Electron Cryo-Ptychography of DNA Organisation Processes

Ptychography is a diffractive imaging technique in which information from overlapping diffraction patterns can be used to solve the phase problem.

This allows for imaging biological samples with much higher contrast and resolution, and recovery of 3D information where TEM would produce a 2D image.

I will develop the technique as a tool for structural biology, particularly in whole-cell imaging where TEM-based tomography would typically be used.

I will use the 3D information recovered by ptychography to virtually divide thick samples into much thinner slices post-imaging, in order to observe small structures which would typically not be visible within the densely crowded environment of the cell, even with state-of-the-art FIB milling techniques.

In particular, I aim to image the cohesin complex, which plays a large role in DNA organisation via a looping mechanism.

The structure of this complex has not been solved in a nuclear environment, as it has not been observed in-vivo, and its interactions with ligands are not fully understood in this context.

This study will help us to understand how cohesin organises DNA through a complex series of interactions with ligands and moderates all genetic processes from transcription to repair.