Histone proteins in fetal and adult human retinas

The DNA-binding histone proteins from the human retina are described for the first time. Retinas were obtained from male and female donors ranging in age from 11 to 72 years old. Retinas from two human fetuses at approximately four months of gestation were also examined for their histone content. Histones extracted from purified nuclei were separated and analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Eight histone fractions were identified in all retinal samples, and were quantified by scanning transmittance densitometry. These fractions included three subfractions of linker histones (H1a, H1b, H1(0)), four nucleosomal core histones (H2A, H2B, H3, H4), and the modified core histone, A24 (uH2A), comprised of H2A covalently bound to the non-histone protein, ubiquitin. When fetal and adult retinal histones were compared, the relative amounts of the linker histone subfractions proved to be different. In the adult retinas, H1a diminished in amount whereas H1b and H1(0) were increased. No alterations were detected in the core histones. The developmental changes in linker histones may be related to modifications of chromatin compaction which accompany cell differentiation. Species differences in the pattern of linker histones were detected when the nuclear proteins of human and mouse retinas were compared. Non-histone nuclear proteins are more abundant in the adult human retina than in the mouse retina or the fetal human retina.