In vivo vascular flow profiling combined with optical tweezers based blood routing

2017 ◽  
Author(s):  
Robert Meissner ◽  
Wade W. Sugden ◽  
Arndt F. Siekmann ◽  
Cornelia Denz
Keyword(s):  
Optical Tweezers ◽  
Vascular Flow

scholarly journals Force generation by protein–DNA co-condensation

2021 ◽  
Author(s):  
Thomas Quail ◽  
Stefan Golfier ◽  
Maria Elsner ◽  
Keisuke Ishihara ◽  
Vasanthanarayan Murugesan ◽  
...  
Keyword(s):  
Optical Tweezers ◽  
Self Assembly ◽  
Spider Silk ◽  
Regulatory Elements ◽  
Heterochromatin Formation ◽  
First Order Phase Transition ◽  
Dna Strand ◽  
First Order Phase

AbstractInteractions between liquids and surfaces generate forces1,2 that are crucial for many processes in biology, physics and engineering, including the motion of insects on the surface of water3, modulation of the material properties of spider silk4 and self-assembly of microstructures5. Recent studies have shown that cells assemble biomolecular condensates via phase separation6. In the nucleus, these condensates are thought to drive transcription7, heterochromatin formation8, nucleolus assembly9 and DNA repair10. Here we show that the interaction between liquid-like condensates and DNA generates forces that might play a role in bringing distant regulatory elements of DNA together, a key step in transcriptional regulation. We combine quantitative microscopy, in vitro reconstitution, optical tweezers and theory to show that the transcription factor FoxA1 mediates the condensation of a protein–DNA phase via a mesoscopic first-order phase transition. After nucleation, co-condensation forces drive growth of this phase by pulling non-condensed DNA. Altering the tension on the DNA strand enlarges or dissolves the condensates, revealing their mechanosensitive nature. These findings show that DNA condensation mediated by transcription factors could bring distant regions of DNA into close proximity, suggesting that this physical mechanism is a possible general regulatory principle for chromatin organization that may be relevant in vivo.

scholarly journals Hemodynamic forces can be accurately measured in vivo with optical tweezers

2017 ◽  
Author(s):  
Sébastien Harlepp ◽  
Fabrice Thalmann ◽  
Gautier Follain ◽  
Jacky G. Goetz
Keyword(s):  
Optical Tweezers ◽  
Cell Biology ◽  
Accurate Determination ◽  
Force Measurements ◽  
Hemodynamic Forces ◽  
Non Invasive ◽  
Drag Forces ◽  
Measured Flow ◽  
Living Organisms

AbstractForce sensing and generation at the tissular and cellular scale is central to many biological events. There is a growing interest in modern cell biology for methods enabling force measurements in vivo. Optical trapping allows non-invasive probing of pico-Newton forces and thus emerged as a promising mean for assessing biomechanics in vivo. Nevertheless, the main obstacles rely in the accurate determination of the trap stiffness in heterogeneous living organisms, at any position where the trap is used. A proper calibration of the trap stiffness is thus required for performing accurate and reliable force measurements in vivo. Here, we introduce a method that overcomes these difficulties by accurately measuring hemodynamic profiles in order to calibrate the trap stiffness. Doing so, and using numerical methods to assess the accuracy of the experimental data, we measured flow profiles and drag forces imposed to trapped red blood cells of living zebrafish embryos. Using treatments enabling blood flow tuning, we demonstrated that such method is powerful in measuring hemodynamic forces in vivo with accuracy and confidence. Altogether, this study demonstrates the power of optical tweezing in measuring low range hemodynamic forces in vivo and offers an unprecedented tool in both cell and developmental biology.

scholarly journals Bio-Molecular Applications of Recent Developments in Optical Tweezers

