The microcephaly gene aspm is involved in brain development in zebrafish

► We identified a zebrafish aspm/mcph5 gene that is expressed in proliferating cells in the CNS during early development. ► Embryos injected with the aspm MO consistently showed a reduced head and eye size but were otherwise grossly normal, closely mimicking the known phenotypes of human microcephaly patients. ► Knock-down of aspm causes cell cycle arrest and apoptotic cell death during early development. MCPH is a neurodevelopmental disorder characterized by a global reduction in cerebral cortical volume. Homozygous mutation of the MCPH5 gene, also known as ASPM, is the most common cause of the MCPH phenotype. To elucidate the roles of ASPM during embryonic development, the zebrafish aspm was identified, which is specifically expressed in proliferating cells in the CNS. Morpholino-mediated knock-down of aspm resulted in a significant reduction in head size. Furthermore, aspm-deficient embryos exhibited a mitotic arrest during early development. These findings suggest that the reduction in brain size in MCPH might be caused by lack of aspm function in the mitotic cell cycle and demonstrate that the zebrafish can provide a model system for congenital diseases of the human nervous system.