Generation and Characterization of Endonuclease G Null Mice

Abstract

Endonuclease G (endo G) is one of the most abundant nucleases in eukaryotic cells. It is encoded in the nucleus and imported to the mitochondrial intermembrane space. This nuclease is active on single-and double-stranded DNA. We genetically disrupted the endo G gene in mice without disturbing a conserved, overlapping gene of unknown function that is oriented tail to tail with the endo G gene. In these mice, the production of endo G protein is not detected, and the disruption abolishes the nuclease activity of endo G. The absence of endo G has no effect on mitochondrial DNA copy number, structure, or mutation rate over the first five generations. There is also no obvious effect on nuclear DNA degradation in standard apoptosis assays. The endo G null mice are viable and show no age-related or generational abnormalities anatomically or histologically. We infer that this highly conserved protein has no mitochondrial or apoptosis function that can discerned by the assays described here and that it may have a function yet to be determined. The early embryonic lethality of endo G null mice recently reported by others may be due to the disruption of the gene that overlaps the endo G gene.

EndoG is dispensable in embryogenesis and apoptosis

“…Thus, the original description of early embryonic lethality in EndoG knockout mice is due to the inadvertent double gene disruption of EndoG and D2Wsu81e. Our study in conjunction with the recent description of another EndoG null line with no obvious abnormalities 18 substantiates that EndoG is dispensable for normal embryogenesis and normal development.…”

“…Our results, however, are consistent with the observation in this study that EndoG is dispensable for cell death. Furthermore, these results may explain the lack of detectable difference in chromosomal DNA fragmentation between wild-type and EndoG null cells upon apoptotic induction, 18 and similarly, the difference in the kinetics of mitochondrial release of EndoG compared with cytochrome c upon apoptotic induction by proapoptotic Bcl-2 proteins. 21 In C. elegans, knockdown of cps-6 affected DNA fragmentation and appearance of cell corpses during development.…”

“…This is in contrast with a previous report describing embryonic lethality in EndoG null mice, 17 but agrees with a recent report describing viability and lack of obvious abnormalities in EndoG null mice. 18 We extend the latter study by treating mouse embryonic fibroblasts with different cell death stimuli and by subjecting EndoG null mice to excitotoxicity. Fibroblasts generated from the EndoG null mice undergo normal apoptosis to a variety of apoptotic stimuli.…”

Endonuclease G promotes cell death of non-invasive human breast cancer cells

“…It was recently demonstrated that homozygous EndoG−/− knockout mice (129 x C57 background) are not viable, which suggests the great importance of this enzyme for apoptosis during early development [42]. There is a possibility that other factors may affect the role of EndoG in embryogenesis because EndoG−/− knockout mice in C57 background was viable [43]. EndoG has recently been shown to cooperate with DNase I in DNA fragmentation [24].…”

The Drosophila melanogaster Gene cg4930 Encodes a High Affinity Inhibitor for Endonuclease G

“…A role of EndoG in apoptosis is somewhat controversial. EndoG knock-out mice have no defect in apoptotic DNA degradation (16,17), but this might be due to redundancy with CAD and additional nucleases (1,2,18). RNA interference experiments and genetic data in Saccharomyces cerevisiae support a role of EndoG in apoptosis (8,19,20).…”