Figure 1: Super-resolution image of a nuclear pore labelled with an antibody against one protein component of the NPC (Nup160). An image is gradually built up by localising the centers of individual fluorophores switching between light-emitting and dark state (Szymborska A, et al., 2013).
The Ellenberg group studies how cells divide and organise in mitosis and meiosis, where errors can lead to problems such as cancer and infertility.
Previous and current research
The genome of eukaryotic cells is compartmentalised inside the nucleus, delimited by the nuclear envelope whose double membrane is continuous with the endoplasmic reticulum and perforated by nuclear pore complexes. In M-phase, most metazoan cells reversibly disassemble the nucleus. Chromosomes are condensed, attached to cytoplasmic spindle microtubules, faithfully segregated and decondensed, and the nucleus rapidly reassembles. Errors in this beautifully orchestrated cycle of cell division can lead to severe consequences, such as cancer in somatic cells and infertility in gametes.
Our overall goal is to systematically elucidate the mechanisms underlying cell division and nuclear organisation. We are developing a broad range of advanced fluorescence-based imaging technologies to assay the functions of the involved molecular machinery non-invasively, automate imaging to address all its molecular components, and computationally process image data to extract biochemical and biophysical parameters. Our research focuses on three areas: systems biology of mitosis, nuclear structure, and molecular mechanisms of meiosis and early embryonic mitosis.
We have previously identified hundreds of new cell division genes by RNAi-based screening of the entire human genome and are now studying in live cells – in high throughput – protein function, protein-protein interactions and protein networks during somatic mitosis by automating advanced fluorescence imaging and single molecule techniques, such as fluorescence (cross) correlation spectroscopy.
We also recently determined the positions of various nuclear pore complex (NPC) components and directly resolved the ring-like structure of the NPC by light microscopy, combining stochastic super-resolution microscopy (SRM) with single particle averaging (figure 1). Currently we elucidate the assembly mechanism of the NPC and chromatin dynamics over the cell cycle.
By complete kinetochore tracking we demonstrated that meiotic spindle assembly and asymmetric positioning rely on novel mechanisms and that meiotic chromosome biorientation is highly error prone. We are now developing gentle light-sheet-based imaging systems for high-throughput imaging of mouse oocytes and embryos to allow systematic molecular analysis of meiosis and early embryonic mitosis.
Figure 2: A 3D metaphase model reconstructed from confocal images of HeLa cells. The colours identify different elements / proteins important for mitosis (centrosome, cyan; chromatin, green; kinetochores / centromeres, red).
Future projects and goals
We want to gain comprehensive mechanistic insight into the division of human mitotic cells, provide a biophysical basis to understand nuclear organisation, and establish methods for systems analysis of the meiotic and first mitotic divisions of mammalian oocytes and embryos.
For a systems-level understanding of all crucial protein interactions during cell division, we will combine automated bulk as well as single molecule imaging and computational data analysis with advanced machine learning and modelling approaches to integrate all interactions into one canonical 4D model of a human dividing cell (figure 2).
To come to a structural understanding of nuclear organisation, we will explore and further improve correlative imaging approaches combining live cell confocal microscopy, SRM and electron tomography to unravel the mechanism of NPC assembly and disassembly as well as the human genome architecture and chromatin organisation and compaction.
To be able to apply systems biology tools to oocyte meiosis and early embryonic mitosis, we will push light-sheet-based imaging technology development further to improve its light efficiency and resolution to establish a physiological molecular model for early mammalian development and infertility.