Calcium signaling and network activity : mathematical modeling and molecular mechanisms

Sammanfattning: The calcium (Ca2+) ion is a versatile second messenger present in all cells. It is involved in such diverse processes as cell division, differentiation, vesicle transport and muscle contraction. Its widespread applicability is partially explained by its wide temporal and spatial dynamics. By varying in time, oscillations arise and enable frequency modulation. Likewise, by varying in space, waves are formed and enable cross talk in-between cells in networks. In here, I present novel data on the mechanism behind Ca2+ signaling both in the form of oscillations and in the form of intercellular networks. The investigation are performed both from a theoretical point of view using mathematical modeling simulated in silico and from a molecular point of view in wet-lab experiments in vitro and in vivo. To be more specific, in Paper I, I present a method with software to identify functional networks in groups of cells and ways of analyzing them. In Paper II, this method is used to identify so-called small-world networks with scale-free properties in spontaneously active neural progenitor cells. These network formations are dependent on gap junctions and critically regulate proliferation both in neural progenitors derived from embryonic stem cells and in embryonic mouse brains. In Paper III, I present a model for the generation of spontaneous Ca2+ oscillations in neural progenitors. The essence of this model is that the spontaneous Ca2+ and electrical activity is driven by functional pacemaker cells expressing slightly more voltage-gated Ca2+ channels than the cells connected to them with gap junctions. Interestingly, one type of channel involved in this pacemaker activity is encoded by the mental disorder susceptibility gene Cacna1c. Transgenic mice lacking Cacna1c expression in the forebrain exhibit signs of increased anxiety as well as changes in brain anatomy. Finally in Paper IV, I describe a method of finding genes dependent on the frequency of Ca2+ oscillations. Cells stably expressing the light-sensitive protein melanopsin are exposed to light, after which the cellular content is collected and analyzed with RT-qPCR, RNA sequencing and phosphoproteomics. Hereby, a large network of genes and proteins dependent on frequency is identified. In conclusion, the research described below deepens our understanding on Ca2+ oscillations and network activity, using both mathematical modeling and wet-lab molecular biology experiments.