Revolutionary tool reveals hidden brain cell functions

Resume: Researchers developed ConVERGD, a tool for precise manipulation of specific cell subpopulations, improving research into cellular diversity. The study demonstrated the utility of ConVERGD by identifying a subpopulation of norepinephrine neurons associated with anxiety. This innovative approach could impact research and treatment in several areas.

Key Facts:

  • Precision tools: ConVERGD enables precise targeting and manipulation of cell subpopulations.
  • Neuroscientific application: Used to identify a subpopulation of norepinephrine neurons that influences anxiety.
  • Broad impact: Potential applications beyond neuroscience, benefiting several areas of research.

Source: St. Jude Children’s Research Hospital

As gene sequencing technologies become more powerful, our understanding of cellular diversity has grown in parallel. This led scientists at St. Jude Children’s Research Hospital to create a tool to improve the ease and accuracy with which researchers can study specific subpopulations of cells.

The tool, called Conditional Viral Expression of Ribozyme Guided Degradation (ConVERGD), allows researchers to specifically access these subsets of cells and precisely manipulate them based on multiple characteristics of the cell.

Importantly, ribozymes can be designed to control the on/off switch for gene expression with pinpoint precision. Credit: Neuroscience News

ConVERGD offers numerous advantages over existing intersectional expression platforms by accommodating more complex genetic payloads and greater adaptability.

The researchers demonstrated the utility of ConVERGD by studying a previously unidentified subpopulation of norepinephrine neurons. The work demonstrates the substantial impact that research into cellular subpopulations could have on basic research and healthcare.

The findings were published today in Nature Neuroscience.

Same type of cells, different functions

For Lindsay Schwarz, PhD, St. Jude Department of Developmental Neurobiology, necessity was the driving force behind invention as she explored the neuronal cell landscape, and in particular, neuronal cells that produce norepinephrine.

“It is thought that norepinephrine neurons are just one type of neuron. But when activated in the brain, they can cause many different behaviors, such as improving attention and memory formation or triggering a stress response or fight-or-flight response,” Schwarz said.

“But if it’s just one type of neuron that releases this one molecule, how does it make you do other things?”

Investigating such questions requires the ability to selectively interrogate cellular subpopulations with extreme bias. To this end, Schwarz found that all attempts using current practices fell short.

“We didn’t go into this project thinking we were going to build a new tool, but it seemed like a need in the community.”

Improving current targeting technology for mobile subpopulations

To target subpopulations of cells, they must be passed through different genetic filters. These intersectional filters examine which genes the cells express and what pathways and connections they make, parsing out the different subpopulations so researchers can focus on a select group of isolated cells.

The use of adeno-associated virus (AAV)-based reporter tools that can deliver genetic material into specific cells with high precision is an ideal approach for applying these intersectional filters.

These reporter tools are used to label or monitor gene expression and protein localization within specific cells or regions. However, they can be complex to design and provide a limited amount of space.

“One of our main goals was to design a tool that would only express the gene you’re interested in if it was transferred with multiple functions, but would allow end users to very easily edit and put in whatever genes they want,” Schwarz explains.

Robust ribozymes provide next-generation specificity

Schwarz and first author Alex Hughes, PhD, a graduate of the St. Jude Graduate School of Biomedical Sciences, currently at the Allen Institute for Brain Science, designed ConVERGD using two separate technologies, AAV-based reporter technology and inspiration from the world of ribozymes, RNA strands that can behave like enzymes by catalyzing biochemical reactions.

Importantly, ribozymes can be designed to control the on/off switch for gene expression with extreme precision.

“We initially heard about ribozymes from a journal club that was thinking more therapeutically about using AAVs,” Schwarz said. “Alex came back and thought he could figure out a way to use this in neuroscience tools.”

Exciting for the neuroscience community and beyond

As a proof-of-concept, Schwarz and Hughes used ConVERGD to interrogate a subpopulation of norepinephrine neurons.

“Collectively, norepinephrine neurons do many different things,” Schwarz explained.

“The subset we focused on makes norepinephrine, but they also make another opioid peptide called dynorphin, which has not been previously characterized in these neurons. With ConVERGD, we found that activating just these dynorphin-expressing neurons was sufficient to induce a fear response.”

By dissecting the functions and assigning them to a subpopulation of cells, Schwarz hopes that targeted therapy is a possibility.

“We treat anxiety and depression with drugs that target norepinephrine signaling, but they target it globally,” Schwarz said.

“You will also see a downside to other important functions of norepinephrine that you don’t want to see. Targeting these neurons more specifically could help improve this.”

The work will have ripple effects beyond St. Jude. “We’re really excited about this for the community,” Schwarz said. “ConVERGD must be able to be used by any tissue. It could be useful beyond neuroscience.”

Authors and funding

The study’s other authors are Brittany Pittman, Beisi Xu, Jesse Gammons, Charis Webb, Hunter Nolen, Phillip Chapman and Jay Bikoff, St. Jude.

The study was supported by grants from the Brain & Behavior Research Foundation (NARSAD Young Investigator Grant), the National Institutes of Health (1DP2NS115764, P30 CA021765), and ALSAC, St. Jude’s fundraising and awareness organization.

About this neurotech research news

Author: Chelsea Bryant
Source: St. Jude Children’s Research Hospital
Contact: Chelsea Bryant – St. Jude Children’s Research Hospital
Image: The image is credited to Neuroscience News

Original research: Closed access.
“An intersectional single-vector AAV strategy for interrogating cellular diversity and brain function” by Lindsay Schwarz et al. Nature Neuroscience


An intersectional single-vector AAV strategy for interrogating cellular diversity and brain function

As the discovery of cellular diversity in the brain accelerates, so does the need for tools that target cells based on multiple characteristics.

Here we developed Conditional Viral Expression by Ribozyme Guided Degradation (ConVERGD), an adeno-associated virus-based, single-construct, intersectional targeting strategy that combines a self-cleaving ribozyme with traditional FLEx switches to deliver molecular cargo to specific neuronal subtypes.

ConVERGD offers advantages over existing intersectional expression platforms, such as comprehensive intersectional targeting with up to five recombinase-based features, accommodation of larger and more complex payloads, and a vector that is easily customizable for rapid expansion of the toolkit.

In the current report, we used ConVERGD to characterize an unexplored subpopulation of norepinephrine (NE)-producing neurons within the locus coeruleus of rodents that co-express the endogenous opioid gene prodynorphin (Pdyn).

These studies demonstrate ConVERGD as a versatile tool for targeting and revealing diverse cell types PdynExpress -NE+ locus coeruleus neurons as a small neuronal subpopulation capable of mediating anxiogenic behavioral responses in rodents.

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