The Role Of Foxg1 Overexpression In The Pathogenesis Of Severe, Macrocephalic Autism Spectrum Disorder

ASD is as a pervasive neurodevelopmental disorder defined by impairments in social functioning and restricted, repetitive patterns of thought and movement. It has a large genetic component, some of which can be explored using human iPSC-derived organoids, three-dimensional aggregates of iPSC-derived neuronal lineage cells capable of recapitulating aspects of human forebrain development and so modeling the molecular profiles of the developing ASD forebrain. A recent publication from our group, for example, used forebrain organoids to highlight a number of differences between proband ASD-derived organoids and organoids derived from their unaffected fathers, namely that ASD-derived organoids contained more GABAergic neurons and displayed cell cycle shortening; RNA-sequencing (RNA-seq) from these ASD-derived organoids revealed gene expression network disturbances, and in particular highlighted ASD-associated overexpression of FOXG1, a prominent transcription factor in the developing forebrain. shRNA knockdown of FOXG1 rescued this ASD-associated organoid phenotype, suggesting FOXG1 was necessary for ASD organoid phenotype. Here we explored whether this FOXG1 overexpression might also be sufficient to create the ASD organoid phenotype. We created transgenic iPSC lines from probands\u27 unaffected fathers which successfully overexpressed FOXG1. By two separate transgenic methods, however, we unexpectedly observed that FOXG1 overexpression in organoids differentiated from these iPSC lines was much more modest. This disparity between iPSC and organoid FOXG1 overexpression raises interesting questions concerning the transcriptional and epigenetic state of the FOXG1 locus during development and motivates further ongoing epigenetic (including chromatin immunoprecipitation) experiments on these organoids