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Updated: Dec 23, 2025
A Non-random Mouse Model for Pharmacological Reactivation of Mecp2 on the Inactive X Chromosome
Published on: May 22, 2019
Suppressor mutations in Mecp2-null mice implicate the DNA damage response in Rett syndrome pathology
Adebola Enikanolaiye1, Julie Ruston1, Rong Zeng1
1Program in Genetics and Genome Biology, The Hospital for Sick Children, Toronto, Ontario, M5G 0A4, Canada.
Abstract:
Mutations in X-linked methyl-CpG-binding protein 2 (MECP2) cause Rett syndrome (RTT). To identify functional pathways that could inform therapeutic entry points, we carried out a genetic screen for secondary mutations that improved phenotypes in Mecp2/Y mice after mutagenesis with N-ethyl-N-nitrosourea (ENU). Here, we report the isolation of 106 founder animals that show suppression of Mecp2-null traits from screening 3177 Mecp2/Y genomes. Whole-exome sequencing, genetic crosses, and association analysis identified 22 candidate genes. Additional lesions in these candidate genes or pathway components associate variant alleles with phenotypic improvement in 30 lines. A network analysis shows that 63% of the genes cluster into the functional categories of transcriptional repression, chromatin modification, or DNA repair, delineating a pathway relationship with MECP2. Many mutations lie in genes that modulate synaptic signaling or lipid homeostasis. Mutations in genes that function in the DNA damage response (DDR) also improve phenotypes in Mecp2/Y mice. Association analysis was successful in resolving combinatorial effects of multiple loci. One line, which carries a suppressor mutation in a gene required for cholesterol synthesis, Sqle, carries a second mutation in retinoblastoma binding protein 8, endonuclease (Rbbp8, also known as CtIP), which regulates a DDR choice in double-stranded break (DSB) repair. Cells from Mecp2/Y mice have increased DSBs, so this finding suggests that the balance between homology-directed repair and nonhomologous end joining is important for neuronal cells. In this and other lines, two suppressor mutations confer greater improvement than one alone, suggesting that combination therapies could be effective in RTT.
Insights
Researchers identified secondary mutations that suppress Rett syndrome (RTT) symptoms in Mecp2-null mice. These findings highlight pathways involving DNA repair and chromatin modification, suggesting potential combination therapies for RTT.
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.
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