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.

Sterile-Unc Mutants of C. elegans

David Livingstone

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.