CLDN4 and type 1 diabetes mellitus: In differentiated enteroids with more mature junctional complex, there were significant differences in the expression of tight junction proteins: T1D enteroids had significantly increased mRNA for claudin 4 (CLDN4), ZO2, and 3 but no change in ZO1; in addition, there was a significant decrease in expression of claudin 23 (CLDN23) (Fig. 4e).