Philpott A, Friend S H
Massachusetts General Hospital Cancer Center, Charlestown 02119.
Mol Cell Biol. 1994 Jul;14(7):5000-9. doi: 10.1128/mcb.14.7.5000-5009.1994.
The transcription factor E2F has been implicated in cell cycle control by virtue of its association with cyclins, cyclin-dependent kinases, and pRb-related tumor suppressor gene products. Eggs and embryos from the frog Xenopus laevis have been used to investigate the characteristics of E2F-like molecules in the Xenopus cell cycle and throughout early development. We find multiple E2F species in Xenopus eggs, at least one of which is modified by phosphorylation. The vast majority of E2F remains in the free form throughout the very early embryonic cell cycle, and it also remains predominantly free until some time after the mid-blastula transition, the onset of zygotic transcription. At this time, E2F complexes significantly to pRb but not to cdk2, although cdk2 binding is found in tissue culture cells from a very advanced stage in embryogenesis. This suggests that the complexing of E2F to cyclins, cyclin-dependent kinases, and tumor suppressor gene products may be controlled separately in early Xenopus development. Thus, the association of E2F with other molecules may not result solely from processes affecting cell cycle progression but may also reflect developmental and differentiation cues.
转录因子E2F因其与细胞周期蛋白、细胞周期蛋白依赖性激酶以及与pRb相关的肿瘤抑制基因产物的关联而涉及细胞周期调控。来自非洲爪蟾的卵和胚胎已被用于研究爪蟾细胞周期及整个早期发育过程中E2F样分子的特性。我们在爪蟾卵中发现了多种E2F物种，其中至少有一种被磷酸化修饰。在非常早期的胚胎细胞周期中，绝大多数E2F保持游离形式，并且在囊胚中期转换（合子转录开始）后的一段时间内也主要保持游离状态。此时，E2F与pRb显著结合，但不与cdk2结合，尽管在胚胎发育非常晚期的组织培养细胞中发现了cdk2结合。这表明在爪蟾早期发育过程中，E2F与细胞周期蛋白、细胞周期蛋白依赖性激酶以及肿瘤抑制基因产物的结合可能是分别受到调控的。因此，E2F与其他分子的关联可能并非仅仅源于影响细胞周期进程的过程，还可能反映发育和分化线索。
