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.

Embryonic-arrest Mutant of C. elegans Fails to Phosphorylate Mitosis-Specific Phosphoproteins

R.M. Hecht, M. Berg-Zabelshansky, F.M. Davis

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.