Verma Amitabh

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Verma
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Amitabh
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  • Article
    Quantification of collagen organization in histopathology samples using liquid crystal based polarization microscopy
    (The Optical Society, 2017-08-29) Keikhosravi, Adib ; Liu, Yuming ; Drifka, Cole ; Woo, Kaitlin M. ; Verma, Amitabh ; Oldenbourg, Rudolf ; Eliceiri, Kevin
    A number of histopathology studies have utilized the label free microscopy method of Second Harmonic Generation (SHG) to investigate collagen organization in disease onset and progression. Here we explored an alternative label free imaging approach, LC-PolScope that is based on liquid crystal based polarized light imaging. We demonstrated that this more accessible technology has the ability to visualize all fibers of interest and has a good to excellent correlation between SHG and LC-PolScope measurements in fibrillar collagen orientation and alignment. This study supports that LC-PolScope is a viable alternative to SHG for label free collagen organization measurements in thin histology sections.
  • Article
    Cytokinesis in vertebrate cells initiates by contraction of an equatorial actomyosin network composed of randomly oriented filaments
    (eLife, 2017-11-06) Spira, Felix ; Cuylen-Haering, Sara ; Mehta, Shalin B. ; Samwer, Matthias ; Reversat, Anne ; Verma, Amitabh ; Oldenbourg, Rudolf ; Sixt, Michael ; Gerlich, Daniel W.
    The actomyosin ring generates force to ingress the cytokinetic cleavage furrow in animal cells, yet its filament organization and the mechanism of contractility is not well understood. We quantified actin filament order in human cells using fluorescence polarization microscopy and found that cleavage furrow ingression initiates by contraction of an equatorial actin network with randomly oriented filaments. The network subsequently gradually reoriented actin filaments along the cell equator. This strictly depended on myosin II activity, suggesting local network reorganization by mechanical forces. Cortical laser microsurgery revealed that during cytokinesis progression, mechanical tension increased substantially along the direction of the cell equator, while the network contracted laterally along the pole-to-pole axis without a detectable increase in tension. Our data suggest that an asymmetric increase in cortical tension promotes filament reorientation along the cytokinetic cleavage furrow, which might have implications for diverse other biological processes involving actomyosin rings.
  • Preprint
    pH dependent isotropic to nematic phase transitions in graphene oxide dispersions reveal droplet liquid crystalline phases
    ( 2014-05) Tkacz, Rachel ; Oldenbourg, Rudolf ; Mehta, Shalin B. ; Miansari, Morteza ; Verma, Amitabh ; Majumder, Mainak
    Size fractionation, amplified by the surface charge density of graphene oxide (GO) sheets, broadens the pH dependent isotropic (I) to nematic (N) phase transition in aqueous dispersions of graphene oxide (GO). In this biphasic region, a highly organized droplet nematic phase of uniform size (20 ± 2.8 μm diameter) with an isotropic interior is observed.
  • Preprint
    Polarized light microscopy in reproductive and developmental biology
    ( 2013-05) Koike-Tani, Maki ; Tani, Tomomi ; Mehta, Shalin B. ; Verma, Amitabh ; Oldenbourg, Rudolf
    The polarized light microscope reveals orientational order in native molecular structures inside living cells, tissues, and whole organisms. Therefore, it is a powerful tool to monitor and analyze the early developmental stages of organisms that lend themselves to microscopic observations. In this article we briefly discuss the components specific to a traditional polarizing microscope and some historically important observations on chromosome packing in sperm head, first zygote division of the sea urchin, and differentiation initiated by the first uneven cell division in the sand dollar. We then introduce the LC-PolScope and describe its use for measuring birefringence and polarized fluorescence in living cells and tissues. Applications range from the enucleation of mouse oocytes to analyzing the polarized fluorescence of the water strider acrosome. We end by reporting first results on the birefringence of the developing chick brain, which we analyzed between developmental stages of days 12 through 20.