The largest known genomes are encoded by the histoneless liquid crystalline chromosomes (LCCs) of dinoflagellates. LCC represents a good model for studying higher-order structure of chromosome and the interactions of chromosomal DNA condensation. In the present study, the nuclear decondensation was investigated in response to extranuclear EDTA chelation. Optical microscopy identified several decondensation states of the LCCs with various EDTA concentrations. The dynamic decondensation processes were found to be in a nonlinear manner. The thermal stability assessment of condensed and EDTA-treated isolated nuclei revealed a thermal transition at 64 ℃ corresponding to liquid crystalline phase transition of LCCs. AFM and electron microscopy showed the presence of Large Nucleosome-L...[ Read more ]

The largest known genomes are encoded by the histoneless liquid crystalline chromosomes (LCCs) of dinoflagellates. LCC represents a good model for studying higher-order structure of chromosome and the interactions of chromosomal DNA condensation. In the present study, the nuclear decondensation was investigated in response to extranuclear EDTA chelation. Optical microscopy identified several decondensation states of the LCCs with various EDTA concentrations. The dynamic decondensation processes were found to be in a nonlinear manner. The thermal stability assessment of condensed and EDTA-treated isolated nuclei revealed a thermal transition at 64 ℃ corresponding to liquid crystalline phase transition of LCCs. AFM and electron microscopy showed the presence of Large Nucleosome-Like Domains in LCCs with the diameter about 80 nm. This size of nucleosome-like domains is close to the minimum theoretical organelle size, as predicted by the ‘A-O’ theory, that will generate sufficient entropy-driven depletion forces to condensation. We propose that entropy-driven depletion forces and counterionic attractions of divalent cation cooperatively modulate nucleosome-like fundamental units for stabilization and assembly to higher-order structure of liquid crystalline chromosomes of dinoflagellates.

The study of DNA condensation by dinoflagellate histone-like protein HCc3p demonstrated that the cholesteric liquid crystalline DNA can be formed by the interaction of DNA and HCc3p in vitro. The dynamic DNA-HCc3p interactions were studied by CD spectroscopy and ITC. The results suggest that the homogenously formation of cholesteric liquid crystalline DNA-HCc3p condensate involved two stage process, first by entropy-driven counterionic attraction, and followed by intermolecular electrostatic-driven assemble of bundle-like DNA-HCc3p complexes assembly when DNA charges were neutralized. The DNA charge inversion is also observed in electrophoretic mobility assays, which indirectly support the electrostatic interactions role in HCc3p induced LC DNA formation.

The quantitative imaging techniques of Metripol and Synchrotron hard X-ray Zernike phase contrast tomography were also discussed for imaging intranuclear liquid crystalline chromosomes.