Akash Singh, Banaras Hindu University
Researchers at Ruhr-Universität Bochum have characterized a new reverse optogenetic tool using zebrafish, a protein that can be controlled by light. A zebrafish opsin—a protein that occurs in the brain and eyes—was introduced into the brain of a mouse to study how it affects the brain. An optogenetic tool can be turned on or off by light. In addition, the tool could be used to investigate brain changes that are responsible for epilepsy. Behavioral Neurobiology Research Group Professor Melanie Mark and Department of General Zoology & Neurobiology Professor Stefan Herlitze describe their experiments and results in the journal Nature Communications, published online on July 23, 2021.
Optogenetics and GPCRs:
Neuronal dynamics can be studied in a precise spatial and temporal manner using optogenetics. These proteins have greatly contributed to the current understanding of neuronal networks and surrounding signaling pathways. In most cases, GPCRs are activated by physical stimuli or by the binding of a chemical ligand. Some GPCRs have an intrinsic constitutive activity that is independent of agonists.
Certain forms of epilepsy are associated with changes in the function of GPCRs coupling to the Gi/o pathways that weaken neuronal activity via activation of G protein-coupled rectifying potassium (GIRK) channels. Opn7b is a G protein-coupled receptor found in zebrafish. It is shown to be constitutively active because it can be activated without a light stimulus. As a rule, the activation of G protein-coupled receptors leads to the opening of certain ion channels and, therefore, to ion influx into the cell. For Opn7b, light deactivates the signaling chain, which is permanently active in the absence of light.
It is believed that G protein-coupled receptors play a role in various psychiatric conditions. However, little research has been conducted on this topic in the last decades. Virally induced cancers also appear to be affected by these proteins.
Blue light stimulation of Opn7b:
Opn7b is constitutively active and Gi/o specific. To investigate whether they could modulate cortical circuit dynamics via Opn7b, they specifically expressed Opn7b in Plasma cells (PCs) using Nex-cre mice. This was followed by the application of pulses to determine if the increase in firing rate is related to a change in the resting membrane potential (Vm) and firing threshold of the PCs. The researchers in their draft reported that blue light stimulation of Opn7b increases neuronal activity in vitro. Also when stimulated by blue light leads to an increase in single-neuron and network activity in vivo.
An increase in network activity led them to investigate whether stimulation of Opn7b can be a useful tool to induce pathological network synchrony. They found that Light mediated Opn7b-mediated deactivation in the primary somatosensory cortex, induced epileptic form activity in mice.
Prospects:
Even though Opn7b is not likely to be useful for studying the native state of the cell, it can be used to study the mechanisms underlying constitutively active GPCR pathways in diseased states and psychiatric disorders. To test whether cell type and brain region-specific constitutive activation of Gi/o pathways modulate aging and neurodegeneration, Opn7b may also be used. A research tool to investigate constitutively active GPCR signaling pathways in altered and disease states, Opn7b can be used in a temporal and cell type-specific controlled manner.
Researchers believe that Opn7b is well-suited for gaining new insights into the function of constitutively active G protein-coupled receptors, as well as for gaining new knowledge about the receptors’ role in the development of diseases, where the receptors can be examined and regulated.
Also read: The first-ever CRISPR/Cas9 genome editing in marsupials
Reference:
- Karapinar, R., Schwitalla, J.C., Eickelbeck, D. et al. Reverse optogenetics of G protein signalling by zebrafish non-visual opsin Opn7b for synchronization of neuronal networks. Nat Commun 12, 4488 (2021). https://doi.org/10.1038/s41467-021-24718-0
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Author info:
Akash Singh is a first-year master’s student of Biochemistry at Banaras Hindu University. He plans to pursue Ph.D. in the future. He aims to research and teach the young minds of the country.
Social media links: LinkedIn: https://www.linkedin.com/in/akash-singh-82b5811a2/
Publications :
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