A UNIFYING FRAMEWORK TO STUDY THE GENETIC AND ENVIRONMENTAL FACTORS SHAPING HUMAN BRAIN DEVELOPMENT

The development of human brain is a fascinating and complex process that still needs to be uncovered at the molecular resolution. Even though animal studies have revealed a lot of its unfolding, the fine regulation of cellular differentiation trajectories that characterizes humans has become only recently open to experimental tractability, thanks to the development of organoids, human cellular models that are able to recapitulate the spatiotemporal architecture of the brain in a 3D fashion. Here we first benchmarked human brain organoids at the level of transcriptomic and structural architecture of cell composition along several stages of differentiation. Then we harnessed their properties to probe the longitudinal impact of GSK3 on human corticogenesis, a pivotal regulator of both proliferation and polarity, that we revealed having a direct impact on early neurogenesis with a selective role in the regulation of glutamatergic lineages and outer radial glia output. Moreover, we spearheaded the use of organoids for regulatory toxicology through the study of Endocrine disrupting chemicals (EDC), pervasive compounds that can interfere with human hormonal systems. Early life exposure to EDC is associated with human disorders, but the molecular events triggered remain unknown. We developed a novel approach, integrating epidemiological with experimental biology to study the mixtures of EDC that were associated with neurodevelopmental and metabolic adverse effects in the biggest pregnancy cohort profiled so far. Our experiments were carried out on two complementary models i) human fetal primary neural stem cells, and ii) 3-dimensional cortical brain organoids and we identified the genes specifically dysregulated by EDC mixture exposure, unravelling a significant enrichment for autism spectrum disorders causative genes, thereby proposing a convergent paradigm of neurodevelopmental disorders pathophysiology between genetic and environmental factors. Finally, while EDCs are everywhere, their impact on adverse health outcomes can vary substantially among individuals, suggesting that other genetic factors may play a pivotal role for the onset of the disorders. We took advantage of organoids multiplexing to recapitulate, at the same time, neurodevelopmental trajectories on multiple genetic backgrounds, and showed that chimeric organoids preserved the overall morphological organization and transcriptomic signatures of the ones generated from single lines. In conclusion our work shows the possibility to perform population level studies in vitro and use the deep resolution of molecular biology to dissect key aspects of human neurodevelopment.