Developmental Biology

Visualizing the function of pancreatic β-cells in vivo has been a long-sought goal for β-cell researchers. Unlike imaging of β-cells in mammalian species with conventional positron emission tomography and single-photon emission computed tomography, which only provides limited spatial-temporal resolution, transparent zebrafish embryos are a unique model that allows high-resolution fluorescent imaging of β-cells in their native physiological microenvironment in vivo. Here, we detail a protocol for real-time visualization of individual β-cell function in vivo in a non-invasive manner, through combination of a novel transgenic zebrafish reporter line Tg (ins:Rcamp1.07) with both a commercial spinning-disc confocal microscope and an in-house developed super-resolution microscope (2P3A-DSLM). The protocol described here allows for the longitudinal monitoring of dynamic calcium activities from heterogeneous β-cells in early developing zebrafish embryos and is readily adaptable for use in imaging other important processes in islet biology, as well as screening new compounds that can promote β-cell function or maturation using a living whole organism system.

Extracellular ATP is a potent signaling molecule that stimulates intracellular calcium responses through purinergic (P2) receptors in mammalian cells. While extracellular ATP and intracellular calcium can be measured separately, simultaneous monitoring can offer additional insights into P2 receptor physiology. This protocol takes advantage of the overlapping fluorescence spectra between the ATP-detection substrate luciferin and calcium indicator dye Fura2. Mammalian cells are loaded with Fura2-AM and live-cell recordings are acquired in the presence of a luciferin-luciferase imaging solution. This protocol allows to study stimulus-induced ATP release and directly relate changes in extracellular ATP concentration to observed calcium responses.