The causal link between maternal Zika virus (ZIKV) infection and neonatal microcephaly is now well established, but the factors that render the immature brain particularly susceptible to ZIKV are still being explored. A new study published in Science has identified the RNA-binding protein Musashi-1 (MSI1) as a possible mediator of the effects of ZIKV on the developing brain. The research team, led by Fanni Gergely at the MRC Laboratory of Molecular Biology in Cambridge, UK, showed that MSI1 could bind to ZIKV RNA and promote replication of the viral genome in neural cell lines. MSI1 is expressed at high levels in neural progenitor cells in the developing human brain, and a mutation in the MSI1 gene has previously been implicated in autosomal primary microcephaly. Taken together, the data build a convincing case for MSI1 as a determinant of the vulnerability of the fetal brain to ZIKV.