At the core of the investigation lies the DA1-ORN to VA1v-PN pathway, a discrete olfactory circuit segment traditionally understood to maintain exclusive synaptic partnerships. The team harnessed the genetic LexA/LexAop system to express the calcium indicator GCaMP7b specifically in VA1v projection neurons, enabling real-time visualization of intracellular calcium fluctuations—used here as a faithful proxy for neuronal activity. Concurrent expression of the red fluorescent protein tdTomato in DA1-ORNs provided a robust anatomical marker to verify the rewiring at high resolution.

The sophistication of their approach was exemplified by two-photon excitation microscopy, which allowed precise measurement of calcium dynamics within the dendritic compartments of VA1v-PNs in living tethered flies. This methodology, combined with carefully controlled odor stimulation protocols, provided an unparalleled window into the functional consequences of synaptic reorganization induced by cell-surface molecular code manipulation.

Olfactory stimulation was delivered using two pheromones with well-characterized receptor affinities: 11-cis-vaccenyl acetate (cVA), which specifically activates DA1-ORNs, and palmitoleic acid (PA), known to activate VA1v-ORNs. In wild-type flies, GCaMP7b fluorescence intensities in VA1v-PNs increased in response to PA, aligning with established neuronal selectivity, while exposure to cVA led to a suppression of activity, indicative of lateral inhibitory mechanisms mediated by local interneurons within the antennal lobe circuitry.

Remarkably, in flies engineered to exhibit the DA1-ORN to VA1v-PN rewiring, VA1v-PNs displayed robust activation not only to PA but also to cVA. This functional gain of cVA responsiveness underscores the formation of excitatory synaptic connections between DA1-ORN axons and VA1v-PN dendrites, a phenomenon actively quantified by increases in calcium signal intensity. These findings imply that the engineered rewiring confers cross-activation, fundamentally altering the odor coding landscape within the antennal lobe.

The inhibitory response traditionally observed in VA1v-PNs to cVA in wild-type flies results from lateral inhibition orchestrated by various local interneurons, which sculpt the olfactory processing network’s dynamic range and sensitivity. Intriguingly, examination of the responses to odours outside the typical activation profiles of DA1 or VA1v ORNs revealed largely conserved inhibitory patterns in both wild-type and rewired flies. This persistence suggests that while the direct ORN-PN connectivity was modified, the broader interneuronal inhibitory network remained intact.

From a mechanistic standpoint, the work leverages the conserved cholinergic neurotransmitter system that mediates excitatory ORN-PN synapses across different olfactory pathways. By altering the cell-surface combinatorial molecular codes that guide axonal targeting and synaptic specificity, the study provides compelling evidence that molecular identity cues are instrumental in defining, yet also flexible within, the neural wiring blueprint.

Beyond technical prowess, the study addresses longstanding questions about the plasticity of hardwired sensory circuits in adult animals. While developmental plasticity in olfactory networks is well-documented, the capacity to rewire existing synaptic connections via molecular manipulation offers profound insights into circuit adaptability, potentially informing strategies for neuroregenerative therapies and artificial sensory system design.

This research also underscores the nuanced balance between anatomical rewiring and functional circuit output. The coexistence of newly formed excitatory connections alongside preserved inhibitory interactions implies a modular approach to circuit remodeling without wholesale disruption of network homeostasis. Whether such rewiring affects olfactory behavior or perception remains an enthralling avenue for future investigations.

Using state-of-the-art, genetically encoded calcium sensors and fluorescent markers allowed for simultaneous anatomical and functional verification of rewired synapses within intact neural tissue, reinforcing the importance of multimodal imaging in neuroscience research. The combination of targeted genetic tools and two-photon microscopy constitutes a powerful platform for dissecting intricate circuit modifications in vivo.

Moreover, these findings challenge the dogma that olfactory receptor neuron projections to defined glomeruli are immutable, implicating that combinatorial expression patterns on the cell surface can effectively redirect axonal targeting and reshape odor representation maps. This capability opens possibilities for reprogramming sensory circuits to alter perception or behavior in a precise, circuit-specific manner.

While the study is focused on Drosophila melanogaster, the broader implications resonate across taxa, given the evolutionary conservation of many molecular guidance mechanisms and neurotransmitter systems. Such cross-species relevance elevates the significance of this research for the wider neuroscience community, inspiring approaches to modulate neural connectivity in diverse contexts.

In sum, the meticulous work of Lyu et al. unveils a new dimension of neural circuit flexibility by demonstrating that peripheral olfactory neurons can be coerced into forming ectopic, functional synapses with projection neurons typically outside their domain. This paradigm-shifting discovery redefines our understanding of neural specificity and plasticity within sensory systems and holds vast potential for unraveling the principles of brain wiring and reconfiguration.

Subject of Research: Neural circuit plasticity and olfactory system rewiring in Drosophila melanogaster

Article Title: Rewiring an olfactory circuit by altering cell-surface combinatorial code

Article References:
Lyu, C., Li, Z., Xu, C. et al. Rewiring an olfactory circuit by altering cell-surface combinatorial code. Nature (2025). https://doi.org/10.1038/s41586-025-09769-3

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41586-025-09769-3

Bone marrow, the soft, spongy tissue nestled inside bones, plays a pivotal role in hematopoiesis—the process of blood cell formation—and is crucial for immune system maintenance. Despite its biological importance, detailed investigation of bone marrow microanatomy has been severely limited by its gelatinous nature combined with the rigid encasement provided by the surrounding bone matrix. Traditional imaging modalities have had to contend with either the destructive dissociation of the tissue, as in flow cytometry, or limited multiplex capability in fluorescence microscopy, constraining the scope of molecular and cellular markers that could be concurrently assessed.

