The discovery of epidermal tight junctions

Area of Science:

• Dermatology
• Cell Biology
• Microscopy

Background:

• The skin barrier was historically attributed solely to the stratum corneum.
• The existence of tight junctions in the epidermis, specifically in the stratum granulosum, was proposed in 2002.
• Earlier research in 1971 by Hashimoto et al. suggested tight junctions in the epidermis using lanthanum penetration studies.

Purpose of the Study:

• To re-evaluate early findings on epidermal tight junctions.
• To emphasize the significance of careful observation in scientific research.
• To connect historical observations with modern molecular biology discoveries.

Main Methods:

• Electron microscopy of human skin injected with lanthanum nitrate.
• Observation of lanthanum penetration through epidermal intercellular spaces.
• Confirmation of tight junctions through the discovery of claudin proteins.

Main Results:

• Lanthanum penetration was halted in the granular cell layer, indicating the presence of tight junctions.
• Hashimoto's 1971 findings of 'truly tight junctions' were initially overlooked.
• The discovery of claudins in 2002 validated the existence of epidermal tight junctions.

Conclusions:

• Hashimoto's early observations were retrospectively confirmed three decades later.
• The discovery of claudins was crucial in validating the presence of tight junctions between epidermal keratinocytes.
• This case underscores the importance of persistent and careful observation in advancing scientific understanding, even in the molecular biology era.