New Fast Genetically Encoded Calcium Indicators: jGCaMP8

The principle of calcium ion imaging technology lies in the properties of calcium ion-sensitive proteins (genetically encoded calcium indicators, GECIs). Taking the GCaMP protein as an example, the binding of calcium and the GCaMP protein can stimulate the emission of green fluorescence, so that the experimenter can collect and record the instantaneous fluorescence changes by means of two-photon fluorescence microscope or optical fiber recording.

Figure 1 The basic structure and principle of GCaMP protein (Sun, 2013)

Neuroscience is the most widely used subject of calcium imaging technology. Based on GECIs expressed by genetic methods, scientists can observe the cell activities of the nervous system non-invasively. The application of calcium ion imaging

technology in neuroscience includes: observing and recording the activities of population cells (mainly tracking the fluorescent signals of cell bodies), and recording the activities of cell substructural units (such as axons, dendrites, or local synapses). With the increasing demand for research, people continue to improve calcium-sensitive proteins. At present, the more mature ones are the GCaMP6 and jGCaMP7 series. With the help of these tools, we can detect changes in calcium ions caused by a single action potential, and the observation time can be accurate to the millisecond level, up to several months of continuous observation.

GCaMP6 Series

The sixth-generation GCaMP protein (GCaMP6) includes three different subtypes: GCaMP6s, GCaMP6m, and GCaMP6f, which have different characteristics and need to be selected according to experimental requirements [1].

jGCaMP7 Series

jGCaMP7 (Janelia GCaMP7, different from G-CaMP7), including four types of proteins with different characteristics: jGCaMP7s, jGCaMP7f, jGCaMP7b, jGCaMP7c[2]. The jGCaMP7 sensors were tested in vitro and in vivo, and show substantially better performance than the GCaMP6 sensors.

jGCaMP8 Series

Although GCaMP6 and jGCaMP7 have been widely verified and applied, there are still many shortcomings that need to be improved. Recently, we have been fortunate to see great progress in this field.

The Loren L. Looger laboratory of HHMI Janelia and the GENIE Project team have developed a new generation of GCaMP protein - jGCaMP8. The new jGCaMP8 sensor has a faster dynamic curve and a high degree of sensitivity [3]. Specifically, the sensors are:

• jGCaMP8f (fast): 4x faster rise time, 2.5x faster decay time than jGCaMP7f.
• jGCaMP8m (medium): almost 4x faster rise time and 3.5x more sensitive than jGCaMP7f.
• jGCaMP8s (sensitive): 2x more sensitive than jGCaMP7s, >2x faster than jGCaMP7f (at 1AP).

Figure 2 Reaction characteristics of jGCaMP8 protein [3]

Appendix

Calcium Imaging Virus Vector List at Creative Biolabs

References

1. Tsai-Wen Chen. et al., Ultra-sensitive fluorescent proteins for imaging neuronal activity. Nature. 2013 Jul 18;499(7458):295-300. doi: 10.1038/nature12354.
2. Hod Dana, et al., High-performance GFP-based calcium indicators for imaging activity in neuronal populations and microcompartments bioRXiv, 2018, DOI: 10.1101/434589
3. Zhang et al Janelia Research Campus. Online resource. 2020
4. Sverre Grødem., et al. An updated suite of viral vectors for in vivo calcium imaging using local and retro-orbital injections. doi: https://doi.org/10.1101/2021.05.14.443815
5. Sun, Xiaonan R., et al. "Fast GCaMPs for improved tracking of neuronal activity." Nature communications 4.1 (2013): 1-10.