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Two sets of regulatory genes work hierarchically to group over 8,000 distinct neuron types into fewer than 200 modular structural ground plans. Credit: Neuroscience News<\/p>\nSummary: A new study established a simplified framework to analyze complex neural circuits by categorizing individual neurons into broad structural groupings. The research team focused on instinctual, hardwired decision-making behaviors in fruit flies (Drosophila).<\/p>\n
By mapping the developmental rules of the brain, investigators discovered that two distinct sets of regulatory genes work hierarchically to organize over 8,000 unique neuron types into fewer than 200 foundational structural \u201cground plans,\u201d providing a scalable blueprint to decipher mammalian neural architecture.<\/p>\n
Key Facts<\/p>\n
Circumventing Neuronal Complexity: Instead of evaluating all 8,000 individual neuron types in the fruit fly cerebrum manually, the new framework allows scientists to study how circuits function using fewer than 200 modular ground plans wired together for different tasks.The Dual-Gene Hierarchy: The discovery unmasks a strict genetic hierarchy that sets up these core ground plans:The First Gene Set: Coordinates and establishes the gross, macro-structural ground plans of the neurons.The Second Gene Set: Governs the fine-scale modifications, dictating precise shape differences and localized circuit connectivity.The \u201cTaste and Cease\u201d Axis: To validate this framework, researchers isolated a single ground plan dedicated to sensing a stimulus and stopping a behavior. Within this single macro-structure, they identified two distinct neural lines governed by the second gene set: one that detects unpalatable tastes to halt feeding, and another that registers undesirable pheromones to block mating.Mammalian Homologue Potential: The regulatory gene sets identified in the fruit fly have direct evolutionary homologues in mammals that are critical to neural development, raising the probability that similar circuit-simplifying frameworks exist in the human brain.Collaborative Support Infrastructure: Led by Dr. Najia Elkahlah from the lab of Associate Professor E. Josie Clowney, the study was conducted in collaboration with Villanova University, with funding from the Pew Charitable Trust, the McKnight Endowment Fund for Neuroscience, the NIH, and the NSF.<\/p>\n
Source: University of Michigan<\/p>\n
While\u00a0E. Josie Clowney\u00a0would never suggest that neuroscience is simple, a new study by her team at the University of Michigan could drastically reduce complexity in future studies.\u00a0<\/p>\n
Their work focused on instinctual behaviors in fruit flies, but it has the potential to accelerate work to better understand the neurobiology that underlies behavior and decision-making in mammals, including humans.<\/p>\n
Two sets of regulatory genes work hierarchically to group over 8,000 distinct neuron types into fewer than 200 modular structural ground plans. Credit: Neuroscience News<\/p>\n
The research establishes a new way to understand neurons, their connectivity and the behaviors they control. Within this new framework, the researchers can circumvent the conventional approach of considering each type of neuron individually and instead focus on groupings defined by shared structure and by two sets of regulatory genes.\u00a0<\/p>\n
The work was supported by the Pew Charitable Trust and the McKnight Endowment Fund for Neuroscience, with additional funding from the National Institutes of Health and U.S. National Science Foundation.<\/p>\n
While there are more than 8,000 kinds of neurons in the fruit fly cerebrum\u2014the part of its brain where instinctual behaviors are hardwired\u2014there are less than 200 major structural groups, or ground plans. Led by\u00a0Najia Elkahlah, who recently defended her doctoral thesis in the Clowney lab, the team\u2019s discoveries revealed how these ground plans get set up.<\/p>\n
There is a sort of order or hierarchy, where one set of genes coordinates the formation of the ground plan, and the other set produces small differences in shape and connectivity among neurons within each ground plan.<\/p>\n
\u201cInstead of studying all 8,000 kinds of neurons, we can instead understand how circuits work by studying these 200 modular elements that are wired together in various ways for different functions,\u201d said Clowney, associate professor in the\u00a0Department of Molecular, Cellular and Developmental Biology.<\/p>\n
These gene sets have homologues in mammals, and many of them are known to be critical in mammalian neural development. This raises the possibility of discovering similar simplifying frameworks in other organisms.<\/p>\n
