Role of AGO2 in Transcriptional Silencing of Spermatogenesis Genes in Drosophila

NAZER EZEQUIEL; LEI, ELISSA P

Seminario; Special session at Drosophila Neuroscience Colloquium; 2015

Argonauteproteins are commonly known as core components of RNA silencing pathways.However, recent work has shown that Argonaute proteins also possess otherfunctions, such as regulation of transcription, splicing and chromatinarchitecture. In particular, Drosophila Argonaute2 (AGO2) has been shownto exhibit substantial genome-wide colocalization with the chromatin insulatorproteins CTCF and CP190. Insulatorproteins possess the ability to mediate inter- and intra-chromosomalinteractions, thus connecting distant regulatory elements in the genome. Forexample, looping between insulator sites could bring an enhancer in proximity toa promoter, thus activating transcription of a gene. Recently, our lab providedthe first evidence for an Argonaute protein functioning directly on euchromatinand affecting enhancer-promoter interaction at the homeotic AbdB-locus independently of the RNAinterference (RNAi) pathway. These results raise the interesting possibilitythat AGO2 could modulate global chromatin architecture, which in turn affectstranscription regulation. To test this hypothesis, Ifirst compared mRNA-Seq libraries from null (AGO2[51B]) and RNA slicingactivity (AGO2[V966M]) AGO2 mutants.Our preliminary data suggest that the absence of AGO2 de-repressestranscription of spermatogenesis genes specifically in females. In this regard,I validated that AGO2 knockdown also promotes up-regulation of spermatogenesisgenes in embryonic and larval female cell lines. In addition, one of the genesde-repressed is nht, aspermatogenesis transcription factor. Interestingly, the nht null mutant suppresses the up-regulation of spermatogenesis genesobserved in AGO2[51B] females, thus suggesting a hierarchical role of AGO2 overnht to silence a spermatogenesis geneprogram. Overall, these results raise the interesting possibility that AGO2 isinvolved in transcriptional silencing of a testis-specific gene expression programthroughout female development, thus contributing to proper sexual dimorphism.