TRANSIENT ARREST OF 3T3 CELLS IN MITOSIS AND INHIBITION OF NUCLEAR LAMIN REASSEMBLY AROUND CHROMATIN INDUCED BY ANTIVIMENTIN ANTIBODIES

We have microinjected anti-vimentin antibodies into nocodazole-arreste d, prometaphasic 3T3 cells. Exit of injected and control cells from mi tosis has been assessed at various time points after release from noco dazole by examining the distribution of nuclear lamins, the degree of chromatin condensation and the appearance of daughter cells. It is sho wn here that 1 h after release from nocodazole, the vast majority of c ells injected with control antibodies enter interphase, whereas most o f the cells injected with anti-vimentin antibodies remain prometaphasi c. Microinjection of vimentin-free (MCF-7) cells with anti-vimentin an tibodies does not affect the normal completion of mitosis in the major ity of the cells. The arresting effect on 3T3 cells is dependent on th e concentration of the microinjected anti-vimentin antibodies and can also be detected when Fabs are injected instead of intact IgG. Samplin g at later time points and monitoring of individual microinjected cell s indicate that the antibody-induced effect lasts for 1.5 to 4 h, i.e. , up to 400% longer than the normal mitotic cycle of 3T3 cells. Howeve r, 4 h after release from nocodazole, most of the antibody-arrested ce lls recover and divide successfully. Electron microscopy shows that th e IFs of the microinjected cells are thicker than normal and tend to a nastomose. Interestingly, the nuclei of some of the cells that escape the antibody-induced arrest and successfully divide appear segmented o r lobulated. Using a mitotic cell-free system, we further demonstrate that anti-vimentin antibodies interfere with nuclear lamin assembly ar ound chromatin particles. In agreement to the in vivo results, the inh ibitory effect of the antibodies appears to subside with time. Taken t ogether, these data suggest that the remodelling of the vimentin netwo rk which normally takes place during mitosis is an important rearrange ment of the cytoplasm required for efficient nuclear reassembly at the end of cell division.