In response to these challenges, the Indiana University team harnessed the power of Phenocycler 2.0™, an advanced multiplex imaging platform that allows for high-dimensional, spatially resolved analysis of tissue specimens. This next-generation instrument was deployed to chart an expansive array of 25 distinct cellular markers within intact mouse bone marrow tissue sections, enabling precise cellular phenotyping without disrupting the native tissue architecture. This level of multiplexing and preservation of tissue context has never before been achieved in bone marrow research, marking a pivotal advance in the field.

The study, which appears in the prestigious journal Leukemia, represents a notable technical leap, as stated by co-lead author Dr. Sonali Karnik. The assistant research professor of orthopedic surgery at IU School of Medicine emphasized that this unique imaging approach not only captures the intricate spatial relationships among diverse bone marrow cell populations but also accesses valuable stem cell niches critical to regenerative medicine and immune function. The technique circumvents the need to mechanically deconstruct tissue for analysis, thereby maintaining native cellular interactions central to understanding disease pathogenesis and therapeutic response.

Prior analytical methods such as flow cytometry, though extremely robust in quantifying cell populations, inherently require cell suspension preparation that destroys the tissue microenvironment and spatial context. Meanwhile, conventional fluorescence imaging techniques typically allow for only a limited number of markers—usually up to three—to be visualized simultaneously. The new multiplex imaging methodology leveraging Phenocycler 2.0 expands this capability nearly ten-fold, offering a comprehensive molecular fingerprint of the bone marrow ecosystem. This technological advantage holds the potential to decode complex pathological mechanisms that underpin hematologic diseases with greater precision.

Importantly, the IU researchers are pioneers in translating the Phenocycler 2.0 platform for mouse bone marrow analysis. While the tool has been previously utilized to image organs such as the spleen and kidney, its application within the dense and delicate bone marrow milieu posed unique challenges. The successful adaptation of this technology opens new avenues for preclinical research, especially in murine models that serve as fundamental platforms for studying human disease mechanisms and therapeutic interventions.

Co-senior author Dr. Reuben Kapur, who directs the Herman B Wells Center for Pediatric Research, highlighted the translational implications of the technique. Mouse models are central to biomedical research due to their genetic tractability and physiological relevance. By enabling detailed, multiplexed imaging of bone marrow in these models, this innovation provides researchers with a potent investigative tool to dissect complex diseases such as leukemia, autoimmune disorders, and other marrow-associated conditions. This capability will likely expedite drug discovery efforts and advance personalized therapeutic approaches.

In anticipation of the broader scientific and commercial applications of this imaging modality, the Indiana University Innovation and Commercialization Office has filed a provisional patent to protect this novel technology. Concurrent with commercialization efforts, research is underway to expand the marker panel to integrate additional components such as bone matrix proteins, neuronal elements, muscular structures, and expanded immune and signaling cell populations. This multifaceted approach seeks to deepen the biological insight obtainable from bone marrow studies, potentially enriching therapeutic target discovery.

The technical sophistication of Phenocycler 2.0 lies in its ability to conduct cyclic immunofluorescence staining and imaging, which involves repetitively labeling tissue with antibodies against different epitopes, imaging, and then chemically or photochemically stripping the labels to allow subsequent rounds. This iterative method enables the detection of an extensive array of biomarkers on the same tissue section with remarkable spatial resolution, preserving cellular and subcellular details. Such multiplex capacity is essential to unravel the heterogeneity and intercellular communications within the bone marrow niche.

Looking forward, the detailed spatial profiling enabled by this technology may offer critical insights into how microenvironmental interactions influence disease initiation, progression, and treatment resistance in hematologic malignancies and immune disorders. Researchers will be better equipped to characterize the dynamic interplay among hematopoietic stem cells, progenitor populations, stromal support cells, and infiltrating immune cells, leveraging the spatial context to inform novel diagnostic and therapeutic strategies.

The collaborative research team contributing to this study includes a multidisciplinary cadre of scientists and clinicians, each bringing specialized expertise in orthopedics, hematology, pathology, and imaging sciences. Their combined efforts underscore the interdisciplinary framework required for such technical innovations to materialize and deliver meaningful biomedical impact. Furthermore, financial support from the National Institutes of Health underpins the project’s significance and potential to drive forward the frontiers of biomedical imaging.

These advancements at Indiana University School of Medicine, the nation’s largest medical school recognized for its extensive NIH funding and innovative research, highlight its leadership in pioneering tools that bridge technological innovation and clinical relevance. Their success in developing a non-destructive, multiplexed bone marrow imaging platform not only opens new research vistas but also sets a precedent for how tissue-based analyses can evolve in the age of high-parameter imaging and precision medicine.

As the scientific community seeks to unravel the complexity of human diseases from their earliest molecular events, methodologies like the one developed at IU represent a vital step forward. This multiplex approach offers unprecedented granularity, spatial context, and biological breadth, allowing researchers to visualize the nuanced cellular environment within bone marrow, ultimately fostering breakthroughs that can translate into improved treatments and patient outcomes.

Subject of Research: Bone marrow imaging and analysis using advanced multiplex imaging technology.

Article Title: Multiplex imaging of murine bone marrow using Phenocycler 2.0™

News Publication Date: 11-Apr-2025

Web References:
Leukemia Journal Article
Indiana University School of Medicine
IU Cooperative Center of Excellence in Hematology

Image Credits: Tim Yates, IU School of Medicine

Keywords: Bone marrow, Blood diseases, Bone diseases, Autoimmune disorders, Cancer treatments