Regulation of the Drosophila transcriptome by Pumilio and the CCR4-NOT deadenylase complex

The sequence-specific RNA-binding protein Pumilio controls Drosophila development; however, the network of mRNAs that it regulates remains incompletely characterized. In this study, we utilize knockdown and knockout approaches coupled with RNA-Seq to measure the impact of Pumilio on the transcriptome of Drosophila cells in culture. We also use an improved RNA co-immunoprecipitation method to identify Pumilio-bound mRNAs in Drosophila embryos. Integration of these datasets with the locations of Pumilio binding motifs across the transcriptome reveal novel direct Pumilio target genes involved in neural, muscle, wing, and germ cell development, and cellular proliferation. These genes include components of Wnt, TGF-beta, MAPK/ERK, and Notch signaling pathways, DNA replication, and lipid metabolism. We identify the mRNAs regulated by the CCR4-NOT deadenylase complex, a key factor in Pumilio-mediated repression, and observe concordant regulation of Pumilio:CCR4-NOT target mRNAs. Computational modeling reveals that Pumilio binding, binding site number, clustering, and sequence context are important determinants of regulation. In contrast, we show that the responses of direct mRNA targets to Pumilio-mediated repression are not influenced by their content of optimal synonymous codons. Moreover, contrary to a prevailing model, we do not detect a role for CCR4-NOT in the degradation of mRNAs with low codon optimality. Together, the results of this work provide new insights into the Pumilio regulatory network and mechanisms, and the parameters that influence the efficacy of Pumilio-mediated regulation.