Figure 4.

Germline VAB-1 function is necessary and sufficient to support normal levels of germ-cell death. (a) Germ-cell corpse counts in ced-10(RNAi) engulfment-defective animals carrying a transgene that directs the expression of VAB-1 under the control of the germline-specific promoter pie-1 (P_pie−1∷vab-1). Germline expression of P_pie−1∷vab-1 rescues the apoptosis deficit in vab-1(dx31) mutants (n: wild type, 21; tnIs13, 19; vab-1, 29; vab-1; tnIs13, 12; Student's t-test, ^*P<0.001). (b) Cell corpse counts in the germline of ced-6(n1823) engulfment-defective animals subjected to RNAi knockdown of endogenous vab-1. Attenuated vab-1 activity by RNAi recapitulates the cell death phenotype of genetic vab-1 mutants in wild-type animals (n: empty vector, 39; vab-1(RNAi), 44) as well as in rrf-1(pk1417) mutant animals that retain RNAi activity in the germline, but lack it in the soma (n: empty vector, 24; vab-1(RNAi), 31; Student's t-test, ^*P<0.001). Cell death is unaffected in ppw-1 mutant animals in which RNAi knockdown functions only in the soma (vab-1 expression is retained in the germline; n: empty vector, 31; vab-1(RNAi), 31). (c) Cell corpse counts in efn-1,2,3 triple mutants (normal engulfment) carrying transgenes that direct heterologous expression of efn-3 cDNA. Expression of efn-3 in the gonad sheath cells (P_lim−7∷efn-3), but not the germline (P_pie−1∷efn-3), partially rescued the germ-cell death defect in the efn triple mutant animals (n=35; Mann–Whitney test with ties adjustment, ^*P=0.001). All graphs summarize data from at least three independent experiments and represent the mean±S.E.M.