J Struc Biol 2001(89-95).pdfVIP

Journal of Structural Biology 136, 89–95 (2001) doi:10.1006/jsbi.2001.4425, available online at onNuclear Reconstitution of Plant (Orychophragmus violaceus) Demembranated Sperm in Cell-Free Extracts from Animal (Xenopus laevis) Eggs Ping Lu, 1 Min Ren, and Zhong-He Zhai School of Life Sciences, Peking University, Beijing 100871, ChinaCell-free extracts from animal Xenopus laevis egg could induce chromatin decondensation and pronuclear formation from demembranated plant (Orychophragmus violaceus) sperm. When incu- bated with Xenopus egg extracts, the demem- branated sperm began to swell and then gradually decondensed. The assembly of the nuclear envelope in the reconstituted nuclei was visualized by means of electron microscopy and fluorescence micros- copy. Membrane vesicles fused to form the double envelope around the periphery of the decondensed chromatin. The morphology of the newly formed nuclei, with a double membrane, was similar to that of nuclei after fertilization. The electron micro- graph of the whole-mount prepared nuclear ma- trix–lamina showed the reconstituted nucleus to be filled with a dense network. ? 2001 Elsevier Science (USA) Key Words: cell-free system; egg extracts; nuclear reconstitution; Orychophragmus violaceus; plant sperm; Xenopus laevis. INTRODUCTION Nuclear assembly is a universal phenomenon in life cycles, for example, the nuclear reconstitution after mitosis and meiosis. Once cell division is com- plete, the two filial cells must reassemble the nu- cleus from its component parts. The process of nu- clear assembly is a good model for studying the function and organization of the nucleus. Although much information has emerged about the individual structural components of the nucleus (e.g., nucleo- somes, chromatin loops, and the nuclear envelope and lamina), an integrated picture of the way in which these components interact to form a function- 1 To whom correspondence should be addressed at Department of Cell Biology and Genetics, Sch