is a broadly and highly expressed microRNA in the developing brain and is frequently deleted in 5q14.3 Microdeletion Syndrome, a rare but severe neurodevelopmental disorder. Despite this, little attention has been paid to the unique contributions of to neurodevelopment and disease. We find that deletion of this microRNA leads to embryonic cerebral hemorrhages and severe hydrocephalus, while disrupting gene networks across a wide range of cell types in the developing brain, thus revealing underappreciated and non-redundant molecular, cellular, and system-wide functions for in neurodevelopment.