Endogenous nuclease activity in chick embryo lens cells

DNase activity in murine lenses: implications for cataractogenesis

In murine lens extracts a Mg(2+)-dependent DNase activity was found and characterized with respect to its ionic conditions. The lenticular DNase can be clearly distinguished from DNaseII. Only a moderate DNase activity is detectable in intact nuclei of lens cells from 1-day-old mice, but DNase is obviously present with high activity in lens cell nuclei from 7-day-old mice. During this time, when murine eyes are not yet open, and the fiber cell nuclei including the nuclear membrane remain to be completely digested, only weak activity can be detected in cytosolic lens extracts. In three allelic dominant mice mutants exhibiting hereditary cataracts the DNase activity is inhibited. The decrease of DNase activity follows the same directionality (Cat-2ns > Cat-2no > Cat-2t) as the decrease in the relative content of water soluble lens proteins, which might be used as a rough indicator for the severity of cataractogenesis. Both trends are highly significant (P < 0.0001).

Ca2+, Mg2+-dependent endonuclease activity in different subpopulations of spleen cells from normal and erythroleukemic mice

We have detected Ca2+, Mg2+-dependent endonuclease activity in spleen cells of normal, Friend erythroleukemic, and phenylhydrazine-treated mice. When nuclei were isolated and incubated in the presence of Ca2+ and Mg2+ ions, the activity resulted in the production of 3'-OH termini in the cellular DNA and the release of chromatin due to internucleosomal DNA fragmentation. This enzyme activity was chromatin-bound and could be extracted from chromatin in an active form in 0.35 M KCl. The majority of endonuclease activity from erythroleukemic spleens was present in nuclei of precursor erythroid cells of low buoyant density (1.025-1.05 g/ml). Uninfected normal splenic tissue contained an endonuclease activity which was almost entirely confined to a B-lymphocyte population of high buoyant density (greater than 1.07 g/ml). Erythroid cell-enriched spleens from phenylhydrazine-treated mice exhibited a distribution of endonuclease activity in cells at low and high densities reflecting a mixture of erythroid and lymphoid cells. Cloned erythroleukemic cell lines propagated in vitro lacked cells of low density and showed no detectable endonuclease activity. However, nuclei from these cell lines were susceptible to exogenously added endonuclease extracted from erythroleukemic spleen cells. These same cell lines propagated as subcutaneous tumors contained endonuclease activity and a morphologically-similar low-density cell population which accounted for the endonuclease activity in these tumors. Nuclei from cloned lymphoid cell lines, representing different B-lymphocyte phenotypes, showed differences in the presence of endonuclease activity. Among the cell lines tested, only those expressing late B-cell markers showed detectable endonuclease activity.