Claudin-based tight junctions are crucial for the mammalian epidermal barrier: a lesson from claudin-1–deficient mice Claudin-1-deficient mice die within 1 day of birth with wrinkled skin and severe epidermal barrier defects. These findings indicate that claudin-1 is essential for maintaining the epidermal barrier function. Claudin-1 is a component of tight junctions (TJs) in the epidermis, and its absence leads to the loss of TJ continuity and increased permeability. The study shows that claudin-1 is concentrated in TJs in the stratum granulosum, and its removal results in the loss of TJ continuity and increased permeability. The epidermis of claudin-1-deficient mice shows no obvious abnormalities in the layered organization of keratinocytes, but the epidermal barrier is severely affected. The study also shows that claudin-1 is involved in the barrier function of the epidermis, and its absence leads to increased permeability. The study provides the first evidence that continuous claudin-based TJs occur in the epidermis and that these TJs are crucial for the barrier function of the mammalian skin. The study also shows that claudin-1 is involved in the formation and maintenance of TJs in the epidermis. The study highlights the importance of claudin-1 in the barrier function of the epidermis and suggests that claudin-based TJs are crucial for the barrier function of the mammalian skin.Claudin-based tight junctions are crucial for the mammalian epidermal barrier: a lesson from claudin-1–deficient mice Claudin-1-deficient mice die within 1 day of birth with wrinkled skin and severe epidermal barrier defects. These findings indicate that claudin-1 is essential for maintaining the epidermal barrier function. Claudin-1 is a component of tight junctions (TJs) in the epidermis, and its absence leads to the loss of TJ continuity and increased permeability. The study shows that claudin-1 is concentrated in TJs in the stratum granulosum, and its removal results in the loss of TJ continuity and increased permeability. The epidermis of claudin-1-deficient mice shows no obvious abnormalities in the layered organization of keratinocytes, but the epidermal barrier is severely affected. The study also shows that claudin-1 is involved in the barrier function of the epidermis, and its absence leads to increased permeability. The study provides the first evidence that continuous claudin-based TJs occur in the epidermis and that these TJs are crucial for the barrier function of the mammalian skin. The study also shows that claudin-1 is involved in the formation and maintenance of TJs in the epidermis. The study highlights the importance of claudin-1 in the barrier function of the epidermis and suggests that claudin-based TJs are crucial for the barrier function of the mammalian skin.