Live Cell Imaging in Fission Yeast

Conserved Phosphorylation of the Myosin1e TH1 Domain Impacts Membrane Association and Function in Yeast and Worms

Cells have an intrinsic ability to rapidly respond to environmental change to regulate cell cycle progression and membrane organisation, thereby affecting cell growth and division. The actin cytoskeleton is a highly dynamic complex of proteins that can rapidly reorganise to change the growth pattern of a cell. Class I myosins are monomeric actin-associated motor proteins that play key roles in diverse cellular functions such as tension sensing and membrane reorganisation, as well as promoting actin polymer nucleation at sites of cell growth. We have analysed the localisation and function of both C. elegans class 1 myosins, HUM-1 (Myo1e) and HUM-5 (Myo1d). Both motors are non-essential. While HUM-1 is expressed in diverse cells and tissues, HUM-5 localises exclusively to a subset of cells in the nervous system. While animals lacking hum-1 displayed a reduced maximal brood size and a delay in embryo release, deleting both hum-1 and hum-5 together shortened C. elegans lifespan. Moreover, we identified that phosphorylation of a conserved serine residue within the Myo1e TH1 domain had an impact on the localisation and function of the motor protein in both C. elegans and the fission yeast, S. pombe, indicating this modification modulates the ability of Myo1e/HUM-1 to interact with phospholipids at the plasma membrane. We conclude that TH1 domain phosphorylation plays a key role in regulating the cellular distribution and function of Myo1e motors across all eukaryotes.

High-yield vesicle-packaged recombinant protein production from E. coli

We describe an innovative system that exports diverse recombinant proteins in membrane-bound vesicles from E. coli. These recombinant vesicles compartmentalize proteins within a micro-environment that enables production of otherwise challenging insoluble, toxic, or disulfide-bond containing proteins from bacteria. The release of vesicle-packaged proteins supports isolation from the culture and allows long-term storage of active protein. This technology results in high yields of vesicle-packaged, functional proteins for efficient downstream processing for a wide range of applications from discovery science to applied biotechnology and medicine.

Fluorescence and phosphorescence lifetime imaging reveals a significant cell nuclear viscosity and refractive index changes upon DNA damage

Cytoplasmic viscosity is a crucial parameter in determining rates of diffusion-limited reactions. Changes in viscosity are associated with several diseases, whilst nuclear viscosity determines gene integrity, regulation and expression. Yet how drugs including DNA-damaging agents affect viscosity is unknown. We demonstrate the use of a platinum complex, Pt[L]Cl, that localizes efficiently mostly in the nucleus as a probe for nuclear viscosity. The phosphorescence lifetime of Pt[L]Cl is sensitive to viscosity and provides an excellent tool to investigate the impact of DNA damage. We show using Fluorescence Lifetime Imaging (FLIM) that the lifetime of both green and red fluorescent proteins (FP) are also sensitive to changes in cellular viscosity and refractive index. However, Pt[L]Cl proved to be a more sensitive viscosity probe, by virtue of microsecond phosphorescence lifetime versus nanosecond fluorescence lifetime of FP, hence greater sensitivity to bimolecular reactions. DNA damage was inflicted by either a two-photon excitation, one-photon excitation microbeam and X-rays. DNA damage of live cells causes significant increase in the lifetime of either Pt[L]Cl (HeLa cells, 12.5-14.1 µs) or intracellularly expressed mCherry (HEK293 cells, 1.54-1.67 ns), but a decrease in fluorescence lifetime of GFP from 2.65 to 2.29 ns (in V15B cells). These values represent a viscosity change from 8.59 to 20.56 cP as well as significant changes in the refractive index (RI), according to independent calibration. Interestingly DNA damage localized to a submicron region following a laser microbeam induction showed a whole cell viscosity change, with those in the nucleus being greater than the cytoplasm. We also found evidence of a by-stander effect, whereby adjacent un-irradiated cells also showed nuclear viscosity change. Finally, an increase in viscosity following DNA damage was also observed in bacterial cells with an over-expressed mNeonGreen FP, evidenced by the change in its lifetime from 2.8 to 2.4 ns.

Introduction to Fission Yeast as a Model System

Here, we briefly outline the history of fission yeast, its life cycle, and aspects of its biology that make it a useful model organism for studying problems of eukaryotic molecular and cell biology.