Emerging evidence from the current outbreak of Zika
virus (ZIKV) indicates a strong causal link between
Zika and microcephaly. To investigate how ZIKV
infection leads to microcephaly, we used human
embryonic stem cell-derived cerebral organoids to
recapitulate early stage, first trimester fetal brain
development. Here we show that a prototype strain
of ZIKV, MR766, efficiently infects organoids and
causes a decrease in overall organoid size that correlates
with the kinetics of viral copy number. The innate
immune receptor Toll-like-Receptor 3 (TLR3) was upregulated
after ZIKV infection of humanorganoids and
mouse neurospheres and TLR3 inhibition reduced the
phenotypic effects of ZIKV infection. Pathway analysis
of gene expression changes during TLR3 activation
highlighted 41 genes also related to neuronal
development, suggesting a mechanistic connection
to disrupted neurogenesis. Together, therefore, our
findings identify a link between ZIKV-mediated TLR3
activation, perturbed cell fate, and a reduction in organoid
volume reminiscent of microcephaly.