# Understanding the mechanism of Piwi-induced transcriptional silencing

> **NIH NIH R01** · CALIFORNIA INSTITUTE OF TECHNOLOGY · 2021 · $351,750

## Abstract

Project summary
 The piRNA pathway is an evolutionarily conserved mechanism that acts in the germline of metazoans to
repress the activity of transposable elements and ensure genome integrity and fertility. At the core of the pathway
lies an Argonaute protein of the Piwi clade and the associated small non-coding RNA, piwi-interacting (pi)RNA,
which guides the Piwi protein to its targets. In the cytoplasm Piwi proteins act by destroying the mRNA targets
using their intrinsic nuclease activity. piRNA also guide nuclear the Piwi to establish repressive chromatin and
induce transcriptional repression of genomic targets. We have found that SUMO and an E3 SUMO ligase play
an essential role in piRNA-guided transcriptional repression by linking the nuclear Piwi complex to the chromatin
modifier. However, individual steps of piRNA-guided chromatin repression remain poorly understood. In this
proposal, we will investigate the molecular mechanism of piRNA-guided repression. We will determine how the
SUMO ligase is recruited to genomic piRNA targets and explore the role of SUMO in assembly of the repressive
piRNA complexes.
 We will determine functions of Piwi and piRNA in establishment of repressive chromatin and initiation of piRNA
biogenesis. In addition to its function in the germline of adult flies, the maternal Piwi-piRNA complex is deposited
into the egg and was proposed to activate piRNA biogenesis in the progeny. However, Piwi is indispensable for
oogenesis preventing direct interrogation of its embryonic function. To circumvent this problem and study the
function of maternal Piwi in embryogenesis we have developed a strategy for depleting maternal Piwi in the
embryo. We will apply this strategy to probe the role of Piwi in specification of piRNA clusters in primordial germ
cells. How distinct chromatin domains are demarcated is the central question of chromatin biology. In animals,
heterochromatin is disassembled in gametes and re-established during embryogenesis. How heterochromatin
is assembled de novo during development remains poorly understood. Transposable elements comprise the
bulk of heterochromatin, making Piwi-piRNA complexes an ideal tool for finding and marking heterochromatin
sequences. During early zygotic development maternal Piwi-piRNA complexes are localized to somatic nuclei of
the embryo. We propose that Piwi-bound piRNAs direct de novo establishment of repressive chromatin domains
in somatic cells of the early embryo followed by its piRNA-independent propagation and maintenance during
later development. We will explore this model by depleting maternal Piwi and analyzing its effect on chromatin.
 The proposed work will advance our knowledge of RNA-mediated regulation and of transcription chromatin
structure in animals. We explore the function of piRNA in transmission of epigenetic information from generation
to generation. Our studies promise to shed new light on how distinct chromatin domains are demarked. A detailed
mechanistic...

## Key facts

- **NIH application ID:** 10122720
- **Project number:** 2R01GM110217-06A1
- **Recipient organization:** CALIFORNIA INSTITUTE OF TECHNOLOGY
- **Principal Investigator:** Katalin Fejes Toth
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $351,750
- **Award type:** 2
- **Project period:** 2014-08-01 → 2025-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10122720

## Citation

> US National Institutes of Health, RePORTER application 10122720, Understanding the mechanism of Piwi-induced transcriptional silencing (2R01GM110217-06A1). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10122720. Licensed CC0.

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