New insights into the emergence of surface nanostructures have emerged from a study of how flies smell. The research could open up new biomimetic materials and other developments. [Ando, T. et al., Curr. Biol. (2019) DOI: 10.1016/j.cub.2019.03.043]

Natural and elaborate surface structures with interesting properties are well known to materials science and offer great inspiration. The iridescence of the wonderful tail feathers of the male peacock, the water-repellency of the lotus leaf, the photonic effects of the scales on the Morpho butterflies wings. The properties of such natural surfaces generally arise because of the nanoscopic scale on which the features exist.

Now, Shigeo Hayashi of the RIKEN Center for Biosystems Dynamics Research (BDR) in Japan, and colleagues have gained new insights into how the nanopores that allow the fruit fly to detect chemicals in the air are generated. The team has identified the gene responsible for the development of this natural porous fabric which is akin to a breathable fabric like Gore-tex.

Insects have sensilla, olfactory organs, on their antennas the surface of which has tiny nanoscopic pores, some 50 to 200 nanometers across. Those nanopores work as filters allowing odorant molecules and pheromones in for detection but precluding the entry of larger airborne particles. They also prevent loss of liquid from the interior.

Hayashi and colleagues hope to understand how these pores develop and so have investigated the developing pupa of the fruit fly, Drosophila melanogaster, in detail using transmission electron microscopy (TEM). The researchers found that the cuticular nanopores in the fruit fly's olfactory sensilla originate from a curved ultrathin film. This film is formed in the outermost envelope layer of the cuticle. The team also showed that this is secreted from specialized protrusions in the plasma membrane of the hair-forming (trichogen) cell. The curvature of the envelope coincides with undulations in the plasma membrane associated with structures within the cells.

With this information in hand, the team then investigated the genetics behind the formation of pores. They used genome sequencing and identified a gene, named gore-tex, which they explain is responsible for the formation of the pores. When they carried out knockout experiments that disable this gene, the fly lost its ability to detect odorant molecules but its biology was otherwise unaffected.

"Our study revealed the elements required for the development of nanopores to allow odor reception, and identified Osiris genes as a platform for investigating the evolution of surface nano-fabrication in insects," Hayashi explains. "We hope that studies like this will help us understand how nature builds these fascinating nanostructures that allow living creatures to acquire many specialized functions." Such research will inevitably inspire materials scientists looking for novel nanostructures with properties that might useful in separation science, sensors, and other areas.