RETROSPLENIAL CORTEX INVOLVEMENT IN NOVELTY EXPLORATION ALTERATIONS IN A MOUSE MODEL OF AUTISM

Altered cortical circuit development has been strongly implicated in autism spectrum disorders (ASD). Pathogenic variants in DDX3X cause DDX3X syndrome, a neurodevelopmental condition frequently co-morbid with ASD. Our laboratory generated the first mouse model with construct and face validity for Ddx3x haploinsufficiency. Female Ddx3x^⁺/⁻ mice exhibit abnormal neocortical development and altered behavior during open field (OF) exploration; however, the cellular and circuit mechanisms linking these phenotypes remain poorly defined.
To bridge this gap, we mapped whole-brain neuronal activity in Ddx3x^⁺/⁻ and control female mice following OF exploration using iDISCO+ tissue clearing combined with Fos immunolabeling and light-sheet microscopy. Ddx3x^⁺/⁻ mice display a distinct experience-dependent activation pattern, revealing differentially engaged brain regions. Notably, enhanced activation was observed across cortical areas, including the retrosplenial cortex (RSP), a region critical for spatial information processing and priorly linked to ASD deficits.
To establish causal and regional specificity, we controlled RSP activity using chemogenetics via stereotaxic delivery of inhibitory DREADDs and assessed their effects on OF behavior in both genotypes. Additionally, we induced region-specific Ddx3x ablation through stereotaxic injection of a Cre viral vector into the RSP of Ddx3x^flx/+ mice. Both manipulations showed a partial reversion of maladaptive behaviors. Additionally, using a Thy1-GFP reporter line, we examined experience-dependent dendritic spine remodeling and performed transcriptomic analyses to identify molecular signatures altered by Ddx3x haploinsufficiency.
Together, these findings implicate dysregulated RSP circuitry in abnormal spatial exploration in Ddx3x haploinsufficient mice and highlight experience-dependent, malleable circuit and molecular targets relevant to DDX3X syndrome and ASD.