Abstract
Purpose: :
To evaluate fiber end arrangement both between and within growth shells during the formation of secondary suture branches in a non-primate lens.
Methods: :
Normal (non-cataractous) adult Sprague-Dawley rats (n=12) were utilized. Lenses were examined under a dissecting scope to locate forming suture branches then fixed and vibratome sectioned parallel to the equatorial axis. Sections were labeled with either phalloidin or wheat germ agglutinin conjugated to a fluorescent tag and examined via laser scanning confocal microscopy. Through focus z series’ were utilized to assess fiber organization during the initial stages of suture branch formation.
Results: :
Grossly, secondary suture branch formation was initiated either at proximal ends of primary branches or along their lateral extent. In the latter case, this generally occurred at a preexisting bend. Both F-actin and wheat germ agglutinin effectively delineated fibers along their length and demonstrated the interdigitation of their non-uniform ends at lens sutures. Initiation of suture branches typically involved 16-20 fibers per growth shell and occurred over a depth of 10-12 µm (i.e. corresponding to approximately 5-6 growth shells of fibers). These parameters were consistent for both anterior and posterior suture branch formation. Established branches develop at variable rates of up to 4 µm displacement per growth shell and their elongation also involves rearrangement of fibers from opposing quadrants.
Conclusions: :
In rats, both anterior and posterior secondary suture branches form in a similar (proximal to distal) fashion. This contrasts with primate studies that show distinct anterior-posterior differences in this process. Additionally, the placement of secondary branches in rat lenses is not predictable, leading to the development of variable suture patterns within the model.
Keywords: development • microscopy: confocal/tunneling • immunohistochemistry