Zebrafish (Danio rerio) adults and embryos were maintained at 28.5 °C under standard protocols (41 (link)). The following strains were used: the mixed wild-type ABxTU, Tg(wt1b:EGFP)li1 (42 (link)), Tg(cmlc2:GFP), and Tg(bactin:arl13bGFP)hsc5Tg (43 (link)) to label proximal pronephros, heart, and cilia, respectively. MO, designed to target the 5′ Stem-Loop (5’SL) (5′-GATGTTCTCAGTTAACCTTCATTGA-3′) or the Stem II (SII) (5′-AAACCACCCCCAGACAAGGAA-GGTT-3′) regions of u4atac_chr11, were provided by GeneTools, LCC and injected into the yolk at the one-cell stage (quantity ranging from 0.016 to 0.066 pmol (i.e., 135 to 556 pg) per embryo for 5’SL MO and 0.002 to 0.006 pmol (i.e., 17 to 51 pg) per embryo for SII MO). A five-mismatch MO (5′-GATcTTgTCAcTTAACCTTgATTgA-3′) was used as a negative control. For rescue experiments, snRNA molecules were synthesized using the MAXIscript T7 Transcription Kit (ThermoFisher Scientific); DNA templates of human U4atac snRNA sequence were PCR-amplified from previously described plasmids (9 (link)) (SI Appendix, Table S3). snRNA molecules were purified with Clean and Concentrator kit (Zymo Research), and 65 pg were coinjected with u4atac MO per embryo.