Pol II CTD phosphorylation is uniquely regulated in primordial germ cells (PGCs). (A) H5 staining in ama-1 (RNAi) is depleted by ama-1(RNAi). (B) cdk-9 (RNAi) embryo ablates H5 staining in all cells except the PGCs. (C) tlk-1 (RNAi) ablates H5 staining in many somatic cells, but the PGCs are often resistant. (D) cdk-9; tlk-1(RNAi) consistently ablates all H5 staining, including that in PGCs. Note that polyploid nuclei are observed in the tlk-1 (RNAi) embryo, as described previously . H5 and DAPI staining (middle and right, respectively) are shown in grayscale with the merged image (left). Arrows indicate the PGCs.