Altered Neocortical Gene Expression, Brain Overgrowth and Functional Over-Connectivity in Chd8 Haploinsufficient Mice.

Iván Crespo-Enríquez ,M Albert Basson ,Robert Ellingford,Cathy Fernandes,Conor Mohan,María Luisa Scattoni ,Philipp Suetterlin,Alessio Delogu,Shaun Hurley,Kimberley L H Riegman ,Philippa Francis‐West ,Yohan Yee,Angela Caruso,Olivier Brock,Maria Pia Pagani ,Jacob Ellegood,Alberto Galbusera,Jason P Lerch ,Caterina Michetti,Alessandro Gozzi

doi:10.1093/cercor/bhy058

Abstract

Truncating CHD8 mutations are amongst the highest confidence risk factors for autism spectrum disorder (ASD) identified to date. Here, we report that Chd8 heterozygous mice display increased brain size, motor delay, hypertelorism, pronounced hypoactivity, and anomalous responses to social stimuli. Whereas gene expression in the neocortex is only mildly affected at midgestation, over 600 genes are differentially expressed in the early postnatal neocortex. Genes involved in cell adhesion and axon guidance are particularly prominent amongst the downregulated transcripts. Resting-state functional MRI identified increased synchronized activity in cortico-hippocampal and auditory-parietal networks in Chd8 heterozygous mutant mice, implicating altered connectivity as a potential mechanism underlying the behavioral phenotypes. Together, these data suggest that altered brain growth and diminished expression of important neurodevelopmental genes that regulate long-range brain wiring are followed by distinctive anomalies in functional brain connectivity in Chd8+/− mice. Human imaging studies have reported altered functional connectivity in ASD patients, with long-range under-connectivity seemingly more frequent. Our data suggest that CHD8 haploinsufficiency represents a specific subtype of ASD where neuropsychiatric symptoms are underpinned by long-range over-connectivity.

Highlights

Autism spectrum disorder (ASD) is diagnosed on the basis of socio-communicative deficits and repetitive, perseverative behaviors with restricted interests (APA 2013)
Quantitative RT-PCR on RNA isolated from E12.5 and P5 neocortices using primers spanning the exon 3/4 boundary showed Chd8 expression reduced by 64% (P = 0.006) and 52% (P = 0.01), respectively (Supplementary Fig. S1D)
We found no evidence for a truncated protein product of 419aa (∼45 kDa) that may have resulted from translation of any mutant transcript (Supplementary Fig. S1E). Quantitative RT-PCR (qRT-PCR) analysis at E12.5 with primers spanning the exon 1/2 boundary revealed reduced Chd8 expression of 52% (Supplementary Fig. S1G), indicating that the mutant transcript is most likely subject to nonsense-mediated decay

Summary

Introduction

Autism spectrum disorder (ASD) is diagnosed on the basis of socio-communicative deficits and repetitive, perseverative behaviors with restricted interests (APA 2013). The phenotypic and genetic heterogeneity of ASD has hampered the elucidation of the molecular mechanisms that may underlie specific behavioral symptoms. The recent identification of de novo, likely gene disrupting (LGD) mutations that show highly significant associations with autism (Neale et al 2012; Talkowski et al 2012; O’Roak et al 2012b; Iossifov et al 2014; O’Roak et al 2014) provides an opportunity to phenotype and molecularly characterize genetically defined ASD subtypes. Exome sequencing studies of several thousand simplex families detected de novo, LGD mutations in the CHD8 (Chromodomain Helicase DNA binding factor 8) gene (Neale et al 2012; Talkowski et al 2012; O’Roak et al 2012b; Iossifov et al 2014; O’Roak et al 2014). The recruitment of CHD8 to gene promoters in mouse and human neural progenitors is strongly associated with transcriptional activation, while CHD8 knock-down in these cells results in the reduced expression of many ASD-associated genes (Sugathan et al 2014; Cotney et al 2015)

Methods

Results

Conclusion