A novel mode of cytokinesis without cell-substratum adhesion

Abstract

Cytokinesis is a final step in cell division. Dictyostelium cells, a model organism for the study of cytokinesis, have multiple modes, denoted cytokinesis A, B, C, and D. All these modes have been mainly investigated using cells adhering to the substratum although they can grow in shaking suspension culture. Here, we observed how cells divide without adhering to the substratum using a new non-adhesive material. These detached cells formed the cleavage furrow but eventually failed in the final abscission. Thus, the cells cannot divide without adhesion, suggesting that they cannot divide only through the conventional cytokinesis A. However, in a long-term culture, the detached cells adhered each other to form multicellular aggregates and divided properly in these aggregates. Myosin II-null cells also formed such aggregates but could not divide in the aggregates. Several lines of experiments using mutant cells showed that the process of cytokinesis in multicellular aggregates is a novel mode utilizing a confined space in the aggregate in a myosin II-dependent manner. These results shed light on a poorly characterized mechanism of cytokinesis in multicellular spheroids or tissues. We propose to redefine and classify multiple modes of cytokinesis.

γ -Ray Beams with Large Orbital Angular Momentum via Nonlinear Compton Scattering with Radiation Reaction

“…As a key result, a high energy γ-photon beam with both very high OAM and collimation is generated. In contrast to previous works [28][29][30][31][32][33] we further demonstrate that when radiation reaction is accounted for, part of the OAM and SAM of the absorbed laser photons is transferred to the electron beam. Moreover, the accompanying pair production process is shown to cause a counterintuitive increase of the OAM of the γ-beam due to extra absorption of twisted laser photons by secondary particles.…”

“…To bring these applications down to the nanometer and atomic scale [15], different methods are proposed to generate extreme-ultraviolet and x-ray vortex beams via high-order harmonic generation in a gas-phase atomic target [16][17][18], plasma [19][20][21], and helical undulator [22][23][24]. Recently, very promising concepts were developed to upgrade near-IR vortex beams to very high intensities [25][26][27], which provides the possibility to generate γ-ray vortex beams using Compton/Thomoson scattering of twisted light off ultra-relativistic electrons [28][29][30][31][32][33].Twisted γ-photons once realized could have straightforward applications to drive specific nuclear transitions [33], and to control and manipulate the rotation of nuclear matter [29]. In another prospect, γ-ray beams with ultrahigh OAM could impact the dynamics of rotating astrophysical objects, such as rotating black holes and luminous pulsars.…”

“…Twisted γ-photons once realized could have straightforward applications to drive specific nuclear transitions [33], and to control and manipulate the rotation of nuclear matter [29]. In another prospect, γ-ray beams with ultrahigh OAM could impact the dynamics of rotating astrophysical objects, such as rotating black holes and luminous pulsars.…”

“…The topological charge of the emitted twisted γ-photons can be increased using multiphoton phenomena in stronger laser fields. In the classical regime x-and γ-rays with OAM have been demonstrated by Thomoson scattering of laser pulses with either orbital or spin angular momentum (SAM) at a moderate nonlinearity with ξ ∼ 1 [32,33]. In stronger laser fields with ξ 1 [27,41] not only the number of scattered photons, but also the nonlinearity is dramatically increased, which may enhance significantly the OAM of the emitted photon beam.…”

Analysis of high-harmonic generation in terms of complex Floquet spectral analysis

“…The study of the coherence transfer through the nonlinear interaction of an atom and/or molecule with the intense laser light may help to understand the generation of the optical vortex recently experimentally observed. [9,10] As the interaction with the radiation field increases, the use of the perturbation method becomes inappropriate to describe the dynamics. Instead, Floquet method is a powerful tool to investigate the time evolution of a quantum state under a strong periodic external field.…”