Morphology and organization of posterior fiber ends during migration

To characterize structural parameters of the basal membrane complex (BMC) and to determine the arrangement and organization of posterior fiber ends during elongation/migration in lenses with branched sutures.

Lenses from normal, juvenile (4-6 week old) Sprague-Dawley rats (n=16) were utilized. Posterior fiber ends were assessed on both whole mounts of lens capsules and on decapsulated lenses. The size, shape and organization of migrating fiber ends was assessed by scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM) along the entire posterior surface. The area of the BMC was measured using image analysis software and subjected to statistical analysis.

Posterior fiber ends had a characteristic regional arrangement during elongation and migration along the capsule. These regions were termed the equatorial, the lateral-posterior (posterior from the equator to within 150 microm of the sutures), the peri-sutural (150 microm surrounding the sutures), and the sutural. The area of fiber ends (seen by SEM) was compared to the area of fluorescent F-actin profiles (seen by LSCM). There was no significant difference (p=0.324) between the average basal end area (40.21 microm2) and the average area of F-actin profiles (40.65 microm2). The average fiber end area in the lateral-posterior, peri-sutural, and sutural regions was 63.19 microm2, 71.95 microm2, and 25.75 microm2, respectively. In the equatorial region, footprints were aligned in rows oriented toward the posterior pole, consistent with the arrangement of straight, meridional rows. Initially, fiber ends within the lateral-posterior region were arranged in short irregular rows having variable orientation with respect to the posterior pole. The remainder of these ends were randomly arranged. In the peri-sutural region, fiber ends approaching suture branches were aligned in short rows oriented at angles to the posterior pole. At the sutures, fiber ends appeared to become rounded, presumably during detachment from the capsule.

The results confirm that F-actin profiles delineate the BMC of posterior fiber ends. Furthermore, the average area, shape and arrangement of fiber ends varies in a predictable pattern during migration. The data suggests that elongating fiber ends follow defined migration patterns along the posterior capsule to their sutural destinations. This controlled process is crucial to the formation of ordered suture patterns, thereby minimizing their adverse effects on lens optical quality.