Both
fog-3 and
fog-1 are required to specify that germ cells differentiate as sperm rather than as oocytes. Several facts suggest that they act in response to the sex-determination genes to control this fate. Thus, they are currently the best system for understanding how sexual fates are specified in specific tissues. To understand how a variety of
fog-1 mutations affect the activity of the gene, we have assayed
fog-1(x)/fog-1
(q253ts) animals for self-fertility at 15 degrees C. Our results suggest that
fog-1 mutations fall into three classes. First, the deletion qDf3, the temperature-sensitive alleles
q253 and
oz15, and the mutation
e2121 cause a partial loss of
fog-1 activity. Second, the deletion qDf4 (which removes genes on both sides of
fog-1) and the mutations
q241 and
q242 (induced by gamma-rays) are null alleles. Third, mutations such as
q180,
q187,
q491 and
q507 cause a more severe phenotype than does qDf4. These mutations are likely to encode a dominant negative FOG-1 product. These results suggest that FOG-1 binds to another protein required for spermatogenesis. Possible targets are FOG-1 itself, FOG-3, one of the FEM proteins, or an unknown protein. Because
fog-3 appears to encode a protein tyrosine phosphatase, one simple model is that FOG-3 regulates the activity of FOG-1, and FOG-1 in turn controls the transcription of genes needed for spermatogenesis. To test this model we are cloning the
fog-1 gene. Transformation rescue experiments and genetic mapping data indicate that
fog-1 is located in a large region of the YAC Y54E10 that is not represented in cosmid libraries. Pulse-field gels indicate that this gap is approximately 200 kb in size. We have subcloned Y54E10, and are currently screening for clones that identify a re-arrangement in qDf3 DNA, since qDf3 causes only a partial loss of
fog-1 activity. Positive clones will be tested for ability to rescue
fog-1 mutants.