Articles by Janet Sheung in JoVE
Visualizing Cytoplasmic Flow During Single-cell Wound Healing in Stentor coeruleus Mark Slabodnick1,2, Bram Prevo1,3, Peter Gross1,4, Janet Sheung1,5, Wallace Marshall1,2 1Physiology Course, Marine Biological Laboratory, 2Department of Biochemistry & Biophysics, University of California San Francisco, 3Department of Physics and Astronomy, Vrije Universiteit Amsterdam, 4Max Planck Institute of Molecular Cell Biology and Genetics, 5Department of Physics, University of Illinois Urbana-Champaign The giant ciliate Stentor coeruleus is a classical system for studying regeneration and wound healing in single cells. By imaging Stentor cells simultaneously at low and high magnification it is possible to measure cytoplasmic flows before, during, and after wounding.
Fluorescence Imaging with One-nanometer Accuracy (FIONA) Yong Wang*1,2, En Cai*1,2, Janet Sheung1,2, Sang Hak Lee1,2, Kai Wen Teng2,3, Paul R. Selvin1,2,3 1Department of Physics, University of Illinois at Urbana-Champaign, 2Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, 3Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign Single fluorophores can be localized with nanometer precision using FIONA. Here a summary of the FIONA technique is reported, and how to carry out FIONA experiments is described.
Other articles by Janet Sheung on PubMed
Fluorescence Imaging with One Nanometer Accuracy: in Vitro and in Vivo Studies of Molecular Motors Methods in Molecular Biology (Clifton, N.J.). 2011 | Pubmed ID: 21809199 Traditional microscopy techniques are limited by the wave-like characteristics of light, which dictate that about 250 nm (or roughly half the wavelength of the light) is the smallest distance by which two identical objects can be separated while still being able to distinguish between them. Since most biological molecules are much smaller than this limit, traditional light microscopes are generally not sufficient for single-molecule biological studies. Fluorescence Imaging with One Nanometer Accuracy (FIONA) is a technique that makes possible localization of an object to approximately one nanometer. The FIONA technique is simple in concept; it is built upon the idea that, if enough photons are collected, one can find the exact center of a fluorophore's emission to within a single nanometer and track its motion with a very high level of precision. The center can be localized to approximately (λ/2)/Ö-N, where λ is the wavelength of the light and N is the number of photons collected. When N = 10,000, FIONA achieves an accuracy of 1-2 nm, assuming the background is sufficiently low. FIONA, thus, works best with the use of high-quality dyes and fluorescence stabilization buffers, sensitive detection methods, and special microscopy techniques to reduce background fluorescence. FIONA is particularly well suited to the study of molecular motors, which are enzymes that couple ATP hydrolysis to conformational change and motion. In this chapter, we discuss the practical application of FIONA to molecular motors or other enzymes in biological systems.
Motor Domain Phosphorylation Modulates Kinesin-1 Transport The Journal of Biological Chemistry. Nov, 2013 | Pubmed ID: 24072715 Disruptions in microtubule motor transport are associated with a variety of neurodegenerative diseases. Post-translational modification of the cargo-binding domain of the light and heavy chains of kinesin has been shown to regulate transport, but less is known about how modifications of the motor domain affect transport. Here we report on the effects of phosphorylation of a mammalian kinesin motor domain by the kinase JNK3 at a conserved serine residue (Ser-175 in the B isoform and Ser-176 in the A and C isoforms). Phosphorylation of this residue has been implicated in Huntington disease, but the mechanism by which Ser-175 phosphorylation affects transport is unclear. The ATPase, microtubule-binding affinity, and processivity are unchanged between a phosphomimetic S175D and a nonphosphorylatable S175A construct. However, we find that application of force differentiates between the two. Placement of negative charge at Ser-175, through phosphorylation or mutation, leads to a lower stall force and decreased velocity under a load of 1 piconewton or greater. Sedimentation velocity experiments also show that addition of a negative charge at Ser-175 favors the autoinhibited conformation of kinesin. These observations imply that when cargo is transported by both dynein and phosphorylated kinesin, a common occurrence in the cell, there may be a bias that favors motion toward the minus-end of microtubules. Such bias could be used to tune transport in healthy cells when properly regulated but contribute to a disease state when misregulated.