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

Lens fiber differentiation correlated with activation of two different DNAases in lens embryonic cells

In order to identify the different DNAases present in the lens differentiating tissue, we have used an assay which reveals their activity directly on DNA-containing gels after SDS polyacrylamide gel electrophoresis. DNAase renaturation from nuclear embryonic lens extracts does not occur after separation in 0.1% SDS polyacrylamide gel electrophoresis in contrast to that observed with purified micrococcal nuclease. When the SDS concentration in the running buffer and separating gel is decreased to 0.075%, renaturation of lens DNAase and enzyme activities are observed. Isoelectrofocusing was carried out in a polyacrylamide gel which was overlaid with an agarose gel containing DNA, permitting the visualization of the pI of DNAase activity. The presence of several DNAase isoenzymes was demonstrated in 11-day embryonic lenses. In epithelial lens nuclei, high molecular weight (MW) isoenzymes with basic pI were predominant. In post-mitotic fiber lens nuclei, two lower MW isoenzymes with acidic pI were detected as well as high MW activity with a basic pI.

Increased sensitivity of various genes to endogenous DNase activity in terminal differentiating chick lens fibers

In the lens, epithelial cells from the equatorial zone differentiate into postmitotic elongated fibers. One aspect of this differentiation is nuclear shape transformation and DNA degradation. This process is controlled by DNase activity which in fiber nuclei increases with development. DNase activity is also present in the epithelial cell nuclei which appears to be non-functional but could be activated in vitro by exogenous addition of Ca2+. We have analyzed the possible selective action of endogenous DNase on 3 genes involved in lens terminal differentiation, namely delta-crystallin, beta-tubulin and vimentin, and on 1 gene not thought to participate in this process, ovalbumin. We have compared restriction DNA patterns of these genes in nuclei isolated from 11-day-old chick embryos and incubated in Ca2+-free medium or in fresh epithelial and fiber lens tissue at 11 and 18 days of development. During incubation in vitro of 11-day fiber nuclei, there is a net increase in the sensitivity of the delta-crystallin, beta-tubulin, ovalbumin and vimentin chromatin to the endogenous DNase. The vimentin gene appears to be more stable than the beta-tubulin and delta-crystallin genes indicating a degree of specificity of the endogenous DNase activity. In the epithelial nuclei, the lens-specific genes appear to be more stable but paradoxically there is a net degradation of the ovalbumin gene. In freshly isolated tissues the 4 genes were detected in epithelial and fiber cells at 11 and 18 days. Furthermore, in the mature fibers in which the nuclei were degenerating, the latter genes were still not completely digested.