Phosphorylation of RNA polymerase II is independent of P-TEFb in the C. elegans germline.

RNA polymerase II (Pol II) elongation in metazoans is thought to require phosphorylation of serine 2 (Ser2-P) of the Pol II C-terminal domain (CTD) by the P-TEFb complex, CDK-9/cyclin T. Another Ser2 kinase complex, CDK-12/cyclin K, which requires upstream CDK-9 activity has been identified in Drosophila and human cells. We show that regulation of Ser2-P in C. elegans soma is similar to other metazoan systems, but Ser2-P in the germline is independent of CDK-9, and largely requires only CDK-12. The observed differences are not due to differential tissue expression as both kinases and their cyclin partners are ubiquitously expressed. Surprisingly, loss of CDK-9 from germ cells has little effect on Ser2-P, yet CDK-9 is essential for germline development. By contrast, loss of CDK-12 and Ser2-P specifically from germ cells has little impact on germline development or function, although significant loss of co-transcriptional H3K36 trimethylation is observed. These results show a reduced requirement for Pol II Ser2-P in germline development and suggest that generating Ser2-P is not the essential role of CDK-9 in these cells. Transcriptional elongation in the C. elegans germline thus appears to be uniquely regulated, which may be a novel facet of germline identity.