The C. elegans
srf-6 gene controls timing of expression of surface antigens displayed during the first larval stage. In wild-type, display of the antigen marker can be induced on the surface of stages L2-L4 by altering growth conditions (referred to as Inducible Larval Display or ILD). The
srf-6 mutant phenotype has been described as constitutive larval display (CLD), that is, the antigen marker is displayed constitutively on the surface of
srf-6 mutant worms through stage L4, regardless of growth conditions (Grenache et al 1996). Previous studies of interactions between
srf-6 and genes controlling chemosensation in C. elegans suggest that
srf-6 controls surface antigen switching via a chemosensory response to changes in environmental conditions. Indeed,
srf-6 mutant worms are defective in chemotaxis to both volatile and non-volatile attractants (D. Phu and S. Politz, unpublished observations). To explain the details of the genetic interaction between
srf-6and the cilium-structure mutant
che-3, it is necessary to propose that the
srf-6 gene product functions by inhibiting an unknown component that activates display of the L1 marker antigen at later larval stages. To test whether
tax-4, a gene involved in both chemosensation and dauer formation (Komatsu et al 1996), encodes a component with these characteristics,
tax-4 mutants were tested after growth under different conditions and shown to be ILD-defective. To test a possible role for
tax-4 in the specific model proposed above, a
srf-6;
tax-4 double mutant was constructed and tested for CLD. In the double mutant, a
tax-4 mutation suppresses the CLD phenotype of
srf-6, suggesting that
tax-4 functions downstream of
srf-6 in controlling surface antigen switching. Previous results suggested that
srf-6 functions downstream of
daf-11 (L. Miceli and S. Politz, unpublished), a gene involved in dauer formation and chemosensation that encodes a transmembrane guanylyl cyclase (Vowels and Thomas 1994; Birnby et al 2000). Together with the present results, this suggests that
srf-6 may function to mediate a signal between
daf-11 and the cyclic-nucleotide gated ion channel subunit encoded by
tax-4 (Komatsu et al 1996). Birnby et al (2000) Genetics 155: 85-104. Grenache et al (1996) PNAS 93: 12388-12393. Komatsu et al (1996) Neuron 17: 707-718. Vowels and Thomas (1994) Genetics 138: 303-316.