PML nuclear bodies in 3D
Promyelocytic leukemia nuclear bodies (PML-NBs) are functionally heterogeneous structures involved in diverse nuclear functions like tumor suppression, telomere elongation and apoptosis. They exert their activit by dynamically concentrating numerous different proteins within the PML-NB subcompartment — but how does PML-NB structure enable them to act as assembly platforms for the various factors? Together with our collaboration partners we have investigated this issue by combining high-resolution techniques of 4Pi and correlative electron microscopy. By imaging PML and Sp100 proteins (both integral to PML-NB structure) and their relative localisation to small ubiquitin-related modifier 1 (SUMO-1), SUMO2/3, heterochromatin protein 1 (HP1) and telomeres the structure of PML-NBs was elucidated. Based on our results we propose a model to explain how various activities can be concentrated in PML-NBs in a dynamic manner. The conjugation of PML and Sp100 proteins to SUMO-1 results in their self-assembly into a spherical shell of 50-100 nm thickness and variable diameter. By contrast, SUMO2/3 is found mainly in the interior of a subset of PML-NBs, where it might control the protein composition and therefore function of these PML-NBs.
Lang, M., Jegou, T., Chung, I., Richter, K., Udvarhelyi, A., Münch, S., Cremer, C., Hemmerich, P., Engelhardt, J., Hell, S. W. & Rippe, K. (2010). Three-dimensional organization of PML nuclear bodies, J. Cell Science 123, 392-400. Abstract | Reprint (4.3 MB pdf file)