Lipid droplets in the pheromone gland of wild silkmoth Bombyx mandarina

抄録

Bombykol is the first sex pheromone that was chemically identified from silkmoth Bombyx mori. To date, the biosynthetic mechanism of bombykol in the pheromone gland (PG) of B. mori has been intensively investigated. The most prominent characteristic of pheromone-producing cells in B. mori is the abundance of cytoplasmic lipid droplets (LDs). During sex pheromone biosynthesis, LDs in the PG have been implicated to play important roles as lipid storage organs for the pheromone precursors. However, the presence of LDs in other moth species except for B. mori remains poorly described. Thus, we hypothesized that LD formation in the PG of B. mori may be caused by corpulence under domestication resulting from the loss of flight through hybridization for generating commercial lines with enlarged body size. To verify our hypothesis, we explored LDs in the PG of a closely related species, B. mandarina. A bright-field microscopic observation of B. mandarina PG revealed the presence of candidate LDs with a diameter of approximately 10μm. Fluorescent microscopy revealed that these candidate LDs could be stained with a Nile red. Subsequent observation under a confocal laser-scanning microscopy confirmed that these candidate LDs were localized in the cytoplasm of the sex pheromone-producing cells in the PG of B. mandarina, indicating that these candidates were LDs. Therefore, we concluded that LD formation is a conserved trait between B. mori and B. mandarina, and the formation of LDs in B. mori may be not caused by domestication.