title: Superresolution intrinsic fluorescence imaging of chromatin utilizing native, unmodified nucleic acids for contrast.
abstract: Visualizing the nanoscale intracellular structures formed by nucleic acids, such as chromatin, in nonperturbed, structurally and dynamically complex cellular systems, will help expand our understanding of biological processes and open the next frontier for biological discovery. Traditional superresolution techniques to visualize subdiffractional macromolecular structures formed by nucleic acids require exogenous labels that may perturb cell function and change the very molecular processes they intend to study, especially at the extremely high label densities required for superresolution. However, despite tremendous interest and demonstrated need, label-free optical superresolution imaging of nucleotide topology under native nonperturbing conditions has never been possible. Here we investigate a photoswitching process of native nucleotides and present the demonstration of subdiffraction-resolution imaging of cellular structures using intrinsic contrast from unmodified DNA based on the principle of single-molecule photon localization microscopy (PLM). Using DNA-PLM, we achieved nanoscopic imaging of interphase nuclei and mitotic chromosomes, allowing a quantitative analysis of the DNA occupancy level and a subdiffractional analysis of the chromosomal organization. This study may pave a new way for label-free superresolution nanoscopic imaging of macromolecular structures with nucleotide topologies and could contribute to the development of new DNA-based contrast agents for superresolution imaging.
authors.affiliation: Biomedical Engineering Department, Northwestern University, Evanston, IL 60208; Mechanical Engineering Department, Northwestern University, Evanston, IL 60208.
authors.forename: Biqin
authors.initials: B
authors.lastname: Dong
authors.affiliation: Biomedical Engineering Department, Northwestern University, Evanston, IL 60208;
authors.forename: Luay M
authors.initials: LM
authors.lastname: Almassalha
authors.affiliation: Biomedical Engineering Department, Northwestern University, Evanston, IL 60208;
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Stypula-Cyrus
authors.affiliation: Biomedical Engineering Department, Northwestern University, Evanston, IL 60208;
authors.forename: Ben E
authors.initials: BE
authors.lastname: Urban
authors.affiliation: Biomedical Engineering Department, Northwestern University, Evanston, IL 60208;
authors.forename: John E
authors.initials: JE
authors.lastname: Chandler
authors.affiliation: Biomedical Engineering Department, Northwestern University, Evanston, IL 60208;
authors.forename: The-Quyen
authors.initials: TQ
authors.lastname: Nguyen
authors.affiliation: Mechanical Engineering Department, Northwestern University, Evanston, IL 60208.
authors.forename: Cheng
authors.initials: C
authors.lastname: Sun
authors.affiliation: Biomedical Engineering Department, Northwestern University, Evanston, IL 60208; hfzhang@northwestern.edu v-backman@northwestern.edu.
authors.forename: Hao F
authors.initials: HF
authors.lastname: Zhang
authors.affiliation: Biomedical Engineering Department, Northwestern University, Evanston, IL 60208; hfzhang@northwestern.edu v-backman@northwestern.edu.
authors.forename: Vadim
authors.initials: V
authors.lastname: Backman
mesh_terms: D002467:Cell Nucleus / Q000648:ultrastructure*; D002843:Chromatin / Q000648:ultrastructure*; D004247:DNA / Q000737:chemistry; D006367:HeLa Cells; D006801:Humans; D007399:Interphase; D008856:Microscopy, Fluorescence / Q000295:instrumentation / Q000379:methods*; D008938:Mitosis; D009711:Nucleotides / Q000737:chemistry; D061848:Optical Imaging / Q000295:instrumentation / Q000379:methods*; D000072760:Single Molecule Imaging / Q000295:instrumentation / Q000379:methods*
chemical_list: D002843:Chromatin; D009711:Nucleotides; D004247:DNA
keywords: chromatin topology; chromosome; label-free imaging; nucleic acids; superresolution fluorescence microscopy