Which protein is primarily involved in the formation of tight junctions?

Tight junctions are critical structures in epithelial and endothelial tissues that form a selective barrier, regulating the passage of ions and molecules between cells. The primary proteins involved in the formation of tight junctions are claudins. These are a family of proteins that span the cell membrane and interact with similar proteins in adjacent cells to create the tight seal characteristic of these junctions. Claudins are essential in determining the permeability of tight junctions, thereby influencing various physiological processes.

While catenins, cadherins, and integrins play important roles in cell adhesion and communication, they are not the principal proteins that form tight junctions. Catenins and cadherins are primarily associated with adherens junctions, which provide strength and stability to cell-cell contacts but do not create the barrier function that tight junctions are known for. Integrins, on the other hand, are involved in cell-extracellular matrix interactions and cell signaling but do not contribute directly to the tight junctions' structure. Therefore, claudins are the key proteins specifically involved in tight junction formation, making this the correct answer.