Biomolecules ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 23 ◽  
Author(s):  
Dhawal Choudhary ◽  
Alessandro Mossa ◽  
Milind Jadhav ◽  
Ciro Cecconi
Keyword(s):  
Photonic Crystal ◽  
Optical Tweezers ◽  
Single Molecule ◽  
Continuous Wave ◽  
Imaging Techniques ◽  
Resolving Power ◽  
Optical Traps ◽  
Laser Source ◽  
One Dimensional

In the past three decades, the ability to optically manipulate biomolecules has spurred a new era of medical and biophysical research. Optical tweezers (OT) have enabled experimenters to trap, sort, and probe cells, as well as discern the structural dynamics of proteins and nucleic acids at single molecule level. The steady improvement in OT’s resolving power has progressively pushed the envelope of their applications; there are, however, some inherent limitations that are prompting researchers to look for alternatives to the conventional techniques. To begin with, OT are restricted by their one-dimensional approach, which makes it difficult to conjure an exhaustive three-dimensional picture of biological systems. The high-intensity trapping laser can damage biological samples, a fact that restricts the feasibility of in vivo applications. Finally, direct manipulation of biological matter at nanometer scale remains a significant challenge for conventional OT. A significant amount of literature has been dedicated in the last 10 years to address the aforementioned shortcomings. Innovations in laser technology and advances in various other spheres of applied physics have been capitalized upon to evolve the next generation OT systems. In this review, we elucidate a few of these developments, with particular focus on their biological applications. The manipulation of nanoscopic objects has been achieved by means of plasmonic optical tweezers (POT), which utilize localized surface plasmons to generate optical traps with enhanced trapping potential, and photonic crystal optical tweezers (PhC OT), which attain the same goal by employing different photonic crystal geometries. Femtosecond optical tweezers (fs OT), constructed by replacing the continuous wave (cw) laser source with a femtosecond laser, promise to greatly reduce the damage to living samples. Finally, one way to transcend the one-dimensional nature of the data gained by OT is to couple them to the other large family of single molecule tools, i.e., fluorescence-based imaging techniques. We discuss the distinct advantages of the aforementioned techniques as well as the alternative experimental perspective they provide in comparison to conventional OT.

Measuring stall forces in vivo with optical tweezers through light momentum changes

2011 ◽  
Author(s):  
J. Mas ◽  
A. Farré ◽  
C. López-Quesada ◽  
X. Fernández ◽  
E. Martín-Badosa ◽  
...  
Keyword(s):  
Optical Tweezers

scholarly journals Mechanically switching single-molecule fluorescence of GFP by unfolding and refolding

2017 ◽  
Vol 114 (42) ◽  
pp. 11052-11056 ◽  
Author(s):  
Ziad Ganim ◽  
Matthias Rief
Keyword(s):  
Optical Tweezers ◽  
Single Molecule ◽  
Optical Sensors ◽  
Structural Integrity ◽  
Fluorescent Protein ◽  
Single Molecule Fluorescence ◽  
Extended States ◽  
Green Fluorescent ◽  
Ensemble Experiments

Green fluorescent protein (GFP) variants are widely used as genetically encoded fluorescent fusion tags, and there is an increasing interest in engineering their structure to develop in vivo optical sensors, such as for optogenetics and force transduction. Ensemble experiments have shown that the fluorescence of GFP is quenched upon denaturation. Here we study the dependence of fluorescence on protein structure by driving single molecules of GFP into different conformational states with optical tweezers and simultaneously probing the chromophore with fluorescence. Our results show that fluorescence is lost during the earliest events in unfolding, 3.5 ms before secondary structure is disrupted. No fluorescence is observed from the unfolding intermediates or the ensemble of compact and extended states populated during refolding. We further demonstrate that GFP can be mechanically switched between emissive and dark states. These data definitively establish that complete structural integrity is necessary to observe single-molecule fluorescence of GFP.

scholarly journals Calibration of Optical Tweezers for In Vivo Force Measurements: How do Different Approaches Compare?

