Calcium, BOBs, QEDs, microdomains and a cellular decision: Control of mitotic coli division in sand dollar blastomeres

The role of Ca²⁺ in controlling cell processes (e.g. mitosis) presents an enigma in its ubiquity and selectivity. Intracellular free Ca²⁺ (Ca²⁺(i)) is an essential regulator of specific biochemical and physiological aspects of mitosis (e.g. nuclear envelope breakdown (NEB)). Changes in Ca²⁺(i) concentrations during mitosis in second cell-cycle sand dollar (Echinaracnius parma) blastomeres were imaged as Ca²⁺-dependent luminescence of the photoprotein aequorin with multi-spectral analytical video microscopy. Photons of this luminescence were seen as bright observable blobs (BOBs). Spatiotemporal patterns of BOBs were followed through one or more cell cycles to detect directly changes in Ca²⁺(i), and were seen to change in a characteristic fashion prior to NEB, the onset of anaphase chromosome movement, and during cytokinesis. These patterns were observed from one cell cycle to the next in a single cell, from cell to cell, and from egg batch to egg batch. In both mitosis and synaptic transmission increases in Ca²⁺, concentration occurs in discrete, short-lived, and highly localized pulses we named quantum emission domains (QEDs) within regions we named microdomains. Signal and statistical optical analyses of spatiotemporal BOB patterns show that many BOBs are linked by constant displacements in space-time (velocity). Linked BOBs are thus nonrandom and are classified as QEDS. Analyses of QED patterns demonstrated that the calcium signals required for NEB are nonrandom, and are evoked by an agent(s) generated proximal to a Ca²⁺(i)-QED; models of waves, diffusible agonists and Ca²⁺-activated Ca²⁺ release do not fit pre-NEB cell data. Spatial and temporal resolution of this multispectral approach significantly exceeds that reported for other methods, and avoids the perturbations associated with many fluorescent Ca²⁺ reporters that interfere with cells being studied (Ca²⁺-buffering, UV toxicity, etc.). Spatiotemporal patterns of Ca²⁺(i)-QED can control so many different processes, i.e. specific frequencies used to control particular processes. Predictive and structured patterns of calcium signals (e.g. a language expressed in Ca²⁺) may selectively regulate specific Ca²⁺-dependent cellular processes.