Enhanced sensitivity of chimeric insect olfactory co-receptors for detecting odorant molecules.

Insect olfactory receptors (ORs) are seven-transmembrane domain ion channels that function by forming heteromeric complexes with olfactory receptor co-receptors (Orcos). In this study, we investigated the potential for enhancing sensitivity of odor detection and responsivity through genetic modification of Orcos, considering its wider application in odor sensing. First, we measured the intensity of response to 1-octen-3-ol for the mosquito Aedes aegypti OR (AaOR8) when complexed individually with an Orco from the same mosquito (AaOrco), the honeybee Apis mellifera (AmOrco), the silkworm Bombyx mori (BmOrco), or the fruit fly Drosophila melanogaster (DmOrco). Relative to the other Orcos, AmOrco demonstrated higher sensitivity and responsivity, with a 1.8 to 21-fold decrease in the half-maximal effective concentration (EC50) and a 1.6-8.8-fold increase in the maximal effect (Emax), respectively. Furthermore, AmOrco co-expressed with AaOR10, BmOR56, or DmOR47a showed higher sensitivity and responsivity than AaOrco, BmOrco, or DmOrco co-expressed with their respective ORs. To further increase sensitivity and responsivity, we engineered chimeric Orcos by fusing AmOrco with DmOrco, considering the domain characteristics of Orcos. The response to 1-octen-3-ol was evaluated for AaOR8 when complexed individually with AmOrco, as well as for a mutant that combines DmOrco from the N-terminal (NT) to the C-terminal region of the fourth transmembrane domain (TM4) with the region of AmOrco following TM4 (Dm[NT-TM4]AmOrco). When compared to AmOrco, Dm(NT-TM4)AmOrco showed higher sensitivity and responsivity, with a 1.4-fold decrease in the EC50 and a 1.4-fold increase in the Emax, respectively. In addition, Dm(NT-TM4)AmOrco co-expressed with either DmOR47a or BmOR56 demonstrated higher sensitivity and responsivity than AmOrco co-expressed with their respective ORs. These results suggest that AmOrco could be a relatively more sensitive Orco, and further enhancement of sensitivity and responsivity could be achieved through recombination with heterologous Orcos near the TM4 of AmOrco.

Suppression of the Epithelial-Mesenchymal Transition and Maintenance of the Liver Functions in Primary Hepatocytes through Dispersion Culture within a Dome-Shaped Collagen Matrix.

Primary hepatocytes are valuable for studying liver diseases, drug-induced liver injury, and drug metabolism. However, when cultured in a two-dimensional (2D) environment, primary hepatocytes undergo rapid dedifferentiation via an epithelial-mesenchymal transition (EMT) and lose their liver-specific functions. On the other hand, a three-dimensional (3D) culture of primary hepatocyte organoids presents challenges for analyzing cellular functions and molecular behaviors due to strong cell-cell adhesion among heterogeneous cells. In this study, we developed a novel dispersion culture method of hepatocytes within a dome-shaped collagen matrix, overcoming conventional limitations. The expression levels of EMT-related genes were lower in rat primary hepatocytes cultured using this method for 4 d than in cells cultured using the 2D method. Furthermore, albumin production, a marker of liver function, declined sharply in rat primary hepatocytes cultured in two dimensions from 6.40 µg/mL/48 h on day 4 to 1.35 µg/mL/48 h on day 8, and declined gradually from 4.92 µg/mL/48 h on day 8 to 3.89 µg/mL/48 h on day 14 in rat primary hepatocytes cultured using our new method. These findings indicate that the newly developed culture method can suppress EMT and maintain liver functions for 14 d in rat primary hepatocytes, potentially expanding the utility of primary hepatocyte cultured by using conventional 3D methods.