16p11.2 locus decelerates subpallial maturation and limits variability in human iPSC-derived ventral telencephalic organoids

Inhibitory interneurons regulate the activity of cortical circuitry, and their dysfunction has been implicated in Autism Spectrum Disorder (ASD). 16p11.2 microdeletions are genetically linked to 1% of ASD. However, there have been few studies of the effects of this microdeletion on interneuron development. Using ventral telencephalic organoids derived from human induced pluripotent stem cells, we investigated the effect of this microdeletion on organoid size, progenitor proliferation and organisation into neural rosettes, ganglionic eminence (GE) marker expression at early developmental timepoints and expression of the neuronal marker, NEUN at later stages. Early deletion organoids exhibited significantly greater variations in size with concomitant increases in relative neural rosette area and the expression of the ventral telencephalic marker, COUPTFII, with significantly increased variability in these properties. Cell cycle analysis revealed a significant increase in total cell cycle length caused primarily by an elongated G1-phase, the duration of which also varied significantly more than normal. Late deletion organoids increased their expression of the neuronal marker NEUN. We propose that 16p11.2 microdeletions increase developmental variability and may contribute to ASD aetiology by lengthening the cell cycle of ventral progenitors, promoting premature differentiation into interneurons. Summary Statement Using 3D-region-specific organoids, we demonstrate that 16p11.2 deletion increases variability and prolongs the cell cycle of human subpallial progenitors by lengthening their G1 phase.