Disrupted transcriptional networks regulated by CHD1L during neurodevelopment underlie the mirrored neuroanatomical and growth phenotypes of the 1q21.1 copy number variant.

Distal 1q21.1 deletions and duplications are associated with variable phenotypes including autism, head circumference and height defects. To elucidate which gene(s) are responsible for the 1q21.1 duplication/deletion-associated phenotypes, we performed gene manipulation in zebrafish and mice. We modeled 1q21.1 duplication by overexpressing the eight human protein-coding genes in zebrafish. We found that only overexpression of CHD1L led to macrocephaly and increased larval body length, whereas chd1l deletion caused opposite phenotypes. These mirrored phenotypes were also observed in mouse embryos. Transcriptomic, cistromic, and chromatin accessibility analyses of CHD1L knock-out hiPSC-derived neuronal progenitor cells revealed that CHD1L regulates the expression levels and chromatin accessibility of genes involved in neuronal differentiation and synaptogenesis, including autism genes. Moreover, we found that CHD1L favors telencephalon development during forebrain regionalization by facilitating chromatin accessibility to pioneer transcription factors, including SOX2 and OTX2, while simultaneously compacting chromatin through its interaction with the repressor NuRD complex. Overall, our data reveal a novel role for CHD1L as a master regulator of cell fate and its dosage imbalance contributes to the neuroanatomical and growth phenotypes associated with the 1q21.1 distal CNV.