Mikhail ELTSOV
Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch
Using cryo-electron tomography of vitreous sections, we directly visualized nucleosomes and linker DNA trajectories in situ within flash frozen Drosophila embryos. Measurements of linker length and curvature revealed an irregular zigzag pattern of chromatin folding characterized by relatively limited linker bending. In favorable orientations, individual nucleosome particles and their structural variants could be identified without the need for structural averaging. Moreover, we detected particles containing a variable number of DNA gyres, ranging from fewer than one to up to three, resembling previously proposed non-octameric nucleosome-like particles.
To place these structural observations in the context of functional chromatin organization, we are developing computational approaches for nucleosome identification in cellular tomograms. We believe that our approach, Template Learning, based on training deep-learning networks on synthetic tomographic data, can provide a general framework for detecting small macromolecular complexes in crowded cellular environments.