Extensive loss of HoxA/D genes does not disrupt anterior vertebral patterning in zebrafish

Hox genes play central roles in specifying positional identities along the vertebrate anterior-posterior axis. In mice, genetic analyses have demonstrated that Hox genes distributed among the four Hox clusters contribute to vertebral patterning, with extensive functional redundancy among paralogous genes. Our previous genetic analysis in zebrafish identified important roles for HoxB- and HoxC-related genes in specifying anterior vertebral identities, whereas the contributions of HoxA- and HoxD-related genes remained unresolved. Here, we examined adult zebrafish carrying extensive combinations of hoxaa, hoxab, and hoxda cluster deletions and generated five-gene homozygous mutants carrying frameshift mutations in hoxa3a, hoxa4a, hoxa5a, hoxd3a, and hoxd4a. X-ray micro-CT analysis revealed no obvious alterations in anterior vertebral morphology in either the compound cluster mutants or the five-gene mutants. These results indicate that HoxA/D genes make only a limited detectable contribution to anterior vertebral patterning in zebrafish. Together with our previous findings, they suggest that vertebral patterning functions are distributed unevenly among zebrafish Hox clusters, with a predominant contribution from HoxB/C-related genes.