼肌的分化仍得到改善。我们的研究结果表明，Rb对分化和增殖的控制在遗传上是可分离的。
