Each organelle has a very distinct structure depending on the functions it supports. The endoplasmic reticulum (ER) is a highly dynamic network of nuclear envelope and peripheral sheets and tubules. Many structural determinants of the ER network formation and maintenance have been described; however, it is not yet understood how the functional subdomains are formed and maintained, or how the ER is constantly rearranging. Our aim is to elucidate factors that generate and maintain the intricate balance of structure and dynamics underlying the functional efficacy of the ER.
The endoplasmic reticulum has a key role in coordinating several critical homeostatic mechanisms for lipid and protein biosynthesis, and constitutes a reservoir of Ca2+ -ions that act as signalling molecules to regulate many essential cellular processes. To accommodate the vast range of functions, ER network spreads throughout the cell, and distributes its functions into structural subdomains according to their specific needs.
We are studying mechanisms that control ER structural balance and dynamics, and aim to identify factors involved in stabilization of flat membranes of sheets and creation of membrane curvature supporting ER tubule formation and maintenance. Knowledge of the mechanisms behind the structural maintenance of the ER will be the key towards deeper understanding of its functions and their regulation. Moreover, the identification of proteins and forces that maintain ER morphology will been essential in understanding the connection between many diseases, such as Alzheimer's disease and Hereditary spastic paraplegia, and the ER.
The ER network is highly dynamic, undergoing continuous morphological rearrangements, extensions and movements. The cell modulates ER dynamics during different phases of its development and division, in effect, modulating the ER functions in tune with its requirements.
Our morphological analysis revealed that ER network organization, sheet-to-tubule ratio, and sheet morphology vary greatly between different cell lines. Progressive sheet-to-tubule transformation is a general mechanism for ER partitioning during cell division and correlates with ribosome density. Recently, we have identified the specific factors required for generating the high curvature morphology of mitotic ER.
Aberrant expression of many ER membrane proteins have been linked to major debilitating neurodegenerative disorders. We are interested in understanding the specific mechanism of their action and regulation during cell development and division.
In addition to vesicular transport, where vesicles pinch off from the donor membrane and then fuse with the acceptor membrane releasing the luminal content, the ER communicates with other organelles such as mitochondria, endo/lysosomes, lipid droplets, and plasma membrane via membrane contacts. Membrane contacts do not lead to fusion of membranes and mixing of luminal contents, but allow cross talk between adjacent membrane bilayers. Here, various protein complexes can work in concert to perform specialized functions such as binding, sensing and transferring molecules, as well as engaging in organelle biogenesis and dynamics. The continuity of the ER network and the extensive contacts that it makes with other organelles provides a mechanism to propagate various signals throughout the cell.
We are analyzing the morphology of the organelle contacts under different physiological conditions and in cells with altered ER sheet-tubule balance. Understanding such contact regions is indispensable, as they are significant for basic cellular functions and their alterations may trigger onset and progression of anomalous conditions including cancer.
Understanding the structure-function relations of cells and cellular organelles in their natural context requires multidimensional imaging. The large image datasets thus generated need to be processed, visualized and analyzed effectively.
Microscopy Image Browser (MIB) is a high-performance Matlab-based software package developed in our lab. It enables advanced image processing, segmentation and visualization of multi-dimensional (2D-4D) light and electron microscopy datasets.
MIB facilitates full utilization of acquired data including quantitative analysis of morphological features. Its open-source environment enables fine-tuning and possibility of adding new plug-ins to customize the program for specific needs of any research project. For example, we have developed special plug-ins for the Microscopy Image Browser software to measure the quantity and length of the contacts between ER and other organelles such as mitochondria and lipid droplets.