Morphology

Fin morphology (skeleton; caudal fin)

wild-type fish

double tail mutant

Taxon A

Domesticated

No

Cis-regulatory

Deletion

100-999 bp

"We further sequenced the genomes of both homozygous single- and double-tail fish and found in double tail no large sequence variation except for a ∼180-bp deletion ∼15-kb downstream of zic4 (fig. 4C and supplementary fig. S19a, Supplementary Material online). This deletion was located in a cluster of CNEs and coincided with predicted CNE.006008 (supplementary fig. S19b, Supplementary Material online)."

"We observed that the wild-type ST allele significantly enhanced green fluorescent protein (GFP) expression in embryos at 24 hpf, when both zic1 and zic4 show differential expression between double-tail and wild-type fish (Moriyama et al. 2012), whereas no visible GFP expression was detected for the st allele (fig. 4E and supplementary table S11, Supplementary Material online). The efficiency of the two alleles as candidate enhancers was further examined using a Dual-Luciferase Reporter Assay, which showed that the ST allele enhanced luciferase expression by ∼10× relative to st allele in Singapore grouper embryonic cell line (fig. 4F)."

"Finally, we deleted this enhancer using the CRISPR-Cas9 system in fighting fish. Considering the efficiency of tested gRNAs and the cluster of CNEs that could have unpredicted functions, we limited the modification to the CNE.006008 region and did not involve the other CNEs (supplementary fig. S20, Supplementary Material online). Genetic analysis revealed that none of these fish had completely deleted CNE.006008, suggesting nonsimultaneous cutting at multiple targeted gRNA positions. These mosaic fish (n = 7) had significantly more fin rays than the noninjected controls (P < 0.01; fig. 4G). "

Linkage Mapping