Mutations in the 3' non-coding region of a no-known vector flavivirus Yokose virus increased its replication ability in mosquito C6/36 cells.

Yokose virus (YOKV) is a bat-associated no-known vector flavivirus group member. We investigated the replication ability of YOKV in mosquito-derived C6/36 cells. YOKV grew in C6/36 cells, but its kinetics of YOKV was markedly slower than those of other mosquito-borne flaviviruses. Transmission electron microscopy indicated an extremely small number of viral particles in YOKV-infected C6/36 cells. Mosquito-borne Japanese encephalitis virus prM-E-bearing chimeric YOKV failed to propagate efficiently in C6/36 cells. We isolated C6/36-adapted YOKV and identified nucleotide mutations in the adapted YOKV. Mutations detected in the 3' non-coding region of the adapted YOKV were critical for the enhanced proliferation ability of the virus. Moreover, the growth of the original and adapted YOKV in C6/36 cells was remarkably increased by shifting the culture temperature from 28 to 36 °C. Thus, our results demonstrate the potential of YOKV to propagate in mosquito cells and support its classification as a mosquito-borne flavivirus.