Worm Breeder's Gazette 15(1): 78 (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.

Isolation and Characterization of fog-1(q253ts) Suppressors

Suk-Won Jin, Jeff Nicola, Ronald Ellis

Dept. of Biology, University of Michigan, Ann Arbor, MI 48109

Two genes, fog-1 and fog-3 , are essential to specify that germ cells
differentiate as sperm rather than as oocytes.  Several observations
suggest that these genes might directly control sexual fate for germ
cells.  First, fog-1 and fog-3 are required in both sexes for the
production of sperm rather than oocytes.  Second, mutations in either
gene are epistatic to alleles of other known sex determination genes.
Third, mutations in these genes affect only germ cells.  Fourth,
sequence analysis suggests that fog-3 is regulated by TRA-1A, which
acts near the end of the sex-determination pathway.

There are more than 60 known alleles of fog-1, including two
temperature sensitive alleles, fog-1(q253ts) and fog-1(oz15ts).  Males
that are homozygous for fog-1(q253ts) produce sperm at 15 degrees C and
oocytes at 25 degrees C; hermaphrodites produce both sperm and oocytes
at 15 degrees C and only oocytes at 25 degrees C, preventing
self-fertilization.  To identify genes whose products regulate or
interact with FOG-1, we screened for suppressors of fog-1(q253ts).
Such mutations might identify new genes that regulate sexual identity
in germ cells.  If they exist, we might also find mutations that bypass
the need for fog-1.

So far, we have isolated 18 suppressor mutations after screening 40,000
haploid genomes, following exposure to ethyl methanesulfonate (EMS).
The suppressed animals produce both sperm and oocytes at 25 degrees C,
allowing self-fertilization.  All the suppressors, except one, are
recessive, and none are completely penetrant.

Preliminary data indicate that most of these suppressors fall into two
complementation groups.  The alleles v3, v12, v15, v16  and v21 fail to
complement each other, and map in the vicinity of rol-1 on LGII.
Furthermore, the alleles v7, v8, v9, v17, v18, v20, and v23 fail to
complement, and map very near unc-32 on LGIII.  Finally, the alleles
v4, q475, and v11 complement both the sup on II and the sup on III, and
so might identify additional genes. We are just beginning analysis of
the remaining three suppressor mutations.

The fact that suppressor alleles on LGIII are closely linked to unc-32
suggested that they might be weak alleles of mog-1.  To test the
possibility that these mutations on LGIII were novel alleles of mog-1,
we did complementation tests at both 15!C and 25!C using the
mog-1(q223) mutation.  All heterozygous F1 animals were fertile at both
temperatures, suggesting that the suppressor alleles on LGIII might
define a new locus.

We are now using three factor mapping to localize these mutations more
precisely, characterizing the phenotypes of the suppressors in the
absence of fog-1(q253ts), and screening for additional alleles in a
mut-7 background.