Imaging evidence revealing stable existence and segregation of doublet structures in double-minute bodies by field emission scanning electron microscopy

Double minutes (DMs) are acentric, telomere-deficient extrachromosomal circular DNA structures that harbor highly amplified oncogenes and drug resistance genes. During interphase, DMs replicate to form paired structures connected by sister chromatids. In anaphase, individual DMs or DM hubs randomly associate with chromosome termini, resulting in unequal segregation between daughter cells. This biased inheritance facilitates the efficient transmission of DMs to progeny, promoting intratumoral genetic heterogeneity and accelerating genome evolution. These processes underscore the functional importance of inter-DMs connections and DMs-chromosomes interactions. However, the structural basis of these interactions remains poorly understood, and their ultrastructural features have yet to be systematically characterized. In this study, we employed high-resolution field-emission scanning electron microscopy (FE-SEM) to investigate the ultrastructural characteristics of DMs in meta-M tumor cells. Specifically, we characterized the surface morphology of single-like DMs (sDMs), diplochromosome-like DMs (dDMs), and sister DMs (sstDMs), and analyzed the fibrous interconnection patterns between sstDMs and the junctional architecture at DMs-chromosomes interfaces. These comprehensive analyses provide ultrastructural evidence essential for understanding the mechanisms of DM inheritance and their biological roles.