非细胞体系核重建过程中两类膜泡在环形片层及核被膜形成中的作用

非洲爪蟾卵经钙离子载体A 23187激活后,在10,000g下离心得到爪蟾卵提取物。Lambda DNA加入上述提取物可构建出染色质结构,并在染色质表面重建核被膜,同时在染色质外的区域形成环形片层。核被膜与环形片层有相似的发生途径,它们都是由两类在形态、大小、膜结构上有明显差别的膜泡融合而来。首先是直径200nm的圆形小膜泡相互融合成双层膜片层,同时核孔复合体在双层膜上大量装配,以这些双层膜片层为基础,光滑的大膜泡与之融合导致环形片层的扩张与核被膜的成熟。

THE ROLES OF TWO KINDS OF MEMBRANE VESICLES IN THE FORMATION OF ANNULATE LAMELLAE AND NUCLEAR ENVELOPES IN A CELL- FREE SYSTEM FROM XENOPUS EGG EXTRACTS

The eggs of Xenopus laevis were activated to complete their second meiosis and enter interphase by calcium ionophore A 23187. Then they were centrifuged at 10,000g to get activated Xenopus egg extracts. Chromatin structure could form in such an extracts after exogenous Lambda DNA was added, and nuclear envelopes (NEs) could assemble around the chroma-tin. Furthermore, annulate lamellae (AL), a NE-like membrane structure, could form in chromatin-free regions simultaneously. After large amounts of observation and analysis at ultrastructural level, we propose that both AL and NEs assemble in the extracts by the fusion of membrane vesicles. There were two kinds of membrane vesicles in Xenopus egg extracts, small rough vesicles with diameters of 200 nm and large smooth vesicles. They had many differences in morphology, size and membr- ane structure. However, they both participate in the formation of AL and NEs. 200 nm membrane vesicles first fused each other to become parallel double membrane cisternae, nuclear pore complexes assembled in the double membranes in the mean time. The fusion of large smooth vesicles with the double membrane cirternae led to the growth of AL and the maturity of NEs. During the formation of NEs, large smooth vesicles were easily observed to link two neighboring double membrane fragments by fusing with them, so that integrated nuclear envelope could form. 200 nm small rough vesicles could attach to the surface of chromatin to start the assembly of nuclear envelopes, while others could fuse each other at chromatin-free regions and these fusion resulted in the formation of annulate lamellae.