Worm Breeder's Gazette 8(1): 19
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
A family of mitosis-specific phosphoproteins has been recognized by a monoclonal antibody prepared against HeLa mitotic cell extracts ( Davis et al., PNAS 80:2969, 1983). The importance of these phosphoproteins for mitosis (M) is emphasized by their conserved presence in the wild-type nematode, Caenorhabditis r absence at restrictive temperature in one of the temperature-sensitive embryonic arrest mutants, emb-29(g52) and its allele b262. The mitotic index of wild-type and mutant embryos was determined immunocytochemically. At the 250 to 300-cell stage, wild-type embryos exhibited about 16% immunoreactive cells. In contrast, less than 1% of the cells in mutant embryos arrested at restrictive temperature were immunoreactive. However, when arrested embryos were placed on ice for 3-5 hr, up to 90% of their cells were able to enter mitosis and become immunoreactive. Wild-type embryos reached their maximal mitotic index of about 16% during the 4 C incubation. Hence, emb-29 seems to define a cell division cycle function that arrests embryonic cells close to the G2/M interface. The highly conserved antigenic epitope is associated with a family of high molecular weight polypeptides with major bands at 127, 97 and 77 kd. Nearly all of these proteins copurify with a nuclear-cytoskeleton complex. The nematode, unlike other species, elicits a strong reaction at the asters. As in mammalian cells, antigenic reactivity of these multiple proteins depends on their phosphorylation, since antibody binding is reduced after aIkaline phosphatase treatment. These experiments suggest that the emb-29 mutation affects an essential phosphorylation activity required for progression into M. In addition, several embryonic lethal mutants previously shown to form anucleate cells when cultured at restrictive temperature (Hecht et al., (1982) Develop. Biol. 94, 183-191.) could be stained with the mitosis-specific antibody over regions that did not stain for nuclear DNA. This demonstrates that the mitosis-specific protein complex may be prelocalized independently of nuclear DNA and provides additional support for the earlier notion that cytokinesis may also occur independently of nuclear division.