Autonomous regulation of free Ca2+ concentrations in isolated plant cell nuclei: A mathematical analysis

Abstract

2+] nuc , nucleoplasmic free calcium concentration; [Ca 2+ ] nuc_total , nucleoplasmic total calcium concentration; [Ca 2+ ] store , nuclear store free calcium concentration; [Ca 2+ ] store_total , nuclear store total calcium concentration. AbstractExperiments performed on nuclei isolated from animal or plant cells have provided evidence that the nucleus generates directly specific nucleoplasmic calcium transients in response to external stimuli. Recent data suggest that isolated plant nuclei might be considered as a closed system where the nuclear concentration of free calcium would be regulated by reversible movements between the nucleoplasm and nuclear stores. We have addressed the relevance of this hypothesis by developing a mathematical approach to simulate nucleoplasmic calcium dynamics generated under various pH and temperature conditions. Here, we show that the experimental results could be explained provided that calciumchannels as well as systems transporting calcium are present on the inner nuclear membrane. The putative channels would allow the entry of calcium into the nucleoplasm whereas the elusive transporting system(s) would contribute to replenish the nuclear stores. The simple proposed model is versatile enough to explain and predict autonomous changes in free calcium in the nucleoplasm of isolated plant nuclei.1

Nuclear membranes control symbiotic calcium signaling of legumes

“…(Scale bars, 5 μm in A and B, 10 μm in C and D.) able to achieve calcium release outside the nucleus of up to 1.8 μM within 2 s. However, even under these conditions the calcium that diffuses through the pores into the nucleus only reaches an average concentration of 25 nM within this time, well below the concentrations measured during symbiotic calcium oscillations (3), although these measurements are only an approximation. These low calcium diffusion rates for the nuclear pores are explained by the very low permeability of the nuclear pore complement: if we take an exceptionally conservative value of 150 μm 2 (27) for the surface of the nucleus (whereas nuclei in M. truncatula seem to be more on the order of 600-800 μm 2 ), then 4,000 pores at their typical resting diameter account for only 0.1% of the nuclear surface, and 4,000 fully dilated pores would only occupy 1.3%. These figures and the full simulations suggest that diffusion through the pores is not likely to account for the near-simultaneous interior/exterior calcium changes.…”

Buffering Capacity Explains Signal Variation in Symbiotic Calcium Oscillations

“…Four of the model parameters have been taken from previous measurements: the volume of the nucleus (Brière et al, 2006), the capacitance of the nuclear envelope (Grygorczyk and Grygorczyk, 1998), the resting potential of Ca 2+ (Petersen et al, 1998), and a scaling factor relating total Ca 2+ changes to changes in free Ca 2+ (Brière et al, 2006). The remaining parameters have been estimated, and details on parameter estimation methods can be found in "Materials and Tables II and III and in Supplemental Table S1 for the supplemental figures.…”

Regulation of gene expression by NFAT transcription factors in hibernating ground squirrels is dependent on the cellular environment

“…, and 600 nM Ca 2+ added to the transcription factor binding buffer during the protein incubation step; 100 and 600 nM of Ca 2+ were selected because they represent the minimum and maximum concentrations of nuclear Ca 2+ that have been identified mathematically and experimentally (Brière et al 2006;Xiong et al 2012;Luan 2011;Dobi and Agoston 1998). A similar experiment was performed to assess for the effect of urea on transcription factor-DNA binding, with quantification runs being conducted for the LT samples (n = 4) with no protein and no urea (negative controls), no urea, 5 mM urea, and 100 mM urea added to the transcription factor binding buffer during the protein incubation step.…”