Ocular coloboma phenotype and partial rescue in  rarga morpholino (MO) knockdown zebrafish embryos. (a)  rarga MO‐injected embryos show a slightly smaller body and head sizes compared with uninjected zebrafish embryos at 48 hr postfertilization (hpf). (b) Uninjected wild‐type with normal eye. (c) Standard control MO‐injected embryos. Ocular size is comparable to the wild‐type uninjected embryos and both reveal no coloboma in the eye or other phenotypes at 3.75–7.5 ng MO concentrations. (d–e)  rarga MO‐injected embryos revealed concentration‐dependent ocular coloboma as Grade 2 (narrow, d) or Grade 3 (wide, e) optic fissure closure defects. The red bars indicate the margins of the optic fissure. Scale bar in (e) applies to panels b–e. (f)  rarga transcript expression by qRT‐PCR was significantly reduced in MO knockdown zebrafish embryos; *** p < .001. (g) Human  RARB mRNA but not  RARB‐mutant mRNA partially reduced the coloboma phenotype in  rarga MO knockdown embryos. Embryos were injected with  rarga splice‐blocking MO along with either human wild‐type  RARB or  RARB‐mutant mRNA and coloboma phenotype was analyzed after 48 hpf. The values on the bars represent the number of embryos injected or analyzed. qRT‐PCR, quantitative real‐time polymerase chain reaction; mRNA, messenger RNA