Comparisons of histones in retinal and brain nuclei from newborn and adult mice

Histone proteins from purified nuclei of neonatal and adult mouse retinas were analyzed and compared utilizing SDS-polyacrylamide gel electrophoresis. Identical procedures were applied to examine the histones extracted from the brains of the same animals. In the newborn and mature retina and brain, 8 histone fractions have been separated, identified and quantified by scanning densitometry. These are the linker histone (H1), consisting of 3 subfractions (H1a, H1b, H1°); the semi-histone uH2A (A24); and the 4 nucleosome core histones (H2A, H2B, H3, H4). Developmental differences are exhibited by the linker histone in both brain and retinal cells. The greatest differences between the histone patterns of retina and brain are also in the H1 group. Because the linker histone is subject to the greatest variability, H1 was selectively extracted with 5% perchloric acid from both neonatal and adult brain. This procedure established that the observed differences are a developmental phenomenon and are not due to interactions of the linker histones with other nuclear proteins. The ratio of the non-histone chromosomal proteins to total histone was found to be significantly greater in both adult and neonatal brain compared to retina at either age.