Muralikrishna B, Dhawan J, Rangaraj N, Parnaik V K
Centre for Cellular and Molecular Biology, Hyderabad 500 007, India.
J Cell Sci. 2001 Nov;114(Pt 22):4001-11. doi: 10.1242/jcs.114.22.4001.
Intranuclear lamin foci or speckles have been observed in various cell types. In order to explore the possibility of changes in internal lamin organization during muscle differentiation, we have examined the appearance of A-type lamin speckles that associate with RNA splicing factor speckles in C2C12 myoblasts and myotubes. Lamin speckles were observed in dividing myoblasts but disappeared early during the course of differentiation in postmitotic myocytes, and were absent in myotubes and muscle fibers. However, no changes were seen in the typical peripheral organization of lamins A/C or B1 or in RNA splicing factor speckles. Lamin speckles were also absent in quiescent myoblasts but reappeared as cells were reactivated to enter the cell cycle. These changes were not observed in other quiescent cell types. Immunoblot analysis indicated that the abundance and migration of lamins A and C was not altered in differentiated myoblasts. When myotube or quiescent myoblast nuclei were extracted with nucleases and detergent, a uniformly stained internal lamina was revealed, indicating that lamins A/C were antigenically masked in these cells, probably owing to structural reorganization of the lamina during differentiation or quiescence. Our results suggest that muscle cell differentiation is accompanied by regulated rearrangements in the organization of the A-type lamins.
在多种细胞类型中都观察到了核内核纤层蛋白聚集区或斑点。为了探究肌肉分化过程中核纤层内部组织变化的可能性，我们检测了与RNA剪接因子斑点相关的A型核纤层蛋白斑点在C2C12成肌细胞和肌管中的出现情况。在分裂的成肌细胞中观察到了核纤层蛋白斑点，但在有丝分裂后肌细胞的分化过程中早期就消失了，在肌管和肌纤维中不存在。然而，A型、C型核纤层蛋白或B1型核纤层蛋白的典型外周组织以及RNA剪接因子斑点均未发生变化。静止的成肌细胞中也不存在核纤层蛋白斑点，但当细胞重新激活进入细胞周期时又会重新出现。在其他静止细胞类型中未观察到这些变化。免疫印迹分析表明，分化的成肌细胞中A型和C型核纤层蛋白的丰度和迁移率没有改变。当用核酸酶和去污剂提取肌管或静止成肌细胞核时，会显示出均匀染色的内核层，这表明A型、C型核纤层蛋白在这些细胞中被抗原性掩盖，可能是由于分化或静止过程中核层的结构重组所致。我们的结果表明，肌肉细胞分化伴随着A型核纤层蛋白组织的调控性重排。
