Mucocutaneous junction of eyelid and lip: a study of the transition zone using epithelial cell markers

The expression of epithelial cell markers in the mouse eyelid and lip was investigated in order to understand the nature of the interactions of mucosal and skin epithelium as to how they form the mucocutaneous junction (MCJ).

Cryosections of eyelid and lip tissue from normal mice were examined immunohistochemically with cytokeratins (CKs): CK1, CK4, CK5, CK6, CK10, CK13, CK14, and CK19; filaggrin; involucrin; and connexin 43.

The expression pattern varied across the MCJ, with the absence of CK1, CK10, and filaggrin in the mucosal epithelium; and CK4, CK6, and CK13 in the skin epidermis. CK5 and CK14 were consistently expressed in full-thickness skin, MCJ, and mucosa. CK19 was expressed basally, while involucrin-positive cells were found superficially in skin, MCJ, and mucosa. Connexin 43 was present in the MCJ, skin, and labial mucosa; however, little to no expression was seen in the palpebral conjunctiva.

The MCJ may be a focal point of mucosal epithelial cell differentiation activities. The similarity of staining patterns in the eyelid and lip suggests that the formation of these sites of shared interaction between the internal and external environment employs similar cellular mechanisms.