Effects of microRNA 133 on developing zebrafish (Danio rerio) embryos

MicroRNAs (miRs) are a family of small non-coding RNAs that regulate the expression of numerous downstream mRNAs. Cardiac dysfunction in early life stage mahi-mahi (Coryphaena hippurus) exposed to crude oil has been associated with upregulation of miR133b and subsequent downregulation of genes important for proper heart development, similar to mammals. To directly test the potential role of miR133b in oil-induced early life-stage cardiotoxicity in fish, cleavage-stage zebrafish (Danio rerio) embryos were microinjected with a miR133b mimic. At 72 hours post-fertilization (hpf), miR133b-injected fish exhibited oil-like cardiovascular malformations relative to negative control miR-injected embryos. Phenotypic effects outside of the heart were not observed. Gene expression analysis showed that at 5 hpf miR133b decreased the abundance of cardiac-specific IKr kcnh6 and ryanodine receptor 2, a crucial calcium receptor in the sarcoplasmic reticulum. Together results demonstrate that miR133b may target cardiac tissues in teleost, similar to vertebrates, and contribute to cardiac perturbations in oil-exposed fish by targeting genes essential for proper heart development.