Proper telomere length is essential for indefinite self-renewal of embryonic stem (ES) cells and cancer cells. Telomerase-deficient late generation mouse ES cells and human ALT cancer cells are able to propagate for numerous passages, suggesting telomerase-independent mechanisms responding for telomere maintenance. However, the underlying mechanisms ensuring the telomere length maintenance are unclear. Here, using late generation telomerase KO (G4 Terc^-/-) ESCs as a model, we show that Zscan4, highly upregulated in G4 Terc^-/- ESCs, is responsible for the prolonged culture of these cells with stably short telomeres. Mechanistically, G4 Terc^-/- ESCs showed reduced levels of DNA methylation and H3K9me3 at Zscan4 promoter and subtelomeres, which relieved the expression of Zscan4. Similarly, human ZSCAN4 was also derepressed by reduced H3K9me3 at its promoter in ALT U2 OS cells, and depletion of ZSCAN4 significantly shortened telomeres. Our results define a similar conserved pathway contributing to the telomere maintenance in telomerase-deficient late generation mESCs and human ALT U2OS cancer cells.

Despite substantial advancements in the field of cryobiology, oocyte and embryo cryopreservation still compromise developmental competence. Furthermore, dimethyl sulfoxide (DMSO), one of the most commonly used cryoprotectants, has been found to exert potent effects on the epigenetic landscape of cultured human cells, as well as mouse oocytes and embryos. Little is known about its impact on human oocytes. Additionally, few studies investigate the effects of DMSO on transposable elements (TE), the control of which is essential for the maintenance of genomic instability. The objective of this study was to investigate the impact of vitrification with DMSO-containing cryoprotectant on the transcriptome, including on TEs, of human oocytes. Twenty-four oocytes at the GV stage were donated by four healthy women undergoing elective oocyte cryopreservation. Oocytes were paired such that half from each patient were vitrified with DMSO-containing cryoprotectant (Vitrified Cohort), while the other half were snap frozen in phosphate buffer, unexposed to DMSO (Non-Vitrified Cohort). All oocytes underwent RNA sequencing via a method with high fidelity for single cell analysis, and which allows for the analysis of TE expression through Switching Mechanism at the 5′-end of the RNA Transcript sequencing 2 (SMARTseq2), followed by functional enrichment analysis. Of the 27,837 genes identified by SMARTseq2, 7331 (26.3%) were differentially expressed (p < 0.05). There was a significant dysregulation of genes involved in chromatin and histone modification. Mitochondrial function, as well as the Wnt, insulin, mTOR, HIPPO, and MAPK signaling pathways were also altered. The expression of TEs was positively correlated with the expression of PIWIL2, DNMT3A, and DNMT3B, and negatively correlated with age. These findings suggest that the current standard process of oocyte vitrification, involving DMSO-containing cryoprotectant, induces significant transcriptome changes, including those involving TEs.

Centrosomal protein 55 (CEP55) has been proposed to have a role in tumor development. However, the expression pattern and clinical relevance of CEP55 has, to the best of our knowledge, not yet been investigated in cervical cancer. The mRNA levels of CEP55 in cervical cancer tissues and paired adjacent non‑cancerous tissues were examined by reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR). The present study assessed the association between immunohistochemical staining of CEP55 and clinicopathological characteristics and survival rates of patients. Compared with the adjacent non‑cancerous tissues, CEP55 expression was significantly increased in cervical tumor tissues, as demonstrated by the results of RT‑qPCR. High expression of CEP55 was significantly associated with lymph node metastasis (P=0.008) and advanced tumor stage (P=0.010). Furthermore, CEP55 overexpression in cervical cancer specimens was significantly associated with poor 5‑year overall and recurrence‑free survival rates (P=0.021 and P=0.010, respectively). The results of multivariate Cox regression analysis revealed that CEP55 expression was a significant, independent predictor for the survival of patients with cervical cancer (hazard ratio=3.057; P=0.035). These data indicated that high CEP55 expression was associated with lymph node metastasis and was an independent predictive factor for an unfavorable prognosis in patients with cervical carcinoma.