ATRX histone binding and helicase activities have distinct roles in neuronal differentiation

Abstract

ATRX is a chromatin remodeler, which is mutated in ATRX syndrome, a neurodevelopmental disorder. ATRX mutations that alter histone binding or chromatin remodeling activities cluster in the PHD finger or the helicase domain respectively. Using engineered mouse embryonic stem cells that exclusively express ATRX protein with mutations in the PHD finger (PHDmut) or helicase domains (K1584R), we examine how specific ATRX mutations affect neurodifferentiation. ATRX PHDmut and K1584R proteins interact with the DAXX histone chaperone but show reduced localization to pericentromeres. Neurodifferentiation is both delayed and compromised in PHDmut and K1584R, and manifest differently from complete ATRX loss. We observe reduced enrichment of PHDmut protein to ATRX targets, while K1584R accumulates at these sites. Interestingly, ATRX mutations have distinct effects on the genome-wide localization of the polycomb repressive complex 2 (PRC2), with PHDmut and ATRX knockout showing reduced PRC2 binding at polycomb targets and K1584R showing loss at some sites and gains at others. Notably, each mutation associated with unique gene signatures, suggesting distinct pathways leading to impaired neurodifferentiation. Our results indicate that the histone binding and chromatin remodeling functions of ATRX play non-redundant roles in neurodevelopment, and when mutated lead to ATRX syndrome through separate regulatory pathways.

A new mouse model of ATR-X syndrome carrying a common patient mutation exhibits neurological and morphological defects

“…We found that ATRX[R245C] mutant protein is sufficient to rescue the neuronal death phenotype present in mice lacking ATRX in the forebrain. This is supported by a recent study using CRISPR-edited mouse ESC-derived neural progenitor cells (NPCs) where a cell death phenotype was observed in cells lacking ATRX, but not in those expressing a stable mutant ATRX with two amino acid changes in the ADD domain that specifically abolish heterochromatin binding (Bieluszewska et al, 2022). This raises the question of whether mutating the ADD domain can cause elevated replicative stress, as has been described in Atrx-null NPCs (Watson et al, 2013) and myoblasts (Huh et al, 2012).…”

The Chromatin Remodeler ATRX: Role and Mechanism in Biology and Cancer

“…Numerous SNF2 proteins utilize the energy released by ATP hydrolysis to translocate along DNA, therefore remodeling DNA structures or DNA-protein interactions, as well as ATRX. ATRX’s histone-binding and chromatin-remodeling capabilities play a unique role in neuronal differentiation [ 26 ]. Mutations in the ATRX protein’s PHD finger have diverse effects on the genome-wide location of polycomb repressive complex 2 (PRC2), whereas mutations in the helicase domain induce loss in some places and gains in others.…”