\u201cAt this moment, it\u2019s not yet possible to ask if the same rules apply to analogous parts of mammalian brains, because we don\u2019t know enough about the relationships among circuits, genes or developmental programs that operate there,\u201d Clowney said. \u201cBut I feel strongly that there will be simplifying rules of some sort in the mammal as well, and that we or others will be able to discover them if we take inspiration from the way we went about making this discovery.\u201d<\/p>\n
The research was published in the journal\u00a0Nature.<\/p>\n
Taste and cease<\/p>\n
Scientists have been studying the humble fruit fly as a biological model since before they knew genes were made of DNA. That history has yielded fundamental biological discoveries, as well as a substantial body of work on which to build new ones.<\/p>\n
\u201cThe reasons we work with this animal today are because it has useful characteristics that simplify our experiments and interpretations, and because we want to take advantage of 100 years\u2019 worth of knowledge,\u201d Clowney said. \u201cIn my opinion\u2014though others in the field might disagree\u2014we don\u2019t study this animal because it is \u2018special,\u2019 but rather as a generic example of \u2018an animal.’\u201d<\/p>\n
Within the Drosophila cerebrum, researchers including Clowney had previously discovered specific neural circuits linked to specific instinctual behaviors. And this specificity helped the team discover the broader ground plans that can help simplify their quest to link molecular and cellular biology to behavior.<\/p>\n
The researchers discovered that there are two sets of regulatory genes at work. The first set controls the basic shape of the neuron, while the second set influences finer variations and connectivity.<\/p>\n
It\u2019s this first set that gives rise to the roughly 200 ground plans. Of these 200, there\u2019s one ground plan that\u2019s connected to sensing a taste and stopping a behavior. Within that ground plan, there\u2019s neural circuitry that detects unsavory taste information and quashes feeding behavior. Another circuit detects undesirable pheromonal tastes and blocks mating behavior. The team was able to identify the second set of genes that gave rise to these two distinct neural pathways and behaviors.<\/p>\n
\u201cThinking about these two sets of genes separately allowed us to relate the developmental programs to the function of circuits,\u201d Clowney said. \u201cWe identified two sets of genes that give neurons in the decision-making center of the brain their gross versus fine characteristics, and defined a new way to study these circuits.\u201d<\/p>\n
U-M research lab technician Joe Carter and doctoral students Yunzhi Lin and Yijie Pan also contributed to the study. The Clowney lab worked in collaboration with Troy Shirangi, a professor at Villanova University.<\/p>\n
Funding: Additional support for the project was provided by the U-M Advanced Genomics Core and the U-M Single Cell Spatial Analysis Program.<\/p>\n
Key Questions Answered:Q: How does reducing 8,000 neuron types down to 200 structural groups change how scientists study the brain?<\/p>\n
A: It removes immense computational complexity. Instead of analyzing thousands of individual neurons one by one, researchers can treat the brain as a network of 200 repeating, modular building blocks that are simply wired together in different combinations to execute actions.<\/p>\n
Q: How do the two different sets of genes work together to build a functional neural pathway?<\/p>\n
A: They operate in a strict hierarchy. The first set acts as a general contractor, building the basic, unrefined shape or \u201cground plan\u201d of the neuron. The second set then acts as an interior decorator, introducing the fine structural tweaks and exact wiring connections needed for a specific behavior.<\/p>\n
Q: Can this fruit fly brain discovery be applied directly to treating human neurological diseases right now?<\/p>\n
A: Not yet. While mammals share the exact same regulatory gene families, scientists do not yet know enough about mammalian circuit relationships to apply these rules directly. However, the study provides an objective framework to guide future mammalian mapping projects.<\/p>\n
Editorial Notes:This article was edited by a Neuroscience News editor.Journal paper reviewed in full.Additional context added by our staff.About this neuroscience research news<\/p>\n
Author:\u00a0Matt Davenport<\/a>
Source:\u00a0University of Michigan<\/a>
Contact:\u00a0Matt Davenport \u2013 University of Michigan
Image:\u00a0The image is credited to Neuroscience News<\/p>\n