The purP0se of this investigation was to find out whether C-terminally end-cleaved aquaP0rin 0 (AQP0), that is present predominantly in the lens mature fiber cells of the WT, functions as a water channel and a cell-to-cell adhesion (CTCA) protein in a knockin (KI) mouse model (AQP0(Delta C/Delta C)) that does not express intact AQP0. A genetically engineered KI mouse model, AQP0(Delta C/Delta C), expressing only end-cleaved AQP0 was developed. This model expresses 1-246 amino acids of AQP0, instead of the full length 1-263 amino acids. Lens transparency of P0stnatal day 10 (P10) was analyzed qualitatively by dark field imaging. WT, AQP0(+/-) and AQP0(+/Delta C) lenses were transparent; AQP0(-/-) and AQP0(Delta C/Delta C) mouse lenses displayed loss of transparency. Lens fiber cell membrane vesicles (FCMVs) were prepared from wild type (WT), AQP0 heterozygous (AQP0(+/-)), AQP0 knockout (AQP0(-/-)), AQP0(+/Delta C) and AQP0(Delta C/Delta C); water permeability (p(f)) was measured using the osmotic shrinking method. CTCA assay was performed using adhesion-deficient L-cells and FCMVs prepared from the abovementioned genotypes. FCMVs of AQP0(+/-) and AQP0(-/-) showed a statistically significant reduction (P < 0.001) in P-f and CTCA compared to those of WT. AQP0(Delta C/Delta C) and AQP0(Delta C/Delta C) FCMVs exhibited no statistically significant alteration (P > 0.05) in P-f compared to those of WT. However, CTCA of AQP0(+/Delta C) AQP0(Delta C/Delta C) FCMVs was significantly higher (P < 0.001) than that of WT FCMVs. Our experiments clearly show that C-terminally end-cleaved AQP0 can function both as a water channel and a CTCA molecule in the lens fiber cell membranes. Also, end-truncation plays an important role in increasing the CTCA between fiber cells. (C) 2019 Elsevier Inc. All rights reserved.