Yoshitaka Tanaka: Department of Ecological Developmental Adaptability Life Sciences, Graduate School of Life Sciences, Tohoku University, Sendai 980-8578, Japan. ORCID
Shun Okayama: Department of Ecological Developmental Adaptability Life Sciences, Graduate School of Life Sciences, Tohoku University, Sendai 980-8578, Japan.
Kohei Urakawa: Department of Developmental Biology, Integrated Medical Sciences, Graduate School of Medical Sciences, Tottori University, Yonago 683-8503, Japan.
Hidehiro Kudoh: Department of Ecological Developmental Adaptability Life Sciences, Graduate School of Life Sciences, Tohoku University, Sendai 980-8578, Japan.
Satoshi Ansai: Laboratory of Genome Editing Breeding, Graduate School of Agriculture, Kyoto University, Kyoto 606-8507, Japan. ORCID
Gembu Abe: Department of Ecological Developmental Adaptability Life Sciences, Graduate School of Life Sciences, Tohoku University, Sendai 980-8578, Japan. ORCID
Koji Tamura: Department of Ecological Developmental Adaptability Life Sciences, Graduate School of Life Sciences, Tohoku University, Sendai 980-8578, Japan. ORCID
Pectoral fins, the anterior paired fins in fish, have enhanced maneuvering abilities due to morphological changes. Teleosts have fewer radial bones in their pectoral fins than basal species, resulting in more-elaborate fins. The mechanism behind this radial constraint change in teleosts is unclear. Here, we found that mutations in hhip, which encodes an antagonist of Hedgehog signaling, led to an increase in radial bones in a localized region. Expression of the Shh genes, encoding ligands of Hedgehog signaling, coincided with notable hhip expression specifically during early development. We suggest that a negative feedback effect of Hedgehog signaling by hhip regulates the constraint of the pectoral fin in zebrafish. Additionally, re-analysis of hhip-related gene expression data in zebrafish and basal species revealed that the notable hhip expression during early development is a characteristic of zebrafish that is not observed in basal species. Region-specific expression of Hox13 genes in the zebrafish pectoral fin indicated that the median region, analogous to the region with abundant radials in basal species, is expanded in hhip-/- zebrafish. These data underscore potential morphological evolution through constrained diversity.
