Abstract: The zebrafish hoxb7a gene is the only gene in the seventh paralogous group of hox genes in the evolution of the third genome duplication. In order to study the function of hoxb7a gene in the whole hox gene clusters, we knocked out the zebrafish hoxb7a by using CRISPR/Cas9 technology. The hoxb7a mutagenesis efficiency was about 43% which was evaluated by T7E1 assay in F0. And we successfully obtained two mutant fish lines of hoxb7a, which were 8 bp deletion and 23 bp deletion. Furthermore, we used QPCR technology to compare the related hox genes expression level changing of wide type zebrafish embryos with that of hoxb7a-/-at 48hpf (hour post fertilization). And the QPCR results showed that the hox genes closed to hoxb7a in the genome were significantly up-regulated (P<0.001), however, the hox genes far away from hoxb7a in the genome had no obvious difference(P>0.05)in hoxb7a mutants comparing with the wide type. This study demonstrated that hoxb7a plays a crucial role in hox clusters, which deepens the understanding of the functional differentiation of duplicate hox genes. At the same time, we successfully established the hoxb7a mutant, which provides a foundation for future mechanism studies on the hoxb7a gene function.

Key words: zebrafish, CRISPR/Cas9 system, hoxb7a gene, hox clusters, paralogous gene