In wild-type males, REF-1::GFP can be detected in V6- and T-derived seam cells during the L1 and L2 larval stages. After L2, however, REF-1::GFP is undetectable in the V ray lineage. By contrast, in
mab-3 mutant males, REF-1::GFP expres- sion in the seam persists in the L3 and later stages. This pattern of REF-1::GFP expression provides evidence that
ref-1 is negatively regulated by MAB-3 in male seam lineages at the time of V ray specification. The regulation of REF-1::GFP by MAB-3 in the T ray lineage is not unexpected, as there is a weak requirement for
mab-3 in T ray development.