CNS defects in hif2α morphants are rescued by ectopic injection of survivin orthologue mRNA. The percentages of normal, moderate and severe (characterized by a smaller head size, short curved tail, narrow somites and massive CNS apoptosis) morphological phenotypes in the WT (n=50), hif1α ATG-MO (n=54), hif2α ATG-MO (n=69), hif2α SPL-MO (n=23), hif3α ATG-MO (n=25), hif1α, 3α dual ATG-MO (n=64), birc5a ATG-MO (n=45), birc5b ATG-MO (n=35) 48 h.p.f. embryos and hif2α ATG-MO co-injected with 50 pg birc5a mRNA (n=167) and in the hif2α ATG-MO embryos co-injected with 50 pg birc5b mRNA (n=262). Ectopic injection of either birc5a or birc5b mRNA restored most hif2α morphants to a normal phenotype whereas birc5a mRNA had better rescuing capability