FOXG1 is an ancient transcription factor gene mastering telencephalic development. A number of distinct structural FOXG1 mutations lead to the “FOXG1 syndrome”, a complex and heterogeneous neuropathological entity, for which no cure is presently available. Reconstruction of primary neurodevelopmental/physiological anomalies evoked by these mutations is an obvious pre-requisite for future, precision therapy of such syndrome. Here, as a proof-of-principle, we functionally scored three FOXG1 neuropathogenic alleles, FOXG1G224S, FOXG1W308X, and FOXG1N232S, against their healthy counterpart. Specifically, we delivered transgenes encoding for them to dedicated preparations of murine pallial precursors and quantified their impact on selected neurodevelopmental and physiological processes mastered by Foxg1: pallial stem cell fate choice, proliferation of neural committed progenitors, neuronal architecture, neuronal activity, and their molecular correlates. Briefly, we found that FOXG1G224S and FOXG1W308X generally performed as a gain- and a loss-of-function-allele, respectively, while FOXG1N232S acted as a mild loss-of-function-allele or phenocopied FOXG1WT. These results provide valuable hints about processes misregulated in patients heterozygous for these mutations, to be re-addressed more stringently in patient iPSC-derivative neuro-organoids. Moreover, they suggest that murine pallial cultures may be employed for fast multidimensional profiling of novel, human neuropathogenic FOXG1 alleles, namely a step propedeutic to timely delivery of therapeutic precision treatments.

This protocol aims at standardizing the procedure to obtain primary cultures of hippocampal and cerebrocortical neurons for in vitro experiments. Cultures should be prepared from cells isolated during embryonic development when neuronal precursor cells are not yet fully differentiated. This helps increasing the quality and quantity of cells, while offering minimal cell death that often occurs during dissociation of differentiated neurons. Cells plated under the appropriate conditions, either in Petridishes or in multi-well plates, will develop and establish synaptic contacts over time since the neuronal culture medium provides the nutrients and trophic factors required for differentiation. In this protocol we describe the methodology for the preparation of both cortical and hippocampal neuronal cultures.