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M Joseph Costello, Ashik Mohamed, Kurt O Gilliland, Jamie L Wenke, Kevin L Schey; Quantitative morphology of the remodeling zone in non-human primate lenses. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2632.
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© ARVO (1962-2015); The Authors (2016-present)
During fiber cell differentiation, a unique remodeling zone (RZ), first identified (Lim et al., 2009) in human lenses over a wide age range, consistently occurred at about 100 µm from the lens surface with a very narrow width of about 40 µm. It was noted in a TEM analysis (Costello et al., 2013) that interdigitations similar to ball-and-sockets (BS) appeared at high frequency just prior to the RZ. It was reported in 2014 (Costello et al., IOVS 55, E-Abstract 733) that non-human primate lenses displayed a similar RZ with increased numbers of BS interdigitations. The goal of the present study is to quantify the changes in BS density as a function of depth from the capsule to determine the precise location and width of the RZ.
Macaque monkey lenses (8-13y, n = 5) were fixed in 10% buffered formalin for 24-48h followed by fixation in 4% paraformaldehyde in cacodylate buffer for 48h. Fixed lenses were Vibratome sectioned into 200 µm thick slices and further processed for transmission electron microscopy as described previously. Areas about 14 µm2 were imaged at 4,400x from the capsule to a depth about 200 µm; morphological features were identified for each image and modeled with statistical algorithms in Origin v. 7.0.
Thin sections of well-preserved regions near the equatorial plane showed a gradual loss of autophagic vesicles and a rapid increase in BS at about 80 µm from the capsule where fiber cells still had classical flattened hexagonal cross-sections. The BS were typically teardrop shaped with a narrow neck (about 0.2 µm wide and 0.5µm long), smooth surface membrane and dense cytoplasm. By 140 µm depth, nearly all the BS had been transformed into irregular intercellular projections with variable sizes, angular membranes and smooth internal cytoplasm nearly identical to the adjacent cytoplasm. The appearance and remodeling of the BS fit very well to a Gaussian plot, the width of the plot being a good measure of the RZ. Although there were small variations in location and width of the RZ, all lenses displayed similar behavior. These changes in membrane topology precede the formation of undulating membranes, which characterize fiber cells at depths greater than about 200 µm.
The dramatic changes of fiber cell morphology in the region about 80-140 µm from the surface suggest that RZ formation is a highly regulated and consistent component of fiber cell differentiation in primate lenses.
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