Even when nothing appears to be happening on the surface, signaling events are constantly occurring within cells. Living cells continuously sense the surrounding environment and commit to the tissue maintenance.

In our lab, we observe the activity of ERK, a multifunctional signaling molecule, at the level of individual cells. Through live imaging, we uncover stochastic fluctuations and wave-like propagation of signaling activity, revealing autonomous modes of regulation that govern cells and tissues (Hiratsuka et al., Elife 2015).

Directly observing what happens to individual cells during homeostasis and diseases is one of the major advantages of live imaging. The observation of single cells is especially important In cancer research as individual cancer cells exhibit remarkable variability, a phenomenon known as tumor heterogeneity.

To capture these diverse cancer cell behaviors, we extend our imaging approaches to living tumor tissues (intravital imaging).

In the image on the left, each round object represents the nucleus of a pancreatic tumor cell, while the magenta signal indicates the surrounding collagen fibers. This approach allows us to follow tumor development and drug responses over long periods in the mouse pancreas tissue.

Understanding the complex signal dynamics requires quantitative data analysis. Signal activities occasionally fluctuate in pulse-like patterns and can even propagate to neighboring cells. These spatiotemporal features can be characterized through spatial mapping and single-cell time-course analyses.

With recent advances in AI and machine learning, image analysis now offers expanding possibilities to statistically evaluate and even predict biological phenomena.

The map on the left shows drug responses of a population of tumor cells in the living pancreas. While most cells died (purple dots), a cluster of cells survived (red circle) and retained high ERK activity.

Would you describe yourself as a indecisive person? Actually that is something happening in your cells as well. ERK signal activity is highly pulsatile in epidermal stem cells and its down-regulation coincides with the initiation of the differentiation program. 

The single-cell signal flutuation is not detectable without live imaging technologies - sensitive fluorescent probes, microscopy, and image analyses. Live imaging always offers excitements with unexpecte appearances.