Nonlinear polarimetric analysis of DNA liquid crystalline domains

In nuclei of eukaryotic cells, DNA molecules are tightly packed up to a concentration level of several hundreds of mg/ml. At high concentration, in order to decrease the intermolecular volume the DNA strands self- organize and form domains containing molecules oriented along preferential directions. These self-organizing properties give rise to various liquid crystalline phases, similar to the process of physiologic DNA condensation. Liquid crystalline phases were observed in concentrated DNA solutions, but also in nucleosome-like particles or plasmids solutions. Besides their biologic implication, these self-organized structures may serve as a simple model for the structural study of DNA higher order organization schemes and as a first approach mimicking the complex chromatin topology. This study shows the potential of non-linear polarimetry as a useful tool for structural analysis of highly organized condensed DNA phases. This microscopy method can be further applied to more complex ordered biologic structures such as nucleosome-like particles or chromatin. The aim of this work is to investigate the polarization-sensitive two-photon fluorescence analysis of DNA liquid crystalline domains doped with two well known dyes, Propidium Iodide (PI) and Hoechst.