2014 ◽  
Vol 107 (6) ◽  
pp. 1474-1484 ◽  
Author(s):  
Yonggun Jun ◽  
Suvranta K. Tripathy ◽  
Babu R.J. Narayanareddy ◽  
Michelle K. Mattson-Hoss ◽  
Steven P. Gross
Keyword(s):  
Optical Tweezers ◽  
Force Measurements

scholarly journals Micromanipulation of amyloplasts with optical tweezers in Arabidopsis stems

2020 ◽  
Author(s):  
Yoshinori Abe ◽  
Keisuke Meguriya ◽  
Takahisa Matsuzaki ◽  
Teruki Sugiyama ◽  
Hiroshi Y. Yoshikawa ◽  
...  
Keyword(s):  
Optical Tweezers ◽  
Near Infrared ◽  
Initial Step ◽  
Optical Force ◽  
Physical Interaction ◽  
Laser Focus ◽  
Close Proximity ◽  
Endodermal Cells ◽  
Vacuolar Membranes

AbstractIntracellular sedimentation of highly dense, starch-filled amyloplasts toward the gravity vector is likely a key initial step for gravity sensing in plants. However, recent live-cell imaging technology revealed that most amyloplasts continuously exhibit dynamic, saltatory movements in the endodermal cells of Arabidopsis stems. These complicated movements led to questions about what type of amyloplast movement triggers gravity sensing. Here we show that a confocal microscope equipped with optical tweezers can be a powerful tool to trap and manipulate amyloplasts noninvasively, while simultaneously observing cellular responses such as vacuolar dynamics in living cells. A near-infrared (λ = 1064 nm) laser that was focused into the endodermal cells at 1 mW of laser power attracted and captured amyloplasts at the laser focus. The optical force exerted on the amyloplasts was theoretically estimated to be up to 1 pN. Interestingly, endosomes and trans-Golgi networks were trapped at 30 mW but not at 1 mW, which is probably due to lower refractive indices of these organelles than that of the amyloplasts. Because amyloplasts are in close proximity to vacuolar membranes in endodermal cells, their physical interaction could be visualized in real time. The vacuolar membranes drastically stretched and deformed in response to the manipulated movements of amyloplasts by optical tweezers. Our new method provides deep insights into the biophysical properties of plant organelles in vivo and opens a new avenue for studying gravity-sensing mechanisms in plants.

scholarly journals Condensin compacts DNA in 15 nm steps and requires FACT for extrusion on chromatin

2021 ◽  
Author(s):  
David Rueda ◽  
Swathi Sudhakar ◽  
Gemma Fisher ◽  
Pilar Gutierrez-Escribano ◽  
Jonay Garcia-Luis ◽  
...  
Keyword(s):  
Optical Tweezers ◽  
Fluorescence Detection ◽  
Histone Chaperone ◽  
Loop Formation ◽  
Step Size ◽  
Base Pairs ◽  
Extrusion Mechanism ◽  
Increasing Load ◽  
Nucleosome Arrays

Abstract Condensin plays a central role in the organisation of chromosomes by compacting chromatin into loops during mitosis. Condensin achieves this through a loop extrusion mechanism that remains poorly understood. To identify the molecular steps of yeast condensin during loop formation, we used optical tweezers with fluorescence detection. We find that single yeast condensin complexes use ATP to extrude DNA through distinct 15 nm steps, thus advancing ~45 base pairs (bp) per step. Under increasing load, the condensin step size remains constant while step-dwell times increase, and stalls at forces >1 pN. We also show that nucleosome arrays hinder processive condensin extrusion and demonstrate that the histone chaperone FACT is required for compaction of nucleosomal arrays by condensin. Importantly, FACT-assisted compaction on nucleosomes also occurs through distinct 15 nm steps. Finally, we show that FACT is required for correct condensin localisation in vivo. Our results establish that loop extrusion by yeast condensin involves a 45 bp stroke that requires FACT for condensin function on chromatin.

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