# PNUTS:PP1 recruitment to Tox4 regulates chromosomal dispersal in Drosophila germline development

## TL;DR

This study explores how the PNUTS-Tox4-PP1 phosphatase complex regulates chromosome dispersal and gene expression during fruit fly germline development.

## Contribution

The paper reveals the functional roles of Tox4 in PNUTS-dependent and -independent processes during germline development and identifies its zinc-dependent interaction with PNUTS.

## Key findings

- Tox4 is essential for fertility in Drosophila, with roles in germline development both dependent and independent of PNUTS.
- Tox4 binds the PNUTS TND on a distinct surface and requires zinc for this interaction.
- Disruption of PNUTS-Tox4 and PNUTS-PP1 interactions impairs gene expression and chromosomal dispersal during oogenesis.

## Abstract

Ser/Thr protein phosphatase 1 (PP1) forms a large nuclear holoenzyme (with PNUTS, WDR82, and Tox4) whose emerging role is to regulate transcription. However, the role of Tox4, and its interplay with the other phosphatase subunits in this complex, is poorly understood. Here, we combine biochemical, structural, cellular, and in vivo experiments to show that, while tox4 is dispensable for viability, it is essential for fertility, having both PNUTS-dependent and -independent roles in Drosophila germline development. We also show that Tox4 requires zinc for PNUTS TFIIS N-terminal domain (TND) binding, and that it binds the TND on a surface distinct from that used by established TND-interacting transcriptional regulators. We also show that selective disruption of the PNUTS-Tox4 and the PNUTS-PP1 interaction is critical for normal gene expression and chromosomal dispersal during oogenesis. Together, these data demonstrate how interactions within the PNUTS-Tox4-PP1 phosphatase combine to tune transcriptional outputs driving developmental transitions.

Duncalf et al. investigate the evolutionarily conserved interaction between the PNUTS N-terminal domain and the TOX4 C-terminal domain, resolving the PNUTS:TOX4 complex crystal structure. Leveraging these insights, the authors define the functional significance of Tox4-PNUTS-PP1 interactions in Drosophila germline development, highlighting their cooperative role in developmentally controlled chromosome reorganization.