Annular gap junctions of the equine hoof wall.

This research was conducted to study the process of keratinization in the equine hoof wall and in the process, findings were made about the existence and role of annular gap junctions in the stratum spinosum of the intertubular horn of the stratum medium.

Overview of the Study

• The researchers were originally focused on studying the process of keratinization of the equine hoof wall. Keratinization refers to the process by which keratin (a protein) is deposited in cells, strengthening and waterproofing the tissue.
• During this study, they discovered annular gap junctions in the stratum spinosum layer of the intertubular horn in the middle stratum (stratum medium) of the hoof wall.

Observations and Suggestions

• Adjacent cells of the stratum spinosum, a layer of the epidermis, showed extensive gap junctions. Gap junctions are specialized intercellular connections that directly connect the cytoplasm of two cells, facilitating various forms of transport and communication between them.
• Often there were observed local invaginations – inward folds – of one cell into another, with these invaginations bound by gap junctions.
• The researchers propose that these invaginations may become detached from the cell surface, forming what they refer to as annular gap junctions.

Role and Implications of Annular Gap Junctions

• The formation of annular gap junctions may serve as a mechanism for disposing of plasma membrane resulting from changes in cellular volume or shape during the keratinization process.
• The internalization (movement toward the interior of a cell) of gap junctions may facilitate cell movement, possibly aiding in the reorganization of desmosome-tonofibril arrangements (critical elements in cell adhesion).
• This arrangement may result in desmosomes – adhesive structures that bind cells to one another – being brought closer together. The researchers suggest this could occur by budding off appropriate areas between desmosomes (interdesmosomal areas), thereby drawing the desmosomes closer to one another.