Subgroup Saturday is arguably one of the best parts of BPS meetings. Attendees have the opportunities to hear interesting and exciting talks in their specific fields, interact with leaders in the field, and hopefully learn something new. This Subgroup Saturday has lived up to its reputation. Today, I attended the Biological Fluorescence Subgroup, which featured a diverse lineup of speakers.
First, Don Lamb from Ludwig Maximilian University of Munich, Germany started off the session by describing his groups collaborative work to understand how new HIV particles form and mature in host cells. His group has used a variety of fluorescence microscopy techniques to study recruitment of group-specific antigen (Gag) to the plasmid membrane and viral particle formation. Overall, Don showed there are two subpopulations of Gag based on diffusivity which is influenced by RNA interactions, Gag recruitment and assembly at the plasma membrane occurs in three phases, and nascent viral particle maturation and budding occurs in 2-3 minutes.
Second, Ralf Jungmann from the Max Plank Institute discussed his groups work on “localizomics” which he defined as omics approaches with localization. Using DNA-PAINT and Exchange-PAINT, his group is able to perform multiplexed imaging with one fluorophore. To improve molecular resolution and aid in acquiring DNA-PAINT images, his lab has developed liteTIRF, a compact and relatively inexpensive total internal reflection fluorescence microscopy (TIRF) microscope. Moving towards working in whole cells, the Jungmann lab has utilized SOMAmers, DNA aptamers with slow on and off rates, which was used to image multiple protein targets in one cell and identify nuclear versus cytoplasmic sides of nuclear pore complexes. Using kinetic barcoding, the lab has been able to perform 124-color super resolution imaging. Ralf presented work highlighting how DNA-PAINT and related technologies can be applied to image protein localizations at super resolution.
Third, Alessandra Cambi from Radboud Institute for Molecular Life Sciences presented work on understanding actin dynamics in podosomes of dendritic cells. Podosomes are cell protrusions responsible for topography sensing, antigen sampling, and matrix degradation. Podosomes are connected through dynamic actin networks, and the Cambi group has shown podosomes to contain a branched, beta-actin enriched core surrounded by bundled gamma-actin. Alessandra showed myosin is dynamically recruited to actin filaments and is enriched at dorsal actin fibers. The group found substrate stiffness influences podosomes; less vinculin-rich actin filaments are present in cells grown on soft substrates, and mesoscale-coordination is limited. Functionally, cells grown on stiff substrates are more capable of digesting gelatin than those on soft substrate, which were suggested to be able to push barriers to the side. Overall, Alessandra highlighted her key findings on podosome composition and the biological implications of podosome function.
Fourth, Bin Wu from Johns Hopkins University shared his group’s work on studying localized gene expression in the dendrites of neurons. Using single-molecule imaging of nascent peptides (SINAPS), his group is able to visualize protein translation by labeling newly synthesized protein and mRNA. With SINAPS, he found translation to occur spatially, where more translation occurred closer to the soma, and less translation occurred in distal regions of dendrites. His group also found translating mRNAs to be mobile in dendrites where bursts of translation occur, corresponding to the synthesis of 20-30 new proteins, demonstrating local gene expression occurs in dendrites. Altogether, Bin showed that protein synthesis can occur throughout the cell, allowing for spatiotemporal regulation of protein expression.
Fifth, Luke Lavis from Janelia Research Campus provided a brief history of the development of Janelia Fluor (JF) dyes and highlighted where his group are focusing their current efforts. In particular, Luke highlighted how the addition of azetidine moieties to tetramethyl rhodamine resulted in a new fluorophore with improved spectral properties, which we know as JF 549. Aside from making multicolored, photoactivatable, blinking, Halo tag compatible, and photosensitizing JF dyes, the Lavis group is working to apply JF dyes in functional imaging. Using chemigenetic approaches, the Lavis group combines the best of JF dyes with the best of genetically encoded biosensors. This approach has been used to make a new voltage indicator, Voltron, which is composed of opsin fused with a Halo tag. Addition of a Halo-compatible JF dye results in a fluorescent voltage indicator, which has enabled voltage imaging in vivo of mice neurons. Overall, Luke provided an excellent prospective on where JF dyes have come, and where he and others are applying fluorescent dyes now for functional imaging.
Finally, Elizabeth Hillman from Columbia University highlighted her groups work towards engineering a microscope capable of high-speed fluorescent 3D imaging of whole organisms. Her group has developed swept, confocally-aligned planar excitation microscopy (SCAPE), which Elizabeth described as a “weird super-fast version of light sheet microscopy that is kinda crossed with confocal microscopy, sort of.” The compact SCAPE design combines light sheet microscopy with a scanning galvo mirror, while all other microscope components to remain stationary. This design allows for fast imaging of live worms, fly larvae, beating zebrafish hearts, whole mouse brains, and other organisms without the need for image reconstruction. The Hillman lab is expanding upon the original SCAPE design to develop a 2-photon microscope, a microscope for imaging clarified tissues, and a clinically applicable microscope for in situ histology. Elizabeth gave an overview of the very exciting work her lab is doing to develop a fluorescence microscope capable of fast imaging of whole organisms.
After the scheduled talks, the session organizers invited several poster presenters to give a quick overview of their posters. I thought this was a great way to get attendees interested in the upcoming poster sessions and highlight interesting work that will be presented at the meeting throughout the next few days.
Subgroup Saturday Biological Fluorescence was awesome! I’m looking forward to the rest of #BPS19 and sharing exciting biophysics with you on the blog!
-Danielle