Upregulation of MicroRNA miR-9 Is Associated with Microcephaly and Zika Virus Infection in Mice.

Proper growth of the mammalian cerebral cortex, which is determined by expansion and survival of neural progenitors and mature neurons, is crucial for cognitive functions. Here, we show a role of the dosage of microRNA miR-9 in controlling brain size. Cortical-specific upregulation of miR-9 causes microcephalic defects in mice, due to apoptosis, reduced neural progenitor pool, and decreased neurogenesis. Glial cell-derived neurotrophic factor (GDNF) is a target of miR-9, and protects neural progenitors from miR-9-induced apoptosis. Furthermore, Zika virus (ZIKV) infection in embryonic mouse cortex causes reduced numbers in neural progenitors and newborn neurons, and results in upregulation of miR-9, downregulation of its target GDNF. Our studies indicate an association of altered levels of miR-9 and its target GDNF with microcephaly and ZIKV infection in mice.