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M. Lucey, K. West, M. Bustin, M.K. Duncan; The Expression of HMGNs During Ocular Development . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1876.
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Purpose: The HMGN proteins are a group of non–histone nuclear proteins that associate with the core nucleosome at the level of chromatin. They disrupt the interaction of DNA from the core nucleosome and H1 in a dynamic manner to loosen compaction of the chromatin fiber. While HMGN1 and HMGN2 have been reported to be ubiquitously expressed, HMGN3 is more tissue specific, with highest levels in the eye and brain. This study investigates the expression pattern of HMGN1, HMGN2, and HMGN3 during ocular development Methods: The distribution of HMGN family members was investigated in developing mouse eyes using immunohisochemistry. The ratio of HMGN3a and HMGN3b in various tissues of the eye was also examined using RT–PCR and western blot analysis. An antibody against chicken HMGN3 was also developed in rabbits to continue studies in the lens cells of chickens Results: HMGN1 expression appears to be present at some level in all of the various tissues of the eye. However, highest expression was found in cells undergoing proliferation, with reduced levels in cells that were differentiated. HMGN2 was found to be present at relatively high levels in all cells and tissues. HMGN3 is present at low levels in undifferentiated neural precursors of the retina but upregulates as these cells exhibit morphological differentiation, but decreases in photoreceptors in the adult. In the lens, HMGN3 is present at only low levels in the epithelium but its levels upregulate markedly in the transition zone and fiber cells of the lens. In the cornea, HMGN3 is first seen in the presumptive corneal epithelium but not the migratory neural crest. As the corneal stroma and endothelium begin to differentiate, HMGN3 expression becomes prominent but then is downregulated in the adult although appreciable HMGN3 protein is detected in the adult corneal epithelium. Conclusions: It is possible that HMGN1 is involved in regulating chromatin in areas where there are genes essential for maintaining proliferation, where HMGN3 may then take over and open up the chromatin in areas with genes that help in cell differentiation. Since HMGN2 is expressed in both proliferating and differentiating cells, it may regulate an entirely different set of genes, or keep the chromatin structure in a dynamic state that allows access for a more general set of transcription factors.
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