Zebrafish hoxb7a mutants exhibit no apparent morphological abnormalities, despite being the only paralogous group 7

During the development, Hox genes play a crucial role in providing positional information and timing along the body axes. Vertebrates possess more than four Hox clusters due to whole-genome duplications, with each cluster essentially consisting of 13 paralogous groups. In mice, there is functional overlap among 39 Hox genes across these clusters; disrupting all Hox genes within the same paralogous group leads to significant abnormalities. Zebrafish have undergone additional teleost-specific duplication, resulting in 49 hox genes distributed among seven clusters. Unique among the paralogous groups, zebrafish paralogous group 7 contains only one hox gene, hoxb7a. Disrupting hoxb7a may provide insights into the overall function of paralogous group 7 during development. In this study, we utilized the CRISPR-Cas9 system to generate zebrafish hoxb7a frameshift mutants. Despite the frameshift mutation resulting in truncated proteins lacking the homeodomain, we observed no significant morphological defects or reduced survival rates in hoxb7a homozygous mutants. Furthermore, micro-CT scanning of adult hoxb7a mutant zebrafish did not reveal any major abnormalities in their skeletal structures or soft tissues. Phylogenetic analysis confirmed that hoxb7a is the sole gene in paralogous group 7. The absence of apparent defects in hoxb7a mutants suggests potential functional redundancy among hox genes in neighboring paralogous groups during zebrafish development.