High Fcp1 phosphatase activity contributes to setting an intense transcription rate required in Drosophila nurse and follicular cells for egg production.

During transcription cycles serine side chains in the carboxyl terminal domain (CTD) of the largest subunit of RNA polymerase II undergo dynamic phosphorylation-de-phosphorylation changes, and the modification status of the CTD serves as a signal for proteins involved in transcription and RNA maturation. We show here that the major CTD de-phosphorylating enzyme Fcp1 is expressed at high levels in germline cells of Drosophila. We used transgene constructs to modify the Fcp1 phosphatase level in Drosophila ovaries and found that high levels of Fcp1 are required for intensive gene expression in nurse cells. On the contrary, low Fcp1 levels might limit the rate of transcription. Fcp1 over-expression results in increased expression of microtubules in nurse cells. Our results show that tightly controlled high level Fcp1 expression in the nurse cells of Drosophila ovaries is required for proper egg maturation.