YAP1-dependent regulation of cell size in BCAM-positive limbal corneal progenitor cells

Cell size has been associated with stem and progenitor cell states across multiple tissues, yet its regulation in the human corneal epithelium remains incompletely understood. This study aimed to characterize cell-size differences among limbal and corneal epithelial cell populations defined by the limbal stem cell (LSC) marker ABCB5 and the transit-amplifying cell (TAC) marker BCAM, and to investigate the molecular regulators of progenitor cell size. ABCB5-positive LSCs and BCAM-positive TACs were identified and isolated by flow cytometry, and the mean cell size was estimated using forward scatter (FSC). As a result, ABCB5-positive LSCs were significantly smaller than ABCB5-negative limbal epithelial cells, and BCAM-positive TACs exhibited a smaller cell size than BCAM-negative cells, particularly in the limbus. Immunofluorescence staining showed that Yes-associated protein 1 (YAP1) and BCAM were co-expressed in basal epithelial cells in the human limbus and cornea. Expression of the YAP1 transcriptional target gene CYR61 was elevated in BCAM-positive limbal cells. SiRNA-mediated knockdown of YAP1 or BCAM in cultured human limbal epithelial cells resulted in a significant increase in cell size. These findings identify small cell size as a characteristic feature of limbal BCAM-positive TACs and demonstrate that progenitor cell size is regulated by YAP1 and BCAM, highlighting an interaction between physical cell properties and progenitor function in the corneal epithelium.