During C. elegans male ray development, Hox genes
mab-5 and
egl-5 are required for seam cell V6 to produce rays 2 to 6. Consistent with genetic studies, antibodies and reporter genes show both Hox genes are expressed in V6. How the Hox gene expression pattern is both initiated and maintained in V6 is not clear. Laser ablation experiments show that cell-cell interactions have an effect on
mab-5 expression in V6. During male ray development, posterior seam cell T sends an inhibitory signal to its anterior neighbor V6 to inhibit
mab-5 expression.
pal-1, which encodes a homolog of Drosophila caudal, acts autonomously in V6 to override this inhibitory signal. Thus in
pal-1(
e2091) mutant,
mab-5 is not expressed in V6, and V6 produces alae instead of rays. To identify the signal from seam cell T, as well as other
mab-5 regulatory components, we performed a screen for suppressors of
pal-1(
e2091). We predicted the suppressors should result in activation of Hox genes and this has been found. 19 alleles defining 15 genes were obtained from 4000 genomes screened. We are analyzing 3 of these in detail.
sop-1 X is a recessive maternal effect gene. In the strongest allele,
bx92, 97% of sides have normal V6 rays in a
pal-1 mutant background. Using a
mab-5::GFP reporter, we found
sop-1(
bx92) restores
mab-5 expression in V6. We also have shown the V6 rays in
pal-1(
e2091);
sop-1(
bx92) are dependent on
mab-5 activity. Mosaic analysis indicated
pal-1(+) activity is not required for the generation of V6 rays in
sop-1(
bx92) .
sop-1 does not have any other obvious phenotype in a
pal-1(+) background. We cloned
sop-1 by transformation rescue. It encodes a 3520 amino acid protein, containing a Q rich region. There is one similar uncharacterized human gene product. Unlike
sop-1 mutant, whose effects seem to be restricted to V6,
sop-2(
bx91) II has more global effects on Hox gene expression. In
sop-2(
bx91);
pal-1(+) background, 7% of male sides have rays 2 and 3 transformed to rays 4, 5, and 6, suggesting possible misregulation of
egl-5 in the V6 lineage. In some males and hermaphrodites, there are ectopic ray papillae as well as broken alae. The
sop-2 mutant has other phenotypes, including affects on vulval and hook development. These pleiotropic effects might be due to ectopic expression of Hox genes. Using
mab-5::lacZ and
egl-5::lacZ reporter genes, we found that
mab-5 and
egl-5 are expressed throughout the body in
sop-2(
bx91) mutant. Therefore,
sop-2 is required widely for silencing Hox gene expression.
sop-3(
bx96) I is also a recessive maternal effect mutation. In
sop-3(
bx96);
pal-1(
e2091) mutant, 81% of sides have normal V6 rays. In
sop-3(
bx96);
pal-1(+) background there is a low frequency of ray fusion, and ray 6 is sometimes missing. The ray arrangement is also abnormal.
sop-3 has other phenotypes, such as protruding vulvae and dumpy. The cloning of
sop-2 and
sop-3 is in progress.