Abstracts

Rationale: Exome sequencing studies have now identified hundreds of gene mutations carrying an increased risk for neurodevelopmental disorders. Of these, mutations in genes encoding chromatin regulators have emerged as a common risk factor, with CHD2, a member of the chromodomain helicase DNA-binding (CHD) family of proteins, being frequently affected. CHD2 is an ATP-dependent chromatin-remodeling factor with poorly understood function in the developing or adult brain. In human, Chd2 haploinsufficiency is associated with intellectual disability, a variety of catastrophic childhood epilepsies, autism spectrum disorder and photosensitivity, with large phenotypic variability among affected individuals. In mice, heterozygous deletion of Chd2 results in histological abnormalities of heart, muscle, lung, liver, kidney, spleen and bone. Initial studies in brain indicate Chd2 knockdown during the peak of embryonic neurogenesis promotes production of neurons from neural progenitors, possibly depleting the precursor pool. However, unlike other CHD family members in which recent progress using animal models has led to important mechanistic insights about behavioral phenotypes and cellular pathways, there is essentially nothing known about brain defects that arise as a consequence of Chd2 haploinsufficiency. Methods: We generated Chd2+/- mice by crossing transgenic mice containing loxP sites flanking exon 3 of Chd2 to a ß-actin Cre line. Wild-type and Chd2+/- littermates were evaluated in a series of immunostaining experiments at E14.5, P7 and P30. Whole-cell patch-clamp recordings and long-term EEG monitoring experiments were performed in young-adult animals at P30-P65. Long-term memory assays were performed at P60. Differentially expressed genes between WT and Chd2 mutant mice were examined by RNA-sequencing on E13.5 MGE, E13.5 cortex, and P45 hippocampus.  Results: We report mice with heterozygous mutations in Chd2 exhibit deficits in neuronal proliferation and a shift in neuronal excitability that included divergent changes in excitatory and inhibitory synaptic function. Further in vivo experiments show Chd2^+/- mice displayed aberrant cortical rhythmogenesis and severe deficits in long-term memory, consistent with phenotypes observed in humans. We identified broad, age-dependent transcriptional changes in Chd2^+/- mice, including alterations in neurogenesis, synaptic transmission and disease-related genes. We replicated our results in a second, independent cohort of mice with Chd2 haploinsufficiency only in inhibitory interneurons and are now evaluating interneuron-based rescue experiments designed specifically for Chd2^+/-. Conclusions: Our results demonstrate a critical role for Chd2 in neurodevelopment and provide initial insight into how Chd2 haploinsufficiency leads to aberrant cortical network function and impaired memory. Funding: Lennox-Gastaut Syndrome FoundationNINDS R01-NS096012NINDS R00-NS085046NINDS T32-NS045540NINDS T32-NS082174