Internal dynamics of a living cell nucleus investigated by dynamic light scattering.
Recent breakthroughs in cell biology have shown that living cell nucleus is an organized set of distinct domains, each of them having its own role. This organization is highly dynamic. That is, indeed, the key of the cell adaptation to its environment. Therefore, nucleus dynamics reflects the cell state. Although the study of this dynamics has become one of the main stakes of research in cell biology, global dynamics of the nucleus is still badly understood. To investigate this dynamics, we elaborated an original setup to carry out dynamic light scattering experiments. It should be noticed that, if dynamic light scattering is a « classical » technique used to study dynamical properties of organized molecular systems (e.g. colloidal systems, surfactants, polymers in solution, gels, liquid crystals), so far it has never been used to study the dynamical properties of living cell nuclei. By means of this setup, we investigated global dynamics of the nucleus of neuroblastoma cells (SHEP line) during the cell cycle. We observed that the internal dynamics of the nucleus is very rich and complex, with a large range of characteristic times ranging from some milliseconds to decades of seconds. By analyzing the autocorrelation function of the scattered intensity, < I(0)I(t) >, we probed the internal nucleus dynamics accurately from millisecond to second. We point out two independent distributions of characteristic times. The first one is a distribution of fast times ranging from 5 to 70 ms. The second one is a distribution of slow times ranging from 0.5 to 2 s. We shown that these distributions depend on the stage of the cycle in which the cells are. Using this experimental setup, we were also able to point out and investigate a transmission process of apoptotic death from a cell toward its neighbors.