An anhydrobiotic cell line expressing odorant receptors shows odorant responses after dry storage
image: This figure illustrates the odor sensor function of Pv11-00443-Or47a cell line. When pentyl acetate binds specifically to the olfactory receptor Or47a, the channel formed by Or47a and co-receptor Orco opens and let calcium ions enter into the cell, where the calcium-sensitive marker GCaMP6f responds through an increase of fluorescence shown on the pictures on the right. Pv11-00443-Or47a cell line can be dried and stored at room temperature while retaining the sensing function of the odorant receptor Or47a.
Credit: National Agriculture and Food Research Organization (NARO)
Demand for odor detection is growing in diverse fields such as food security, medical diagnostics, and environmental monitoring, but current technologies face limitations. Living cells with olfactory receptors can serve as sensitive odor detectors; however, cell-based sensors require precise control of temperature, humidity, and CO₂ levels. Outside of laboratory facilities, cultured cells only survive for a short time at room temperature. Additionally, long-term storage of cell susually requires costly ultra-cold freezers or liquid nitrogen. These requirements hinder the practical implementation of cell-based olfactory sensors in portable devices and field applications. Overcoming these hurdles requires cells that can be preserved in a dry state at ambient temperatures without losing function.
Researchers at the National Agriculture and Food Research Organization (NARO) have studied the extreme desiccation tolerance in the sleeping chironomid, Polypedilum vanderplanki. This insect can survive almost complete desiccation by entering an ametabolic dormant state called anhydrobiosis. The researchers had established a cell line called Pv11, derived from this insect, that exhibits remarkable desiccation tolerance, enabling successful dry storage at room temperature for over a year. Upon rehydration, these cells resume normal metabolic activity and proliferation. Pv11 cells are unique among animal cells in their ability to be stored dry at room temperature. This unique ability makes Pv11 an ideal platform for developing artificially engineered cells that don't require continuous incubation. Meanwhile, the University of Maryland (UMD) developed a small odor sensor using olfactory cells from newts but faced difficulties in maintaining cell viability over time. To address this issue, NARO and UMD collaborated to create odor sensor cells based on Pv11 that can be stored dry at room temperature.
The research team engineered Pv11 cells to express olfactory sensing components from the fruit fly Drosophila melanogaster. The introduced genes encode: Or47a, an odorant receptor from the fruit fly that detects the compound pentyl acetate (a fruity aroma like bananas); Orco, the olfactory co-receptor that pairs with insect odorant receptors to form a functional odor-sensing complex; and GCaMP6f, an intracellular calcium-sensitive fluorescent protein that emits fluorescence when the odorant receptor is activated. The resulting clonal cell line, named Pv11-00443-Or47a, retained the desiccation tolerance of Pv11 and gained the ability to respond to the target odor. When exposed to pentyl acetate, the Pv11-00443-Or47a cells exhibited fluorescence, indicating that the introduced Or47a receptor detects odor molecules. Importantly, the cells could be dry-preserved and later rehydrated without losing this functionality.
The Pv11-00443-Or47a cells responded to pentyl acetate, with a dose-dependent increase in fluorescence intensity. The sensitivity (half-maximal effective concentration, EC50) was 3.4 µM in non-dried fresh cells, which was consistent with previously reported values (ranging from 2 µM to 30 µM) for Or47a expressed in other cell lines. Responsiveness persisted even after repeated exposures.
After two weeks of dry storage at room temperature, rehydrated cells recovered dose-dependent fluorescence responses, with an EC50 of 8.1 µM, similar to pre-drying levels. Responses were observed within 12–48 hours post-rehydration. Remarkably, the cells stored in a dry state for three years at room temperature also resumed normal odor responsiveness after rehydration.
The development of Pv11-00443-Or47a cells is a breakthrough in creating cell-based odor sensors. By demonstrating that olfactory receptor cells can be stored at room temperature without losing function, researchers have taken a significant step toward creating truly portable biosensors for odors. These cell-based odor detectors could one day be used outside of laboratories, such as in handheld devices for medical diagnoses, food quality monitoring, and environmental hazard detection. The reduced need for refrigeration and a constant power supply dramatically cuts storage and transportation costs, making biosensors much more practical in the field. The team plans to expand this technology by engineering other odorant receptors into Pv11 cells to create a repertoire of dry-storable sensory cells, each of which is tuned to a different scent. Ultimately, the researchers envision integrating these dried sensor cells into compact electronic devices to create a biohybrid “electronic nose” that can detect important odors in our surroundings.
About National Agriculture and Food Research Organization (NARO)
NARO is the core institute in Japan for conducting research and development in a wide range of fields, from basic to applied, for the development of agriculture and food industries.
For more information, visit https://www.naro.go.jp/english/index.html .