He H Y, Gao C, Vrensen G, Zelenka P
National Eye Institute, National Institutes of Health, Bethesda, Maryland, USA.
Dev Dyn. 1998 Jan;211(1):26-34. doi: 10.1002/(SICI)1097-0177(199801)211:1<26::AID-AJA3>3.0.CO;2-9.
Previous work has shown that postmitotic, differentiating fiber cells of the embryonic chicken lens express cyclin B and Cdc2. The present study explores the possible physiological role of these proteins in lens differentiation by examining the developmental regulation of cyclin B/Cdc2 expression and activity in lens fiber cells of embryonic and newborn rats. Cyclin B mRNA and protein were detected not only in the lens epithelium, which contains proliferating cells, but also in postmitotic, differentiating fiber cells. In contrast, cyclin A mRNA and protein were detected only in epithelial cells. Immunoprecipitation with cyclin B antibody coprecipitated Cdc2 from both epithelial and fiber cell extracts. Immunoprecipitates of cyclin B from both epithelial cells and fiber cells showed H1 kinase activity when assayed in vitro, but the developmental pattern of cyclin B-associated kinase activity in these two lens fractions was markedly different. In the epithelium, H1 kinase activity decreased gradually with developmental age in parallel with the decrease in epithelial cell proliferation, whereas, in the fiber cells, kinase activity peaked sharply at embryonic day 18 (E18) and E19. Microscopic examination of rat lenses indicated that peak cyclin B/Cdc2 activity was correlated with changes in chromatin structure and nuclear envelope breakdown in the terminally differentiating primary lens fiber cells. These findings suggest that cyclin B/Cdc2 activity may play an active role in nuclear changes leading to primary fiber cell denucleation.
先前的研究表明,胚胎期鸡晶状体的有丝分裂后分化的纤维细胞表达细胞周期蛋白B和Cdc2。本研究通过检测胚胎期和新生大鼠晶状体纤维细胞中细胞周期蛋白B/Cdc2表达及活性的发育调控,探讨了这些蛋白质在晶状体分化中可能的生理作用。细胞周期蛋白B的mRNA和蛋白不仅在含有增殖细胞的晶状体上皮细胞中被检测到,也在有丝分裂后分化的纤维细胞中被检测到。相比之下,细胞周期蛋白A的mRNA和蛋白仅在上皮细胞中被检测到。用细胞周期蛋白B抗体进行免疫沉淀,可从上皮细胞和纤维细胞提取物中共沉淀出Cdc2。上皮细胞和纤维细胞中细胞周期蛋白B的免疫沉淀物在体外检测时均显示出H1激酶活性,但这两个晶状体组分中与细胞周期蛋白B相关的激酶活性的发育模式明显不同。在上皮细胞中,H1激酶活性随着发育年龄逐渐降低,与上皮细胞增殖的减少平行,而在纤维细胞中,激酶活性在胚胎第18天(E18)和E19时急剧达到峰值。对大鼠晶状体的显微镜检查表明,细胞周期蛋白B/Cdc2活性峰值与终末分化的初级晶状体纤维细胞中染色质结构变化和核膜破裂相关。这些发现表明,细胞周期蛋白B/Cdc2活性可能在导致初级纤维细胞核去核化的核变化中起积极作用。