Single cell study of Notch-Delta cell signalling: entrainment and synchronisation of Hes1 mRNA and protein oscillations.

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Chiara Fracassi, Immacolata Garzilli, Luca Cardone, Diego di Bernardo

Fondazione Telethon - TIGEM, Italy

Cyclic expression of genes (i.e. oscillation) is involved in basic processes such as the cell cycle and the circadian clock. Ultradian oscillations, i.e. with periods much shorter than 24 hours, have been observed also in the major signalling pathways, but their relevance is still unclear. Little is known about how cells orchestrate their individual clocks in order to obtain a collective behaviour: this happens when a population of oscillators starts “beating in time”, or synchronise. Here we investigate the role of synchronisation of oscillations of the Notch-effector Hes1 using a model system mouse myoblasts (C2C12), where Hes1 oscillations are prominent. When investigating properties such as cyclic gene expression, the bias of dealing with a population of cells must be taken into account; experimental measurements reflect the average behaviour of the cell population, which can be very different from what happens in the single cell. To this aim, we took advantage of an innovative microfluidic platform (Kolnik et al., 2012) and of engineered Hes1 reporters, to study the properties of the Hes1 oscillator by applying periodic stimuli in time-lapse fluorescence microscopy over several days. Understanding pulses of different signalling molecules affect synchronisation of cell-autonomous oscillators will ultimately allow to gain insight on the role of oscillations in the coordination of a collective response at the population level. [This work was funded by the European Community’s Seventh Framework Programme [FP7/2007-2013] under grant agreement n° 259743 (MODHEP) and by the Telethon Foundation Grant TGM11SB1 to DdB]