Worm Breeder's Gazette 15(1): 77 (October 1, 1997)

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.

fog-1 allele strengths

Amy Shah, Nancy Arno, Ronald Ellis

Department of Biology, University of Michigan, Ann Arbor MI 48109

        fog-1 is a regulatory gene that is required for specification
of spermatogenesis in the germ line of C. elegans.  In fog-1 mutants,
germ cells that would normally develop into sperm become oocytes
instead. Over 60 fog-1 mutations are known.  To better understand how
these mutations affect the fog-1 gene, we have used a sensitive assay
to study the effects that different alleles have on sperm production.
Animals homozygous for a fog-1 mutation could not be used to study
spermatogenesis because these animals do not make any sperm.
Therefore, we used animals with a fog-1 mutation in trans to
fog-1(q253ts) to determine the relative strengths of 16 fog-1 alleles.
q253ts is a weak, temperature sensitive allele that causes XX animals
to become self-sterile at 25 degrees C.  Below 25, however,
fog-1(q253ts) animals are self-fertile.  Therefore, controlling the
temperature at which experiments are run allows us to control the
relative activity of the fog-1(q253ts) gene product.   These
experiments were done at the permissive temperature of 15 degrees C.

In this assay, the percentage of females (which produce no sperm) among
fog-1(?)/fog-1(q253) animals at 15 degrees C served as a measure of
fog-1 allele strength.  The null phenotype was defined using qDf4, a
deficiency that completely removes the fog-1 gene.  Our results show
that the alleles can be divided into three groups:  null (10-20%
females), weak (0% females), and dominant negative (>30% females).  We
conclude: (1) The deficiency qDf3 behaves like a weak fog-1 allele; (2)
likely null alleles are q325 and q241; (3) the dominant negative
alleles are likely to encode a product that interferes with the
specification of spermatogenesis, which suggests that FOG-1 might bind
to itself or another protein.

Although fog-1 is required for spermatogenesis in both males and
hermaphrodites, it is possible that it interacts with different
proteins in the two sexes.  To determine the effect of dominant
negative alleles on spermatogenesis in males, we are conducting sperm
counts in fog-1(?)/fog-1(q253ts) worms.  L4 males of the desired
genotype were picked to separate plates to ensure that no sperm were
lost by mating.  When the males reached adulthood and had switched to
producing oocytes, DAPI staining was used to count sperm under
fluorescent microscopy.  Initial data suggests that dominant negative
alleles of fog-1 have the greatest effect on spermatogenesis in males,
just as in hermaphrodites.

fog-1(?)/fog-1(q253) XX at 15 C       fog-1(?)/fog-1(q253) XO at 15 C

allele     %fem   #herm   %fem         allele      average # of sperm
q253ts       0     105    0.00          q187            27 +/- 9
oz15ts       0      22    0.00          q493            50 +/- 32
qDf3         0      88    0.00          e2121           86 +/- 22
e2121       13     146    8.18          q325           115 +/- 9
qDf4         5      45   10.00
q325        13      93   12.26
q241        14      84   14.29
q242        20      78   20.41
q491        44      90   32.84
q218        28      40   41.18
q507        29      21   58.00
q180        67      38   63.81
q492        21       7   75.00
q254       133      12   91.72
q187       198       3   98.51
q493       102       1   99.03