The developmental dynamics of 21U-RNA expression were examined by northern blot analysis using a probe specific for 21U-RNA-3442. 21U-RNA-3442 was expressed at low levels from the L1 to L3 stage, began to accumulate to high levels during the L4 stage, and reached maximal expression in the young adult and gravid adult stages. This pattern of expression correlated with the proliferation of the germline and was consistent with a germline origin. Both RNAs were expressed at approximately equal levels in male- or female-enriched populations but were absent in RNA samples prepared from germline-deficient
glp-4(
bn2) and
eft-3(
q145) mutant populations. Finally, 21UR-3442 was present in embryos, which may reflect maternal and/or paternal loading.