Investigating dentition development and replacement in Mexican tetra two subforms

Mexican tetra (Astyanax mexicanus) is a teleost fish which has become a popular animal model in developmental biology research. There are two main subforms in Mexican tetra: the river-dwelling surface fish and cave-dwelling blind fish. Previous studies have indicated that cavefish possess a greater number of teeth compared to surface fish. However, detailed understanding of tooth development and replacement in Mexican tetra remains limited. This project aimed to explore the potential causes behind the differences in tooth count between surface fish and cavefish by characterizing the features of the mandibular dentition in adult surface fish and Pachon cavefish and by describing the process of first generation of dentition development in larval fish. Surface fish and Pachon cavefish were sacrificed to investigate the normal dentition of adult Mexican tetra. Tissue processing was carried out on mandible samples, followed by the preparation of transverse histological sections. For the study of early dentition development, larval Mexican tetra surface fish and Pachon cavefish at 12-, 18-, 21-, 24-, and 30-days post-fertilization were sacrificed for histological analysis. Additionally, immunohistochemistry was employed to detect the expression of the odontogenic marker Sox2. Results indicated that Mexican tetras replace their functional teeth via successional dental lamina marked by Sox2 expression. Compared to adult surface fish, adult Pachon cavefish possess more intraosseous replacement teeth. In early dentition development, the development of mandibular teeth was marked by Sox2 expression. No continual dental lamina was observed, nor were there significant morphological differences in developmental structures between the two subforms. Our findings confirm the morphology and localization of successional dental lamina in tooth replacement in Mexican tetra but provide no evidence that the first dentition develops according to a continual dental lamina pattern. The first