Zscan4 regulates telomere elongation and genomic stability in ES cells

Zscan4 is shown to be involved in maintaining telomeres in embryonic stem (ES) cells. Only 5% of ES cells express Zscan4 at a given time, but nearly all ES cells activate Zscan4 at least once within nine passages. The transient Zscan4-positive state is associated with rapid telomere extension by telomere recombination and upregulation of meiosis–specific homologous recombination genes. Knocking down Zscan4 shortens telomeres, increases karyotype abnormalities and spontaneous sister chromatid exchange, and slows down cell proliferation until reaching crisis by eight passages.