The PIWI-interacting RNA (piRNA) pathway controls transposon expression in animal germ cells, thereby ensuring genome stability over generations. In Drosophila, piRNAs are intergenerationally inherited through the maternal lineage, and this has demonstrated importance in the specification of piRNA source loci and in silencing of I- and P-elements in the germ cells of daughters. Maternally inherited Piwi protein enters somatic nuclei in early embryos prior to zygotic genome activation and persists therein for roughly half of the time required to complete embryonic development. To investigate the role of the piRNA pathway in the embryonic soma, we created a conditionally unstable Piwi protein. This enabled maternally deposited Piwi to be cleared from newly laid embryos within 30 minutes and well ahead of the activation of zygotic transcription. Examination of RNA and protein profiles over time, and correlation with patterns of H3K9me3 deposition, suggests a role for maternally deposited Piwi in attenuating zygotic transposon expression in somatic cells of the developing embryo. In particular, robust deposition of piRNAs targeting roo, an element whose expression is mainly restricted to embryonic development, results in the deposition of transient heterochromatic marks at active roo insertions. We hypothesize that roo, an extremely successful mobile element, may have adopted a lifestyle of expression in the embryonic soma to evade silencing in germ cells.
Raw data from high-throughput sequencing experiments are available at GEO under accession number GSE160778. Raw data from proteomics experiments are available on PRIDE with accession number PXD0022409. Source data files have been provided for Figures 1 and 2.
Maternally inherited piRNAs silence transposons during Drosophila embryogenesisNCBI Gene Expression Omnibus, GSE160778.
Maternally inherited piRNAs silence transposons during Drosophila embryogenesisPRIDE Archive, PXD0022409.
piRNA-guided co-transcriptional silencing coopts nuclear export factorsNCBI Gene Expression Omnibus, GSE121661.
- Gregory J Hannon
- Gregory J Hannon
- Gregory J Hannon
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
© 2021, Fabry et al.
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