Zscan4 regulates telomere elongation and genomic stability in ES cells

Abstract

Exceptional genomic stability is one of the hallmarks of mouse embryonic stem (ES) cells. However, the genes contributing to this stability remain obscure. We previously identified Zscan4 as a specific marker for 2-cell embryo and ES cells. Here we show that Zscan4 is involved in telomere maintenance and long-term-genomic stability in 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, which encode proteins that are colocalized with ZSCAN4 on telomeres. Furthermore, Zscan4 knockdown shortens telomeres, increases karyotype abnormalities and spontaneous sister chromatid exchange, and slows down cell proliferation until reaching crisis by eight passages. Together, our data reveal a unique mode of genome maintenance in ES cells.

Cancer cells in epithelial-to-mesenchymal transition and tumor-propagating–cancer stem cells: distinct, overlapping or same populations

“…The fact that the EMT-inducing transcription factor SNAIL uses an histone-specific demethylation to cause one of its major effects, the downregulation of E cadherin, implies relatively long time-scale effects . The maintenance of telomeres in ESCs required telomerase expression only once in nine passages (Zalzman et al, 2010). We have seen that DTP phenotypes switch back to normal after 30 generations.…”

“…The permanence of CSC-TPC properties is questionable. ESCs (embryonic stem cells (ESS)) elongate their telomers once in nine passages, indicating, in this case, a sequential dynamic process (Zalzman et al, 2010). Such a dynamic view applies even to cell lines in culture.…”

Zscan4 promotes genomic stability during reprogramming and dramatically improves the quality of iPS cells as demonstrated by tetraploid complementation

“…We next performed immunofluorescence analyses and found that although the percentage of γ-H2AX-positive cells among cells undergoing reprogramming did not differ between the two groups (37.00% ± 2.96% in OSKM vs 34.19% ± 1.34% in OSKMZ, P = 0.389) ( Figure 2B), γ-H2AX-positive foci were more abundant in OSKM-infected cells than in OSKMZ-infected cells ( Figure 2B). Furthermore, colocalization of γ-H2AX and Trf1, indicative of telomere-induced DNA damage foci [28][29][30], was significantly reduced in OSKMZ-infected cells as compared to OSKM-infected cells ( Figure 2C). Because γ-H2AX is a marker for DSBs [31], we tested general sister chromatid exchange (SCE) [32,33] in reprogramming cells.…”

“…Because Zscan4 expression is associated with the maintenance of genomic stability in ES cells, likely by rapid telomere elongation [28], we speculated that Zscan4 induction might contribute to telomere extension during reprogramming. We examined relative telomere length by quantitative telomere FISH (Q-FISH) [38] in OSKM-and OSKMZ-infected MEFs on days 3 and 6 post-infection.…”

“…Zscan4 gene contains a SCAN domain and four zinc finger domains, and three isoforms (Zscan4c, Zscan4d and Zscan4f) encode full-length open reading frames [23]. Zscan4 is expressed specifically in two-cell embryos [23] and transiently in ES cells [28], and plays important roles in preimplantation embryonic development [23] and in the maintenance of genomic stability in ES cells [28]. γ-H2AX was detected in reprogramming cells two days after MEFs were transduced with either OSKM or OSKM plus Zscan4f (OSKMZ) (Figure 2A).…”