Changes in the shape of the cell nucleus have long been used to diagnose cancer from biopsies and are associated with a large group of human genetic diseases, called laminopathies. Recently, our lab and others discovered that these morphology changes can be correlated with an even more extreme phenomenon: nucleus rupture. During nucleus rupture, critical nuclear functions are impaired and the DNA is exposed to a damaging cellular environment. Amazingly, nuclei can repair after these events and the cells continue to proliferate. However, our work demonstrated that when small nuclei, called micronuclei, form after replication stress or defective cell division, they rupture at a high frequency and cannot repair. This leads to massive changes in the structure of the DNA that occur frequently in many types of cancer. In addition, rupture in micronuclei and nuclei can induce inflammation and increase cell invasion. My lab is focused on understanding why nuclear rupture occurs, why these ruptures are only sometimes repaired, and how nucleus rupture affects gene expression and cell behavior in cancer. This talk will encompass the work we have done on nucleus rupture and a new connection between histone modifications and the structure and stability of the micronuclear envelope.
Mechanical forces play a key role in biological processes such as cell migration, cell division, and enzyme activity. In recent years molecular force sensors have been developed as tools for in situ and in vivo force measurements. In this work we focus on using all-atom steered molecular dynamics simulations to study the relation between design parameters and mechanical properties for three types of molecular force sensors commonly used in cellular biological research: two amino acid-based sensors and one DNA-based sensor. The amino acid-based sensors consist of a pair of fluorescent proteins, which can undergo Förster resonance energy transfer (FRET), linked by a spider silk (GPGGA)n or synthetic (GGSGGS)n disordered region. The DNA based sensors - consisting of two strands of DNA that can be unzipped or sheared upon force application, also have fluorophores for FRET readout of dissociation. We simulated nine sensor constructs, three of each kind, to study the relation between design parameters and mechanical behavior. The constructs were equilibrated for 10 to 15 nanoseconds before applying force. The flexible peptide linkers were stretched by applying forces to their N- and C-terminal Cα atoms in opposite directions. Similarly, we equilibrated the DNA-based sensor and pulled on the phosphate atom of the terminal guanine of one strand and a selected phosphate atom on the other strand to pull in the opposite direction. These simulations were performed at constant velocity (0.01 nm/ns - 10 nm/ns) and constant force (10 pN – 500 pN) for all versions of the sensors including different linker sizes for the peptide-based sensors and different pulling locations for the DNA-based sensor. Our results show how the elastic response of these sensors depends on their length, sequence, secondary structure, loading rate, and force. Mechanistic insights gained from simulations analyses suggest optimal fluorophore choice and can help interpret experimental results and facilitate the rational design of new sensors for use in DNA, protein and hybrid molecular devices with desired force sensitivity.
Last update: 11/27/2023, Ralf Bundschuh