FOXG1 syndrome is an autism spectrum disorder characterised by a complex group of features, including severe microcephaly, mental retardation, deficient social interactions, poor sleep patterns and irritability.
The syndrome is caused by mutations in FOXG1, a gene which encodes a transcription factor which acts as a high-level regulator of embryonic forebrain development in both humans and mice. In mice, Foxg1 is expressed throughout the embryonic forebrain from very early stages, and mutants that lack Foxg1 die around the time of birth with multiple forebrain defects, the most striking of which is a massive reduction in forebrain size. Foxg1 is very highly conserved between mice and humans and the similarity in phenotypes of mice and humans with Foxg1/FOXG1 mutations strongly suggests that important aspects of the gene’s function are conserved.
Significant numbers of FOXG1 mutations have been described in human patients, including some from the Deciphering Developmental Disorders study co-ordinated by David Fitzpatrick. The project will involve screening existing databases of patient DNA sequences to identify interesting FOXG1 mutations for further exploration, then using CRISPR/Cas9 to introduce mutations found in FOXG1 syndrome patients into the Foxg1 locus in mouse ES cells. These ES cells will be used to grow cerebral organoids – 3D tissue structures grown in vitro, that closely resemble embryonic forebrain. Cerebral organoids offer great potential as tools to investigate brain development, to explore the functions of regulatory genes and to help us understand the root causes of neurodevelopmental disorders. Mouse ES cells will be used in the first instance as mouse organoids develop more quickly and reproducibly than human. The effects of the patient-specific mutations on cellular behaviours such as proliferation, differentiation, migration, and cell death will be measured and attempts made to correlate specific types of defect with mutations in particular domains of the Foxg1 protein.
The phenotypic consequences of loss of Foxg1 are well described, but we know much less about the molecular mechanisms of Foxg1’s action. In an ongoing project in our lab, we have identified a large number of potential downstream target genes, whose expression is altered in Foxg1 mutants, and that have Foxg1 protein bound to their promoter or enhancer regions in neural stem cells. Interesting candidate genes, such as cell cycle regulators, or genes that promote neural differentiation can be identified from this list and tested for their involvement in Foxg1 phenotypes and interactions with Foxg1. In the first instance this would be done in mouse organoids, then testing the strongest candidates in human stem cell derived organoids.
Dr John Mason
Prof David Price
Prof David Fitzpatrick