Distribution of basal membrane complex components in elongating lens fibers

Purpose: To localize specific components of the Basal Membrane Complex (BMC) of elongating lens fibers at defined points in their migration to the posterior sutures. Methods: Normal, juvenile (4-6 week old) Sprague-Dawley rat lenses (n=46) were utilized. Lenses were either decapsulated to obtain whole mounts of lens capsules or sectioned with a vibrating knife microtome. Sections (100 µm thick) were cut parallel to the equatorial plane, beginning at the posterior pole. On both sections and whole mounts, F-actin was localized using phalloidin-FITC while myosin, cadherins, and β1 integrin were localized using immunofluorescent labeling. Specimens were visualized on a laser scanning confocal microscope. Results: F-actin labeling in the equatorial and peri-sutural regions was predominately localized to the periphery of basal fiber ends (consistent with our prior results). At sutures, labeling for F-actin in the BMC was rearranged into numerous small profiles. Furthermore, labeling intensity for F-actin was increased at sutures. Myosin was present in the BMC in all locations examined as a diffuse plaque at fiber ends. Similarly, β1 integrin was also distributed throughout the BMC within the actin-rich borders in all regions except adjacent to and at the suture branches. In that location immunofluorescence for β1 integrin appeared to be reduced. In the equatorial, lateral-posterior, and peri-sutural regions, cadherin showed strong localization around the periphery of basal fiber ends. However, cadherin labeling was markedly reduced in the BMC as fibers detached from the capsule and abutted to form sutures (i.e. in the sutural region). Cadherin was concentrated along the short faces of elongating fiber mid-segments. Conclusions: It appears that F-actin, cadherin and β1 integrin components of the BMC undergo controlled rearrangements in the final stages of migration and detachment from the capsule.