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M Joseph Costello, Kurt O Gilliland, Ashik Mohamed, Kevin L Schey; The role of autophagy and the nuclear excisosome in organelle degradation in lenses of three primate species. Invest. Ophthalmol. Vis. Sci. 2020;61(7):2299.
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Previously, a chick embryo model was used to describe autophagy of non-nuclear organelles and a new organelle, the nuclear excisosome (NE), to degrade the nuclear envelope during the formation of the lens organelle-free zone (OFZ). Autophagy was found to operate similarly in human lenses and in two primate models but the NE had entirely different features in each species.
Lenses from human donors (n=6, ages 55-70), macaque monkeys (n=8, ages 8-13) and Galago bush baby monkeys (n=3, age 2-6) were fixed in formalin followed by paraformaldehyde, then Vibratome sectioned. Sections were fixed and processed for thin-section transmission electron microscopy (TEM) or stained with fluorescent dyes for Airyscan confocal microscopy. Nuclei were stained with DAPI, actin withAlexa-phalloidin, lectins with WGA and membranes with DiI.
The Galago monkey lenses formed four-membrane organelles in the epithelium from fused mitochondria with collapsed cristae and transferred these to nascent fiber cells where they were stabilized until they were used to contact and degrade the outer nuclear membrane near the OFZ. In human and macaque monkey lenses, no such four-membrane structures were observed in the epithelia or fiber cells. In macaque monkey lenses, mitochondria with modified cristae assisted in complex assemblies near nuclear envelopes that removed membrane components into large multi-layered aggregates suitable for rapid degradation. Human lenses showed clusters of mitochondria and vesicles, especially at the ends of elongated nuclei, that produced numerous multilamellar lipid aggregates. Each species displayed unique structures during the final stages of nuclear breakdown at the OFZ. In all species, released lipid was absorbed into plasma membranes as organelles and the degradation machinery disappeared.
Lenses of higher primates have distinct complex nuclear degradation processes that rapidly degrade nuclei in a few fiber cell layers. Prosimian Galago lenses employ a unique linear structure derived from mitochondria to degrade nuclear envelopes more gradually.
This is a 2020 ARVO Annual Meeting abstract.
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