Suppressor mutations in Mecp2-null mice implicate the DNA damage response in Rett syndrome pathology

Area of Science:

• Neuroscience
• Genetics
• Molecular Biology

Background:

• Mutations in the methyl-CpG-binding protein 2 (MECP2) gene cause Rett syndrome (RTT), a severe neurodevelopmental disorder.
• Identifying functional pathways affected by MECP2 loss is crucial for developing therapeutic strategies.

Purpose of the Study:

• To conduct a genetic screen for secondary mutations that ameliorate RTT phenotypes in Mecp2-mutant mice.
• To identify genes and pathways that interact with MECP2 and could serve as therapeutic targets.

Main Methods:

• A forward genetic screen using N-ethyl-N-nitrosourea (ENU) mutagenesis in Mecp2/Y mice.
• Whole-exome sequencing, genetic crosses, and association analysis to identify suppressor mutations.
• Network analysis to categorize identified genes by function and pathway involvement.

Main Results:

• Screening 3177 Mecp2/Y genomes identified 106 founder animals with suppressed RTT traits.
• Whole-exome sequencing and genetic analysis pinpointed 22 candidate suppressor genes.
• Network analysis revealed that 63% of identified genes cluster in transcriptional repression, chromatin modification, or DNA repair pathways, highlighting functional links to MECP2.
• Mutations in genes involved in synaptic signaling, lipid homeostasis, and DNA damage response (DDR) were found to suppress Mecp2-null phenotypes.
• Combinatorial effects of multiple suppressor mutations demonstrated enhanced phenotypic improvement, as seen in a line with mutations in cholesterol synthesis (Sqle) and DNA repair (Rbbp8/CtIP).

Conclusions:

• Secondary mutations can effectively suppress Mecp2-null phenotypes, revealing critical pathways interacting with MECP2.
• The DNA damage response (DDR) and its regulation, particularly the balance in double-stranded break (DSB) repair, are important in Mecp2-deficient neuronal cells.
• The findings suggest that combination therapies targeting multiple pathways may offer a more effective treatment strategy for Rett syndrome.