Author interview: Hashim is a postdoctoral fellow at JNCASR in Bengaluru, working with Prof. Kaustuv Sanyal. He earned his PhD from The MS University of Baroda under the guidance of the late Dr. Johannes Manjrekar and the late Prof. Bharat B Chattoo. He has expertise in working with S. cerevisiae and various fungal pathogens: Magnaporthe oryzae, Malassezia spp., and Candida albicans. He is currently looking for a faculty position to start his lab. His research specializes in fungal cell biology, the diversity of spindle positioning, and the interactions between organelles.
Lab: Prof. Kaustuv Sanyal, Jawaharlal Nehru Centre for Advanced Scientific Research
Research Summary: We explored a novel role of an autophagy-related protein, Atg11, in the microtubule (MT)-mediated process of chromosome segregation. This study emphasizes the complex interactions between spatially distinct processes within a cell.
What was the core problem you aimed to solve with this research? The effective functioning of various cellular processes relies heavily on communication between organelles, which is facilitated by proteins. In this study, we explored the interplay between two evolutionarily conserved processes: mitosis and autophagy. This stemmed from examining the physical and genetic interactions of proteins involved in mitosis and autophagy. We sought to determine whether autophagy proteins play a role in mitosis, which occurs under nutrient-rich conditions where basal autophagy is also active.
How did you go about solving this problem? We conducted a screening of a series of autophagy deletion mutants and investigated the role of Atg11, one of the proteins associated with autophagy, in mitosis. We employed a multifaceted approach that combined yeast genetics, live-cell microscopy—including single-molecule tracking (SMT) assays—and biochemistry to investigate the role of Atg11 in chromosome segregation. Our research revealed a novel, non-canonical localization of Atg11 at the spindle pole bodies (SPBs), which exhibited dynamic behaviour and were dependent on MTs. We demonstrated that the loss of Atg11 function disrupts the dynamics of both nuclear microtubules (nMTs) and astral microtubules (aMTs), leading to the activation of the spindle assembly checkpoint (SAC) and causing misalignment in spindle positioning, respectively.
How would you explain your research outcomes (Key findings) to the non-scientific community? This story is about two important processes of cell division and autophagy and what brings them together. Our body is made up of millions of cells, which are the smallest units of life. As we grow, cells divide to form two new cells in a process called cell division. Inside each cell, information is stored in DNA, which is copied accurately and split into two identical sets during cell division. The separation of this copied DNA is done with the help of MTs, which are hollow, straw-like structures that help move things inside the cell. This process is important for cell growth, repair, and keeping our genes stable. If there are problems in these processes, it can seriously affect cell survival and may lead to cancer. To prevent this, cells have developed checkpoints to fix any mistakes. Additionally, cells have a way to recycle damaged parts through a process called autophagy, which helps them stay healthy. Both cell division and autophagy require various components to work smoothly. In our research, we show how a protein related to autophagy, called Atg11, not only helps with autophagy but also plays a role in cell division. A pool of Atg11 is located at structures known as microtubule organizing centers (MTOCs), which give rise to microtubules (MTs) and ensure their proper growth and shrinkage. This regulation facilitates the accurate positioning of DNA, allowing for equal separation between the newly formed cells. This study shows how cellular proteins can perform multiple tasks to keep cells healthy.
This landmark study is another testament to provide generous funding for unplanned, curiosity-driven fundamental research activities that often uncover significant hidden facts, otherwise remain unexplored.
What are the potential implications of your findings for the field and society?
This study represents the first report of a novel function for an autophagy-related protein in cell division in budding yeast Saccharomyces cerevisiae. It demonstrates how proteins facilitate intricate communication that is essential for both survival and genome stability under various conditions, including stress. Our research is significant, as it aligns with several other studies that emphasize the relationship between defective spindle alignment, aging, and aneuploidy, which can lead to cancer development and neurodegenerative diseases. Furthermore, our findings underscore the critical role of transient protein-protein interactions in maintaining cellular fitness. We believe that the type of mitosis might be one of the contributing factors influencing the players involved in performing the non-canonical functions of microtubule-dependent high-fidelity chromosome segregation. This study opens up the avenue to explore the pathways for identifying fungal-specific factors that may serve as potential targets for antifungal therapies.
What was the exciting moment during your research? As we explored the role of an autophagy protein in mitosis, we also experienced some exciting moments. The first significant moment occurred when I observed Atg11 dynamically localizing near one of the spindle pole bodies (SPBs) during mitosis. This SPB-proximal localization was notably transient and had not been documented previously. Our findings were further substantiated by bimolecular fluorescence complementation (BiFC) combined with single-molecule tracking (SMT) assays. Additionally, our analysis of Pds1 and Clb4 protein levels through Western blotting reinforced our assertion regarding the activation of the spindle assembly checkpoint (SAC) and the altered dynamics of astral microtubules (aMTs).
Reference: Reza et al., Autophagy-related protein Atg11 is essential for microtubule-mediated chromosome segregation. PLOS Biology 23(4): e3003069. https://doi.org/10.1371/journal.pbio.3003069
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