Chromosomal instability (CIN) is an important hallmark to oncogenesis and can be diagnosed morphologically by the presence of nuclear anomalies such as micronuclei (MN), nucleoplasmic bridges (NPBs), and nuclear buds (NBuds). We have identified additional nuclear anomalies formed under folate-deficient conditions, defined as "fused" nuclei (FUS), "circular" nuclei (CIR), and "horse-shoe" nuclei (HS) and investigated their suitability for inclusion as additional CIN biomarkers in the lymphocyte cytokinesis-block micronucleus cytome (CBMN-Cyt) assay. Although the morphological appearance of FUS, CIR, and HS suggested an origin from multiple NPB in the fusion region between the two nuclei, the very low frequency of dicentric chromosomes in metaphase spreads from these cultures did not support this model. Fluorescence in situ hybridization (FISH) analysis of cytokinesis-blocked binucleated (BN) cells with peptide nucleic acid probes for telomeres and centromeres (PNA-FISH) revealed a high proportion of fusion regions contained both centromeric and telomeric DNA. This suggests that folate deficiency may disrupt the process of sister chromatid separation and chromosome segregation during mitosis. It was concluded that the FUS, CIR, and HS morphologies represent promising biomarkers of CIN that are sensitive to folate deficiency, and further validation and investigation of the mechanisms responsible for their formation is warranted.
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