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Xiaohua Gong, Catherine Cheng, Wiktor Stopka, Jing Zeng, Chun-hong Xia; Lens fiber cell denucleation and cataractogenesis. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1687.
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To investigate the mechanisms that control nuclei distribution, chromatin behavior or denucleation process during lens fiber cell differentiation and maturation in normal and cataractous mice caused by various mutations, such as alpha-crystallin gene mutations, intermediate filament protein CP49 gene deletion and connexin gene knockouts. Moreover, to evaluate how aging affects fiber cell differentiation and maturation.
Transgenic expression of histone 2B (H2B)-GFP and DNA-staining dyes were used to monitor the distribution and disassembly of fiber cell nuclei and chromatin behavior in live lenses by 3-dimensional confocal laser microscopic imaging. Western blotting and immunostaining were performed to elucidate the molecular and cellular changes.
Distinct nuclei distribution was observed along the anterior and posterior equatorial panel during fiber cell differentiation and elongation. Chromatins in fiber cell nuclei displayed sequential changes during fiber cell maturation. All inner fiber cells lost their nuclei at about 150 μm distance from the lens surface. However, denucleation of fiber cells often occurred long before reaching the nuclei-free zone. During denucleation, H2B-GFP proteins were diffused along both anterior and posterior directions and then were evenly distributed with cell boundaries of inner fibers. Altered distribution of fiber cell nuclei and aberrant distribution and/or aggregation of the H2B-GFP proteins were detected in different cataractous lenses. In addition, aberrant aggregation of H2B-GFP proteins was also detected in newly formed cortical mature fiber cells in aged wild-type lenses.
This work reveals that inner fiber cell denucleation occurs at around 100-150 μm distance from the lens surface rather than an old assumption that fiber cell denucleation proceeds only in several cell layers before the nuclei-free zone. Aging impairs fiber cells denucleation by blocking the disassembly of nuclear proteins and induces the aggregation of nuclear proteins such as H2B. Different types of cataracts caused by various gene mutations are associated with uniquely altered distribution and/or disassembly of fiber cell nuclei. Coordinated functions of intercellular gap junction communication, intermediate filaments and alpha-crystallin chaperons precisely regulate the distribution and disassembly of fiber cell nuclei during cell maturation.
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