A pivotal contribution of proteostasis failure and mitochondria dysfunction to Chromosomal Instability-induced microcephaly

Mosaic variegated aneuploidy (MVA), a rare human congenital disorder that causes microcephaly, is characterized by extensive abnormalities in chromosome number and caused by mutations in genes involved in accurate mitotic chromosome segregation. Here we generated a Drosophila model of microcephaly caused by depletion of a single spindle assembly checkpoint (SAC) gene in the neural stem cell (NSC) compartment to characterize the cellular mechanisms underlying this disease. We present evidence that loss of stemness of NSCs – compromised identity and proliferative capacity - is the underlying cause of the disease and results in a reduced number of neurons and glial cells. We show that loss of stemness is a consequence of the accumulation overtime of an unbalanced number of gains and losses of more than one chromosome, rather than a direct consequence of chromosomal instability-induced DNA damage or the production of simple aneuploidies. We unravel a contribution of proteostasis failure, most probably as a consequence of the imbalance in the whole protoeome, and mitochondria dysfunction to the negative impact of complex aneuploidies on stem cell identity. We identify autophagy activation -either directly or through TOR depletion –, overexpression of Radical Oxygen Species scavengers, or restoration of mitochondria proteostasis as genetic interventions capable of dampening the deleterious effects of aneuploidy on NSC identify and brain development Overall design: The samples used for this study are late L3 larvae from Drosophila melanogaster (96 hours after egg laying at 29 ºC). For the control, we have used w; worniu-gal4, UAS-gfp-i larvae. For the experimental condition, we have used w; worniu-gal4, UAS-bub3-i larvae. 3 replicates from different days were performed and 3 brains were dissected per each genotype and per replicate. All the larvae used were females.