Phenotype Analysis and Mechanism of the Zebrafish eomesa^fh105 Mutant Without Dorsal Fin

From an evolutionary perspective, limbs of tetrapods are homologous organs to paired fins of fishes, and the regulation pattern of their formation and development is becoming clear. The unpaired fin is the ancestor of the paired fins, and its developmental regulation pattern is similar to that of the paired fins. However, the detailed mechanism is still unknown. In this study, the developmental process of dorsal fin of both wild-type and eomesa^fh105 mutant without dorsal fin was observed, the skeletal morphology of dorsal fin of wild-type and mutant was analyzed with alcian blue and alizarin red double staining, the expression pattern and position of eomesa was analyzed by qPCR and in situ hybridization technique. Finally, transcriptome analyses of whole bodies of wild-type and mutants at three points of standard body length（SL） were performed. The results showed that the dorsal fin bud was formed when the standard body length of wildtype was about 6.3 mm, and the dorsal fin was mostly formed when SL was about 7.5 mm. However, the dorsal fin bud of mutant could not be formed or develop normally, resulting in the phenotype of absence of dorsal fin in zebrafish. Bone staining showed that the defects of dorsal fin in the mutants could be classified into three types. It was showed that eomesa was expressed in the brain and not in the dorsal fin detected by qPCR and in situ hybridization. The transcriptome analysis showed that there were 19 shared up-regulated genes and 5 shared down-regulated genes among the deferentially expressed genes at the three SL points. This study demonstrats that eomesa may not be the key gene which induces the fin bud initiation, but affects the formation or outgrowth of fin bud, which finally results in several phenotypes of dorsal fin absence in mutants.