Fig. 5

Potential role of voltage-sensing phosphatase (VSP) in trophotaenia epithelial cells and lysosome-rich enterocyte (LRE)-like epithelial cells among animal species. A: a functional model illustrating the absorption of maternal nutrients into trophotaenia through endocytosis in the epithelial cells. Xenotoca eiseni (Xe)-VSP (brown) is predominantly expressed in the apical region of the cells, potentially contributing to the endocytic activity. The absorbed substances are subsequently digested by proteolysis or lipolysis in the intracellular vesicles. B: schematic representation of LRE-like epithelial cells in diverse animal species. LRE-like epithelial cells with high endocytosis activity for nutrient absorption have been identified in absorptive tissues in a wide range of animal species, such as in Ciona intestinalis (digestive epithelium), X. eiseni (enterocytes and trophotaenia epithelium), zebrafish (LREs within the mid-intestine), and newborn mammals (enterocytes within the ileum). Note that VSP (brown) is associated with these LRE-like epithelial cells and has been experimentally validated in C. intestinalis, X. eiseni, and zebrafish.