UTX expression is critical for PGC migration in zebrafish. (A) Treatment of zebrafish embryos at the 1-cell stage with UTX-specific morpholinos (UTX MO) resulted in significantly reduced migration of PGCs to the main cluster. Coinjection of MO-resistant UTX mRNA significantly restored migration of PGC to the main cluster. (B) Representative images of zebrafish embryos injected at the 1-cell stage with control MO, UTX MO, or UTX MO + MO-resistant UTX mRNA and stained for Vasa mRNA 24 hours after fertilization in situ. Red arrowhead indicates the normal position of the germ cell cluster in the embryo, whereas black arrowheads show ectopic positions. ***P < .001. MO, morpholino; ns, not significant.