Isolation of olfactory epithelial tissue and culture of primary olfactory epithelial organoids
To establish a culture system for olfactory epithelial organoids, we isolated olfactory epithelium from human superior turbinate tissue and embedded it in a three-dimensional Matrigel matrix (Figure 1). Building on the defined culture conditions reported by Ren et al., we validated and fine-tuned the concentrations of key growth factors, EGF, Noggin, Wnt3a, and R-pondin 1, together with the ROCK inhibitor Y-27632. This combination robustly supported clonal expansion and proliferation of olfactory epithelial organoids. Under these conditions, single olfactory epithelial cells survived in Matrigel and developed into a classic spherical organoid within 7–12 days of primary culture (Figure 2). Organoids cultured for 12 days were fixed and subjected to immunofluorescence staining for SOX2, a transcription factor critical for maintaining neural stem cell regenerative capacity, as well as GAP43 and OMP, markers of immature and mature olfactory sensory neurons, respectively. The results showed that organoids generated using our protocol co-expressed SOX2 with GAP43, and SOX2 with OMP. GAP43 expression was relatively uniform throughout the organoid, whereas OMP was predominantly localized to cells at the periphery. These findings indicate that the cultured organoids retain stemness and display a spatially organized, intermediate differentiation state (Figure 3). The three-dimensional spatial architectures and hierarchical marker distributions of these organoids can be dynamically viewed in Supplemental Video S1 (GAP43 and SOX2) and Supplemental Video S2 (OMP and SOX2). Supplemental Figure S1, an additional immunofluorescence image of mouse olfactory epithelium, confirms the specificity and reliability of the antibodies used in this study. SOX2 (red) and OMP (green) display the expected, on-target layered staining pattern in native in vivo tissue. This result strongly supports the idea that the cellular features observed in our organoid cultures reflect genuine in vitro phenotypes rather than artifacts caused by nonspecific or failed antibody staining. Nevertheless, we acknowledge that further validation is required to fully interpret the biological significance and the precise molecular dynamics of this marker overlap within the in vitro organoid system. Notably, prolonged passaging leads to morphological changes and a progressive loss of both stemness maintenance and differentiation capacity. Therefore, passaging is recommended only for early-stage expansion (e.g., passages 1–2) to obtain sufficient cells for differentiation.
Differentiation and identification of primary olfactory epithelial organoids
To induce neuronal differentiation, we formulated a specialized medium containing small molecules known to drive neurogenesis in organoid systems: the Notch signaling inhibitor LY411575, the Wnt pathway activator CHIR-99021, and retinoic acid (RA), a well-established regulator of neurodifferentiation-associated genes. By day 7 of differentiation, cells exhibiting characteristic neuronal morphology were observed adhering to the bottom of the culture dish. In the later stages of the protocol, the compact organoid structures gradually dissociated, and differentiating cells migrated outward from the three-dimensional spheres, adopting a two-dimensional, adherent growth pattern on the surface of the glass-bottom confocal dishes. Immunofluorescence staining of fixed cultures revealed that these bipolar cells, derived from primary olfactory epithelial organoids and grown as a monolayer, co-expressed OMP and the pan-neuronal marker Tuj1 (class III β-tubulin). This co-expression confirms the successful generation of mature olfactory sensory neurons from the organoid system (Figure 4). A three-dimensional visualization of these differentiated 2D-adherent neurons is provided in Supplemental Video S3.

Figure 1: Schematic diagram of the experimental workflow for establishing human olfactory epithelial organoids. Please click here to view a larger version of this figure.

Figure 2: Establishment of human olfactory epithelial organoids. Bright-field images illustrating organoid development in a specialized culture medium from day 0 to day 12. Representative images were acquired on days 3, 5, 7, and 12 using live-cell imaging. Scale bar: 100 µm. Please click here to view a larger version of this figure.

Figure 3: Immunofluorescence characterization of human olfactory epithelial organoids. Confocal microscopy images showing optical sections of three-dimensional reconstructed models of organoids immunostained for (A) the immature olfactory sensory neuron marker GAP43 (green) and the neural stem cell marker SOX2 (red), and (B) the mature olfactory sensory neuron marker OMP (green) and SOX2 (red). Scale bar: 50 µm. Please click here to view a larger version of this figure.

Figure 4: Immunofluorescence identification of human olfactory sensory neurons. Confocal microscopy image depicting differentiated cells derived from organoids exhibiting 2D adherent growth, co-stained for the mature olfactory sensory neuron marker OMP (green) and the pan-neuronal marker Tuj1 (red). Scale bar: 50 µm. Please click here to view a larger version of this figure.
Supplemental Figure S1. Validation of antibody specificity in mouse olfactory epithelium. Immunofluorescence staining of a mouse olfactory epithelium tissue section demonstrating the highly specific, on-target expression patterns of the antibodies used in this study. In the natural in vivo tissue, the neural stem cell/progenitor marker SOX2 (red) is strictly localized to the nuclei of the basal cell layer, while the mature olfactory sensory neuron marker OMP (green) is robustly expressed in the mature sensory neurons. Nuclei were counterstained with DAPI (blue).Please click here to download this file.
Supplemental Video S1. Three-dimensional reconstruction of an olfactory epithelial organoid (GAP43 and SOX2). Confocal Z-stack 3D reconstruction video (acquired at 40X magnification) demonstrating the spatial distribution of the immature olfactory sensory neuron marker GAP43 (green) and the neural stem cell marker SOX2 (red) within the spherical structure of the organoid.Please click here to download this file.
Supplemental Video S2. Three-dimensional reconstruction of an olfactory epithelial organoid (OMP and SOX2). Confocal Z-stack 3D reconstruction video (acquired at 40X magnification) demonstrating the spatial distribution of the mature olfactory sensory neuron marker OMP (green) and the neural stem cell marker SOX2 (red) within the spherical structure of the organoid.Please click here to download this file.
Supplemental Video S3. Three-dimensional visualization of differentiated olfactory sensory neurons (OMP and Tuj1). Confocal Z-stack 3D reconstruction video (acquired at 20X magnification) showing the morphological features of differentiated cells derived from the organoids. These adherent cells co-express the mature olfactory sensory neuron marker OMP (green) and the pan-neuronal marker Tuj1 (red).Please click here to download this file.