Showing 1 - 4 of 4 results
1.
STIM1 and Endoplasmic Reticulum-Plasma Membrane Contact Sites Oscillate Independently of Calcium-Induced Calcium Release.
Abstract:
Calcium (Ca2+) release from intracellular stores, Ca2+ entry across the plasma membrane, and their coordination via store-operated Ca2+ entry (SOCE) are critical for receptor-activated Ca2+ oscillations. However, the precise mechanism of Ca2+ oscillations and whether their control loop resides at the plasma membrane or intracellularly remain unresolved. By examining the dynamics of stromal interaction molecule 1 (STIM1), an endoplasmic reticulum (ER)-localized Ca2+ sensor that activates the Orai1 channel on the plasma membrane for SOCE and in mast cells, we found that a significant proportion of cells exhibited STIM1 oscillations with the same periodicity as Ca2+ oscillations. These cortical oscillations, occurring in the cell's cortical region and shared with ER-plasma membrane (ER-PM) contact site proteins, were only detectable using total internal reflection fluorescence microscopy (TIRFM). Notably, STIM1 oscillations could occur independently of Ca2+ oscillations. Simultaneous imaging of cytoplasmic Ca2+ and ER Ca2+ with SEPIA-ER revealed that receptor activation does not deplete ER Ca2+, whereas receptor activation without extracellular Ca2+ influx induces cyclic ER Ca2+ depletion. However, under such nonphysiological conditions, cyclic ER Ca2+ oscillations lead to sustained STIM1 recruitment, indicating that oscillatory Ca2+ release is neither necessary nor sufficient for STIM1 oscillations. Using optogenetic tools to manipulate ER-PM contact site dynamics, we found that persistent ER-PM contact sites reduced the amplitude of Ca2+ oscillations without alteration of oscillation frequency. Together, these findings suggest an active cortical mechanism governs the rapid dissociation of ER-PM contact sites, thereby controlling the amplitude of oscillatory Ca2+ dynamics during receptor-induced Ca2+ oscillations.
2.
Descending pathway facilitates undulatory wave propagation in Caenorhabditis elegans through gap junctions.
Abstract:
Descending signals from the brain play critical roles in controlling and modulating locomotion kinematics. In the Caenorhabditis elegans nervous system, descending AVB premotor interneurons exclusively form gap junctions with the B-type motor neurons that execute forward locomotion. We combined genetic analysis, optogenetic manipulation, calcium imaging, and computational modeling to elucidate the function of AVB-B gap junctions during forward locomotion. First, we found that some B-type motor neurons generate rhythmic activity, constituting distributed oscillators. Second, AVB premotor interneurons use their electric inputs to drive bifurcation of B-type motor neuron dynamics, triggering their transition from stationary to oscillatory activity. Third, proprioceptive couplings between neighboring B-type motor neurons entrain the frequency of body oscillators, forcing coherent bending wave propagation. Despite substantial anatomical differences between the motor circuits of C. elegans and higher model organisms, converging principles govern coordinated locomotion.
3.
Frequency and amplitude control of cortical oscillations by phosphoinositide waves.
Abstract:
Rhythmicity is prevalent in the cortical dynamics of diverse single and multicellular systems. Current models of cortical oscillations focus primarily on cytoskeleton-based feedbacks, but information on signals upstream of the actin cytoskeleton is limited. In addition, inhibitory mechanisms--especially local inhibitory mechanisms, which ensure proper spatial and kinetic controls of activation--are not well understood. Here, we identified two phosphoinositide phosphatases, synaptojanin 2 and SHIP1, that function in periodic traveling waves of rat basophilic leukemia (RBL) mast cells. The local, phase-shifted activation of lipid phosphatases generates sequential waves of phosphoinositides. By acutely perturbing phosphoinositide composition using optogenetic methods, we showed that pulses of PtdIns(4,5)P2 regulate the amplitude of cyclic membrane waves while PtdIns(3,4)P2 sets the frequency. Collectively, these data suggest that the spatiotemporal dynamics of lipid metabolism have a key role in governing cortical oscillations and reveal how phosphatidylinositol 3-kinases (PI3K) activity could be frequency-encoded by a phosphatase-dependent inhibitory reaction.
4.
Computational evidence for the role of Arabidopsis thaliana UVR8 as UV-B photoreceptor and identification of its chromophore amino acids.
Abstract:
A homology model of the Arabidopsis thaliana UV resistance locus 8 (UVR8) protein is presented herein, showing a seven-bladed β-propeller conformation similar to the globular structure of RCC1. The UVR8 amino acid sequence contains a very high amount of conserved tryptophans, and the homology model shows that seven of these tryptophans cluster at the 'top surface' of the UVR8 protein where they are intermixed with positive residues (mainly arginines) and a couple of tyrosines. Quantum chemical calculations of excitation spectra of both a large cluster model involving all twelve above-mentioned residues and smaller fragments thereof reveal that absorption maxima appearing in the 280-300 nm range for the full cluster result from interactions between the central tryptophans and surrounding arginines. This observation coincides with the published experimentally measured action spectrum for the UVR8-dependent UV-B stimulation of HY5 transcription in mature A. thaliana leaf tissue. In total these findings suggest that UVR8 has in fact in itself the ability to be an ultraviolet-B photoreceptor in plants.
