Exploration of Dentition Development and Replacement in Two Forms of Mexican Tetra (<scp><i>Astyanax mexicanus</i></scp>)

There are two main subforms of the teleost fish Mexican tetra (Astyanax mexicanus): the river-dwelling surface fish and the cave-dwelling blind cavefish. Recently, this species has become a popular animal model in developmental biology research. It was reported that cavefish bore more teeth than surface fish; however, a detailed description of oral dentition development and replacement in the Mexican tetra remains unavailable. In this study, we investigated the differences in tooth count between surface fish and cavefish by characterising the features of mandibular dentition in adult Mexican tetras and explored the process of first-generation dentition development in larval fish. Regarding early dentition development, larval surface fish and Pachón cavefish at 12-, 18-, 21-, 24-, and 30-days post-fertilisation were euthanised. Haematoxylin and eosin staining was performed for histological analysis, and immunohistochemistry was employed to detect the expression of the odontogenic marker Sox2. The results show that Mexican tetras replaced functional teeth via the successional dental lamina marked by Sox2 expression. Adult Pachón cavefish possessed more intraosseous replacement teeth. Mandibular tooth development in larval fish was also marked by Sox2 expression, and no evidence supported tooth development in a continual dental lamina. Our findings describe the appearance of a successional dental lamina in tooth replacement in the Mexican tetra but provide no evidence regarding a continual dental lamina. In the Mexican tetra, teeth of the first-generation dentition may develop independently. The results of this project will offer valuable histological information for future research into tooth development in the Mexican tetra.