Mapping the Cellular Landscape of Zebrafish Posterior Intestine: Insights into the Epithelial, Cup-, and Immune Cells...

Although the zebrafish (Danio rerio) is widely used as a model for gastrointestinal research, a comprehensive, multi-modal characterization of the adult posterior intestine has not previously been reported. In this study, we present the first integrated histological, ultrastructural, and immunofluorescent atlas of the adult zebrafish posterior intestine, together with normative morphometric reference data for distinct intestinal cell populations. Notably, we identify, for the first time, vimentin-positive cup cells exhibiting ultrastructural characteristics consistent with mammalian M cells. We also provide the first evidence of telocytes within the zebrafish posterior intestinal wall, distinguished by their moniliform telopodes and fibronectin immunoreactivity. Furthermore, the unexpected localization of fibronectin within the enterocyte cytoplasm suggests a previously unrecognized role in epithelial barrier organization and maintenance. The detection of SOX9 immunoreactivity in basally positioned epithelial cells is consistent with the presence of a putative progenitor cell population that warrants further functional investigation. Together, these findings establish a comprehensive morphological and morphometric reference framework for the adult zebrafish posterior intestine, providing a valuable foundation for studies of vertebrate intestinal biology, epithelial homeostasis, mucosal immunity, and comparative gastrointestinal research.