Stalled replication forks within heterochromatin require ATRX for protection

Area of Science:

• Neuroscience
• Genetics
• Cell Biology

Background:

• Neural progenitor cell (NPC) proliferation is crucial for neocortex development and genome integrity.
• Mutations in chromatin regulators, including ATRX, cause developmental disorders like ATRX syndrome, characterized by intellectual disability.

Purpose of the Study:

• To investigate the role of ATRX in maintaining genome integrity during neurogenesis and its link to ATRX syndrome pathogenesis.
• To understand how ATRX deficiency impacts DNA damage response and replication fork stability.

Main Methods:

• Generated forebrain-specific conditional knockout mice lacking the Atrx gene.
• Utilized cell culture models (ATRX-null HeLa cells) and treated them with hydroxyurea to induce replication stress.
• Performed DNA damage assays, measured poly(ADP-ribose) polymerase-1 (Parp-1) and Atm activation, assessed DNA repair protein colocalization (BRCA1-RAD51), and conducted DNA fiber assays.

Main Results:

• Atrx knockout mice exhibited Parp-1 hyperactivation, reduced late-born neurons, and decreased cortical size.
• Progenitor cells showed elevated DNA damage, Parp-1 and Atm activation, leading to increased cell death.
• ATRX-null cells displayed sensitivity to replication stress, DNA damage accumulation, poor proliferation, and impaired replication fork protection.

Conclusions:

• ATRX is essential for limiting replication stress during cellular proliferation.
• PARP-1 activation acts as a compensatory mechanism to protect stalled replication forks in ATRX-deficient cells.
• These findings elucidate ATRX's role in genome maintenance and provide insights into ATRX syndrome.