Worm Breeder's Gazette 11(1): 50
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.
I have been screening sterile-unc mutants of C. elegans in an attempt to find genes involved in the control of the cell-cycle in all lineages. Sterile-uncs have broad ranging defects in postembryonic lineages. They have a characteristic and easily recognizable phenotype. They are thin, uncoordinated and the gonad is small or absent. They are also vulvaless or have a protruding vulva. Some examples of sterile-uncs are lin-5, n to have defects in cell division. In lin-5 post embryonic cell cycles continue but cell division fails resulting in cells with large polyploid nuclei. In lin-6 larvae cells continue to divide without DNA replication. It is likely that the products of the lin-5 and lin- 6 genes are required at every cell division and that homozygous mutant worms survive embryogenesis on maternal product. This would run out before L1 lethargus resulting in the failure of all subsequent cell divisions. It seems reasonable to suppose that mutations which result in cell-cycle arrest would also fall into the class of sterile-uncs. There is a fairly large class of genes which can be mutated to give the sterile-unc phenotype. After EMS mutagenesis approximately one in 25 F1s will produce 1/4 sterile unc-progeny. I screened approximately 5000 F1 clones and picked about 190 sterile-unc mutants. Seventy of these were screened using DAPI staining. I was looking for worms with too few ventral cord nuclei but no obvious defects in mitosis. The vast majority had large polyploid cells similar to lin-5, some had other cell division defects, but none were good candidates for cell- cycle arrest mutants. It is possible that mutation in cell-cycle control genes does not result in a sterile-unc phenotype or that they are simply hidden within the much larger class of mitosis mutants. I also screened the sterile-uncs for temperature sensitivity. The cell division phenotypes of mitotic mutants would be difficult to study in the small cells of an L1 larva. If temperature sensitive sterile uncs could be obtained it may be possible to study their phenotype in the large cells of the early embryo. I obtained six temperature-sensitive sterile uncs from a total of 190 mutants but only one of these, 'sterile unc-5', could be obtained as a homozygous strain. In homozygous sterile unc-5 mutants at the nonpermissive temperature all cell divisions, including early embryonic cell divisions, fail, without cell-cycle arrest. The frequency at which homozygous viable ts sterile unc strains can be obtained is too low to make this approach useful in the study of many mitotic mutants.