ANKLE2 and microcephaly: To support this idea further, we found that expression of NS4A in a fly that is in a genetically sensitized background for Ankle2 (heterozygous for a hypomorphic allele of Ankle2) caused a significantly stronger microcephaly phenotype compared to flies that express NS4A in a wild-type background, demonstrating that Zika NS4A and fly Ankle2 genetically interact in vivo.