Adherens junctions in the ocular lens of various species: ultrastructural analysis with an improved fixation

The ultrastructure and distribution of adherens junctions in the intact adult lens of human, chicken, dove, rat, and rainbow trout were studied with thin-section electron microscopy, using an improved fixation containing a mixture of glutaraldehyde, lysine, and tannic acid. The nature of adherens junctions in the fiber-cells of the lens was also verified by immunofluorescence and rhodamine-phalloidin labelings for vinculin and actin. Electron microscopy revealed that adherens junctions of the lens were different ultrastructurally from the desmosomes found only between the lateral epithelial cells of the lens. The adherens junctions had the same structural characteristics as the zonulae adherentes, except that they were macular contacts, not belts. However, cross bridges were evident within the interspace of the junctions. Adherens junctions were located between the fiber-cells, between the epithelial cells and fiber-cells, and between the epithelial cells. They had a characteristic distribution in the "intersections" where three hexagonal fiber-cells met, as seen in cross-sections in all species studied. In addition, adherens junctions and associated actin were found distributed randomly along the entire cell membranes of both wide and narrow sides of cortical fiber-cells in the human, chicken, and dove lenses which have good accomodating capability. However, in the poorly-accomodating lenses of rat and fish, these junctions were seen predominantly on the narrow sides and at the regions of the wide sides that were very close to the "intersections". It is suggested that adherens junctions and associated actin microfilaments are involved in stabilizing the structural integrity of lens cells during accomodation and in preserving a specific lens shape.