Abstracts

Rationale: De novo mutations in the chromatin remodeler, Chd2, are increasingly linked to early onset epilepsy, Lennox-Gastaut Syndrome, intellectual disability and autism. However, little is known about the role of Chd2 in neural circuit development or function. Here, we generated a new Chd2+/- mouse and evaluated the development of forebrain neurons at different stages of cortical development in these animals. We are also investigating whether Chd2+/- mice develop epilepsy or other epilepsy-related behaviors (e.g., deficits in learning and memory). Methods: We generated a Chd2 floxed transgenic mouse, and crossed these animals with ߭actin-Cre mice (to generate Chd2+/- mice) or Nkx2.1-Cre mice (to generate Chd2+/- only in a subpopulation of GABAergic interneurons). Western blot was used to evaluate Chd2 protein expression in wild-type, Chd2+/- and Chd-/- mice at P30. Immunostaining co-labeling studies were performed to evaluate expression of Chd2 in different brain cell types and to quantify the density of cortical cell types in wild-type and Chd2 mutants. Coronal slices were prepared from P30 wild-type and Chd2 mutant mice, and whole-cell patch-clamp recordings were obtained from layer II/III pyramidal neurons. Spontaneous and miniature, EPSCs and IPSCs were obtained at -70mV and 0mV, respectively. Intrinsic membrane and firing properties were assessed by measuring responses to hyperpolarizing and depolarizing current injections in current-clamp configuration. A series of behavioral assays and long-term video-EEG recording experiments are currently being performed to evaluate epilepsy-related phenotypes in Chd2 mutant mice. Results: Chd2 was expressed in mouse embryonic forebrain as early as embryonic day13.5 and remained highly expressed throughout the brain in adult animals. At P30, Chd2 co-labeling was found in neurons (NeuN), including GABAergic interneurons (GAD67), but absent in putative astrocytes (GFAP) of wild-type animals. Western blot analysis showed a reduction of Chd2 protein in brain of Chd2+/- mice. Immunostaining analysis in somatosensory cortex did not reveal a change in cortical lamination of Chd2+/- mice, but did reveal reduced density of GABAergic interneurons at P30. Patch-clamp recordings obtained from layer II/III pyramidal neurons in somatostensory neocortex revealed increased EPSC frequencies in Chd2+/- mice at P30; intrinsic electrophysiological properties were unchanged. Conclusions: Our findings suggest increased excitatory synaptic input to principal neurons and loss of GABAergic interneurons in Chd2 mutant mice. Cell type-specific impairments in cortical development and function may contribute to behavioral disturbances associated with Chd2 mutation. Funding: LGS Foundation NIH / NINDS R00 NS085046 NIH / NINDS R01 NS096012 NIH / NINDS T32 NS045540