Developmental Genetic Basis of Homeobox Domain Deletion in Pelvic Fin Deficiency.

is important for commercial fishery catch species and is an emerging target for aquaculture production. Notably, has a bizarre morphology and lacks pelvic fins. However, the reason for the lack of pelvic fins remains unclear, ultimately leading to frequent upside-down floating of during breeding and marked consumption of physical energy. Some lineages, including whales, fugu, snakes, and seahorse, independently lost the pelvic appendages over evolutionary time. Do different taxa employ the same molecular genetic pathways when they independently evolve similar developmental morphologies? Through analysis of the gene responsible for appendage localization, Hoxd9, it was discovered that the Hox domain was absent in the gene of , and the gene lacked the Hox9 activation region, a feature not observed in the gene of other fish species. Interestingly, those distinctive characteristics are not observed in the gene of other fish species. To determine the association between the gene characteristics and the pelvic fin deletion in , the full-length cDNA of the gene was cloned, and morphological observations of the species' juveniles were performed using stereomicroscopy and scanning electron microscopy. Thereafter, the tissue localization of Hoxd9a in the species was analyzed at the gene and protein levels. Based on the results, deletion of the Hoxd9a structural domain possibly leads to disruptions in the protein translation and the pelvic fin localization in during its early ontogenetic developmental stage, resulting in the absence of pelvic fins.