C. elegans has seven genes coding for proteins homologous to the members of the serine protease family S9, which includes dipeptidyl peptidase IV (DPPIV)/CD26 and seprase/fibroblast activation protein (FAP), which have been reported to participate in cell migration in mammals, but the details of their functions are not well known. In this study, double RNAi analysis was performed on six of the family S9 genes,
dpf-1~
dpf-6, and it was found that inhibition of DPF activities causes abnormal distal tip cell (DTC) migration. Interestingly, double RNAi caused abnormal DTC migration in any combination of family members, while no single RNAi caused the abnormality. The effect of RNAi was most prominent when
dpf-1 and
dpf-2 were interfered simultaneously. Similar results were obtained by using deletion mutants. By in situ hybridization and immunostaining of the dpf gene products, the mRNA and proteins were all detected in the DTCs at the L1 and L2 stages. By real time PCR and Western blot analysis, we found an increase of the
try-1 mRNA and protein in each dpf-knock out animals at the L3 and L4 stages. TRY-1 is a member of trypsin-type serine proteases. RNAi of
try-1 showed no abnormality on its own, while double RNAi of
try-1 and one of the dpf genes caused abnormal gonad morphogenesis. In addition, we found that the amount of dpf gene products increases in the
gon-1(RNAi) animals at the L1-L2 stages, and that double RNAi of two dpf genes suppressed the
gon-1(RNAi) phenotype (failure of gonad elongation). In the
gon-1(RNAi)
dpf-1(RNAi)
dpf-2(RNAi) animals, many gonad arms were elongated. A similar result was also obtained with the
gon-1(RNAi)
dpf-1(RNAi)
try-1(RNAi) animals. Because the abnormal DTC structure in
gon-1 (RNAi) animals was reported by Blelloch et al. (Dev. Biol. 216:382-93, 1999), we observed the DTCs of the
gon-1(RNAi) animals in detail by electron microscopy and found abnormal membrane-like structures, which disappeared by double RNAi of the dpf genes. Then we investigated which organelles had been influenced by
gon-1(RNAi). As a result, when endoplasmic reticulum was labeled with C31E10.7::venus under the control of the
lag-2 promoter, the fluorescence pattern was changed, which was suppressed by additional RNAi of
dpf-1 and
dpf-2.