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S. T. Donohue, K. J. Al-Ghoul; The Initiation of Suture Branch Formation in Rat Lenses. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2799.
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To evaluate fiber end arrangement both between and within growth shells during the formation of secondary suture branches in a non-primate lens.
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.
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.
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.
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