Open-space microfluidics as a tool to study signaling dynamics

The temporal dynamics of cell signaling are a crucial way for cells to regulate their transcriptional targets and consequently may heavily influence cell responses. Improving our understanding of signaling dynamics is important for drug treatments targeting specific signaling pathways. However, studying signaling dynamics requires multiplexed, time-sensitive experiments. Here, we use an open-space microfluidic device, the microfluidic display, which enables liquid delivery from above a surface, forming defined and stable confinement zones without enclosing samples into a chip. A device with rapid reagent switching (<7 seconds) and 6 independent confinement areas is first designed. Using this platform, we study the Notch pathway in engineered C2C12 cells to display constitutively active Notch receptors upon which we force highly controlled time-dependent modulation patterns by delivering time-varying doses of the Notch inhibitor DAPT. We replicate previous findings on Notch activation with our methodology by confirming the Notch-regulated gene Hes1 is upregulated for short Notch activation pulses, while Hey1 required sustained activation. We confirm a previously observed regime switch from Hes1 to Hey1 dominance between 2 h and 3 h of activation. Finally, by varying signal pulses while keeping dose constant in six independent experiments performed simultaneously, we further show the upregulation of the Hes1 gene for multiple short pulses, while Hey1 activation depends on duty cycle length. These results highlight microfluidic displays as a valuable tool for systems biology, enabling multiplexed, high temporal resolution stimulation of signaling pathways.