show Abstracthide AbstractEarly embryonic development is driven by maternal gene products deposited into the oocyte. Due to the lack of reliable knockdown strategies, maternal mRNA functions have remained elusive. CRISPR-Cas13 systems have recently been employed to induce RNA degradation in yeast, plants and mammalian cell lines. However, no systematic study of the potential of Cas13 has been carried out in an animal model system. Here, we show that CRISPR-Cas13d is an effective and precise system to deplete specific mRNA transcripts in zebrafish embryos. We demonstrate that both zygotically-expressed and maternally-provided transcripts are efficiently targeted, resulting in an 85% average decrease in transcript level and the recapitulation of well-known embryonic phenotypes. Moreover, we show that this system can be used in medaka, killifish, sea anemone and mouse embryos. All together our results demonstrate that CRISPR-Cas13d is an efficient knockdown platform to understand gene function in animal embryos. Overall design: Zebrafish embryos were injected with the indicated mRNA and/or guideRNAs and after 6 hours post injection.There are two biological replicates per treatment.