# Loss of CTLH component MAEA impairs DNA repair and replication and leads to developmental delay

## TL;DR

Loss of the MAEA protein impairs DNA repair and replication, leading to developmental delays in patients with MAEA variants.

## Contribution

MAEA is identified as a critical regulator of DNA repair and replication, and its dysfunction is linked to a new developmental disorder called DIADEM.

## Key findings

- MAEA is a core subunit of the CTLH E3 ligase complex and is essential for homologous recombination and replication stress response.
- Eight patients with MAEA variants exhibit global developmental delay and intellectual disability.
- MAEA dysfunction reduces RAD51 loading at DNA damage sites, impairing DNA repair and replication fork progression.

## Abstract

Ubiquitin E3 ligases play crucial roles in the DNA damage response (DDR) by modulating the turnover, localization, activation, and interactions of DDR and DNA replication proteins. We performed a CRISPR-Cas9 knockout screen focused on ubiquitin E3 ligases and related proteins with the DNA topoisomerase I inhibitor camptothecin. This led us to establish that MAEA, a core subunit of the CTLH E3 ligase complex, is a critical regulator of homologous recombination and the replication stress response. In tandem, we identified eight patients with variants in MAEA who present with a neurodevelopmental disorder that we term DIADEM (Developmental delay and Intellectual disability Associated with DEfects in MAEA). Analysis of patient-derived cell lines and mutation modeling reveal an underlying defect in HR-dependent DNA repair and replication fork restart and protection as a likely cause of disease. Mechanistically, we find that MAEA dysfunction hinders DNA repair by reducing the efficiency of RAD51 loading at sites of DNA damage, which we propose may contribute to the presentation of DIADEM by compromising genome integrity and cell division during development.

The E3 ubiquitin ligase subunit MAEA promotes RAD51 loading to drive DNA repair and replication. In its absence, cells struggle to survive replication stress. MAEA variants found in patients presenting with a nonsyndromic developmental disorder called DIADEM also impair DNA repair and replication.

MAEA loss prevents RAD51 loading and, consequently, efficient repair of single-ended double-strand breaks by homologous recombination (HR).MAEA null cells face impaired replication fork progression, protection, and restart, making them vulnerable to replication stress.Eight patients with variants in MAEA present with DIADEM, a condition characterized by global developmental delay.Clinical MAEA variants yield similar sensitivities to DNA damage and replication stress when compared to MAEA null cells.MAEA loss is a putative marker of HR deficiency and could provide a novel axis for therapeutic diagnosis and intervention.

MAEA loss prevents RAD51 loading and, consequently, efficient repair of single-ended double-strand breaks by homologous recombination (HR).

MAEA null cells face impaired replication fork progression, protection, and restart, making them vulnerable to replication stress.

Eight patients with variants in MAEA present with DIADEM, a condition characterized by global developmental delay.

Clinical MAEA variants yield similar sensitivities to DNA damage and replication stress when compared to MAEA null cells.

MAEA loss is a putative marker of HR deficiency and could provide a novel axis for therapeutic diagnosis and intervention.

The E3 ubiquitin ligase subunit MAEA promotes RAD51 loading to drive DNA repair and replication. In its absence, cells struggle to survive replication stress. MAEA variants found in patients presenting with a nonsyndromic developmental disorder called DIADEM also impair DNA repair and replication.