MiR-202 Is Required For Zebrafish Embryonic Development

miRNAs are endogenous non–coding RNAs with approximately 22 nt in length,which play important regulatory roles in gene expression. miRNAs regulate series of physiological and pathological processes as well as developmental processes.Zebrafish as a model organism of vertebrate has many advantages in developmental biological studies. Characters, such as its small size, high fecundity, shorter life cycle, larger capacity for generating offspring, an annotated and sequenced genome, perfect embryos and genetic manipulation technologies, make zebrafish as a fundamental experimental model to study miRNA function, embryonic development mechanisms and evolution.Previous studies in our laboratory showed that miR-202, a member of let-7 family, is highly conserved across the vertebrata, but is absent in the genome of a primitive chordata, Amphioxus, implying a vertebrate specific role of miR-202. Expressional study showed that miR-202 is specifically expressed in gonads. However, the function of miR-202 in embryonic development is unclear. Using the vertebrate model of zebrafish, we commenced the researches to elucidate the functions of miR-202 in zebrafish embryonic development.Firstly, the temporal and spatial expression of mir-202 was studied using qRT-PCR and whole mount in situ Hybridization(WISH), we found miR-202 was abundantly present in the embryos of the zebrafish at stages of 0 pdf to 72 pdf. Secondly, we found knocking down of miR-202 led to developmental arrest at around 4 hpf, which ultimately leads to embryo mortaility. The developmental arrest could be rescued by co-injection of miR-202 precursor. Thirdly, we deleted the miR-202 coding region using the CRISPR/Cas9 system. No significant differences in the developmental processes were observed between the F1 heterozygotes and the wild type zebrafish embryos. However, the F2 homozygotes embryo exhibited abnormal embryonic development and died within 5 hpf-24 hpf.In conclusion, current study indicated that miR-202 is required for zebrafish embryonic development. The molecular details of mir-202 functions await further investigation.