The catalytic-dead Pcif1 regulates gene expression and fertility inDrosophila

Abstract

Eukaryotic mRNAs are modified at the 5′ end with a methylated guanosine (m7G) that is attached to the transcription start site (TSS) nucleotide. The TSS nucleotide is 2′-O-methylated (Nm) by CMTR1 in organisms ranging from insects to human. In mammals, the TSS adenosine can be furtherN6-methylated by RNA polymerase II phosphorylated CTD-interacting factor 1 (PCIF1) to create m6Am. Curiously, the fly ortholog of mammalian PCIF1 is demonstrated to be catalytic-dead, and its functions are not known. Here, we show thatPcif1mutant flies display a reduced fertility which is particularly marked in females. Deep sequencing analysis ofPcif1mutant ovaries revealed transcriptome changes with a notable increase in expression of genes belonging to the mitochondrial ATP synthetase complex. Furthermore, the Pcif1 protein is distributed along euchromatic regions of polytene chromosomes, and thePcif1mutation behaved as a modifier of position-effect-variegation (PEV) suppressing the heterochromatin-dependent silencing of thewhitegene. Similar or stronger changes in the transcriptome and PEV phenotype were observed in flies that expressed a cytosolic version of Pcif1. These results point to a nuclear cotranscriptional gene regulatory role for the catalytic-dead fly Pcif1 that is probably based on its conserved ability to interact with the RNA polymerase II carboxy-terminal domain.