Fig. 4. Generation and fate of the PVT neuron are unaffected in lim-6 ceh-14 double mutants. (A) srq-1::gfp (otIs85) and unc-47::gfp (otIs39) are markers for PVT cell fate. In addition to PVT, srq-1 is expressed in one more tail neuron and several head neurons. The unc-47::gfp constructs labels not only the RMEL/R, RIS, AVL and DVB, as described previously (Eastman et al., 1999), but also the PVT neuron. Expression of the two other PVT cell fate markers used here (B), gpa-2 and pin-2, has been previously documented (Hobert et al., 1999a; Zwaal et al., 1997) and is not shown. (B) Expression of PVT cell fate markers in mutant backgrounds. All alleles shown are molecular nulls. Scoring was carried out in L1 and L2 stage animals. Sample size was 28-187, depending on genotype. Expression of unc47::gfp (otIs39) in PVT is seen only in 15% of post-L3 stage lim-6 ceh-14 animals (n=14), while wild type shows expression in >95% at pre-L3 stages. This stage-dependent downregulation is difficult to interpret, however, because three out of four integrants of the unc47::gfp reporter line juEx60 show no expression in PVT beyond the L3 stage, while only one integrant, otIs39 (tested here), shows expression after the L3 stage. We also noted that in lim-6 ceh-14; otIs39 animals, DVB axon morphology often appears defective.