CLDN1 and colitis: Mice with a mutated Per2 gene(mPer2m/m) showed constitutively high levels of occludin and claudin-1 proteins and were more resistant to dextran sulfate sodium (DSS)-induced colitis, whereas ClockΔ19/Δ19 mice showed decreased levels of these tight junction proteins and were more susceptible to DSS-induced colitis [42].