# PARG Mutation Uncovers Critical Structural Determinant for Poly(ADP-Ribose) Hydrolysis and Chromatin Regulation in Embryonic Stem Cells

## TL;DR

This study identifies a key structural part of PARG needed for breaking down poly(ADP-ribose), showing its role in embryonic stem cells and development.

## Contribution

A novel Parg29b mutant mouse ESC line reveals a critical structural determinant of PARG function in pADPr hydrolysis.

## Key findings

- A PARG catalytic domain deletion abolishes pADPr hydrolysis but does not affect ESC viability or proliferation.
- The mutation disrupts the pADPr pathway in Drosophila, halting developmental progression.
- The study provides a genetically tractable model for studying pADPr dynamics and PARP inhibition responses.

## Abstract

Poly(ADP-ribosyl)ation is a crucial posttranslational modification that governs gene expression, chromatin remodeling, and cellular homeostasis. This dynamic process is mediated by the opposing activities of poly(ADP-ribose) polymerases (PARPs), which synthesize poly(ADP-ribose) (pADPr), and poly(ADP-ribose) glycohydrolase (PARG), which degrades it. While PARP function has been extensively studied, the structural and mechanistic basis of PARG-mediated pADPr degradation remain incompletely understood. To investigate the role of PARG in pADPr metabolism, we employed CRISPR/Cas9-based genome editing to generate a novel Parg29b mutant mouse embryonic stem cell (ESC) line carrying a precise deletion within the PARG catalytic domain. This deletion completely abolished pADPr hydrolytic activity, resulting in massive nuclear pADPr accumulation, yet ESC viability, proliferation, and cell cycle progression remained unaffected. Using Drosophila melanogaster as a model system, we demonstrated that this mutation completely disrupted the pADPr pathway and halted developmental progression, highlighting the essential role of PARG and pADPr turnover in organismal development. Our results define a critical structural determinant of PARG catalytic function, underscore the distinct requirements for pADPr metabolism in cellular versus developmental contexts, and provide a genetically tractable model for studying the regulation of poly(ADP-ribose) dynamics and therapeutic responses to PARP inhibition in vivo.