MBI PhD Oral Defense

Time: 12noon
Date: Tuesday, 26 November 2019
Venue: T-Lab Building, Level 5 Seminar Rooms

Supervisor: Prof. G.V. Shivashankar

Role Of Active Cytoskeletal Forces & Nuclear Lamina In Regulating The Spatiotemporal Chromatin Architecture

by JOKHUN Doorgesh Sharma, Shiva’s Group

Extracellular signals need to be transmitted to the nucleus and chromatin to regulate genomic processes and elicit proper cell response. In addition to signalling pathways, the actin cytoskeleton serves as an important mechanical connection for the propagation of physical signals from outside the cell to the nucleus. While many studies have investigated the role of the actomyosin network in directly transmitting stresses, in this work, we focussed on the intrinsically dynamic nature of the actin cytoskeleton as a means of relaying extracellular signals. We showed that the cytoskeletal network continuously reorganizes and applies dynamic forces on the nucleus even under static extracellular conditions. Further, we used the positional dynamics of telomeres as a handle to sample local chromatin dynamics inside the nucleus. We demonstrated that active cytoskeletal fluctuations feed into the spatiotemporal regulation of chromatin architecture in an extracellular signal-dependent manner. Further, we showed that lamin A/C mechanically couples distal chromatin loci thereby limiting their diffusion characteristics and causing them to exhibit correlated motion. We established that such changes in the translational dynamics of chromatin, more specifically that of telomeric chromatin, impinges upon the binding kinetics of essential chromatin binding proteins. Taken together, our results demonstrate the roles played by the dynamic actin cytoskeleton and nuclear lamina in transmitting extracellular information to the chromatin. In addition, we underscored the link between chromatin organization and cellular state by demonstrating that a multivariate analysis of quantitative nuclear and chromatin architectural features efficiently classifies cells of different types. We further validated the sensitivity of the method by detecting subtle nuclear changes such as those obtained with TNF-α stimulation. Collectively, this thesis establishes chromatin organization as a hub for integrating extracellular signals into genome regulation while concurrently reflecting cellular state. Consequently, quantitative descriptions of chromatin architecture can potentially be exploited as biomarkers for novel image-based diagnostic systems.

**Please note the examination following the seminar is closed-door**