Nanopore formation in the cuticle of an insect olfactory sensillum

Abstract

Nanometer-level patterned surface structures form the basis of biological functions including superhydrophobicity, structural coloration, and light absorption [1][2][3]. In insects, the cuticle overlying the olfactory sensilla has multiple small (50-200-nm diameter) pores [4][5][6][7][8], which are 25 supposed to function as a filter that admits odorant molecules, while preventing the entry of larger airborne particles and limiting water loss. However, the cellular processes underlying the patterning of extracellular matrices into functional nano-structures remain unknown. Here we show that cuticular nanopores in Drosophila olfactory sensilla originate from a curved ultrathin film that is formed in the outermost envelope layer of the cuticle, and secreted from specialized 30 protrusions in the plasma membrane of the hair forming (trichogen) cell. The envelope curvature coincides with plasma membrane undulations associated with endocytic structures. The goretex/Osiris23 gene encodes an endosomal protein that is essential for envelope curvature, nanopore formation, and odor receptivity, and is expressed specifically in developing olfactory trichogen cells. The 24-member Osiris gene family is expressed in cuticle-secreting cells, and is 35 found only in insect genomes. These results reveal an essential requirement for nanopores for Ando et al., February 12, 2019 2 odor reception and identify Osiris genes as a platform for investigating the evolution of surface nano-fabrication in insects. Results and DiscussionThe great success of insects in spreading throughout nearly the entire terrestrial ecosystem has 5been largely due to their exoskeleton, which enabled both their adaptation to harsh environments and protection from predators. The adaptation of olfaction to airborne odorants was also key in helping insects search for food, mates, and other environmental cues, and to establish social communication [9]. Insect sensilla consist of one to several neurons and usually three supporting or auxiliary cells. The neuron(s) innervate a specialized cuticular apparatus, which often has the 10 shape of a peg or hair and is secreted by the auxiliary cells. Later in development, these cells take over other functions, e.g. secretion of the sensillum lymph that surrounds the dendrites of the neurons. In olfactory sensilla the wall of the cuticular hair shows numerous pores which are absent from sensilla serving other modalities. For volatile odorants to reach the dendrites, numerous pores ranging in diameter from 50 to 200 nm are formed in regular arrays on the 15 cuticles of the olfactory sensory organs [4][5][6][7][8]. Beneath the pores, filaments called pore tubules extend to the interior lymph and dendritic nerve endings [7,8]. These nano-scale structures are thought to allow the diffusion of small odorant molecules (0.5 to 5 nm in diameter) to reach the olfactory neurons, while preventing the entry of larger (100 to 1000 nm) airborne particles and minimizing the loss of inner lymph liquid. This selective filter system pro...

Surface coatings for solid-state nanopores

“…Coatings from fluid layers of lipids are attractive because they solve several of the most common problems in the context of nanopore recordings of proteins and other macromolecules. 107,114,295 Inspired by the lipid-coated nanopores present in the antennae of silk moths 296,297 (Fig. 12A), our group demonstrated, for instance, that lipid coatings efficiently prevent or minimize non-specific adsorption of proteins to the pore wall, eliminating clogging.…”

Modulation of the NO-cGMP pathway has no effect on olfactory responses in the Drosophila antenna

“…Olfactory sensilla are most abundant on the antenna, a major olfactory appendage in insects, and are distributed in a highly stereotyped and genetically determined fashion, such that one-or-few OSNs each expressing only oneor-few ORs innervate a sensillum shaft compartmentalizing sensory lymph bathing the neuronal dendrites (Shanbhag et al, 2000). Olfactory sensilla are lined with pores open to the external environment and function as isolated microenvironments maintained by multiple cell types wherein sensory neurons receive and transduce odor information (Steinbrecht, 1996;Ando et al, 2019). Collectively, odor information is encoded through varying degrees of combinatorial activation of specific odor-sensitive OSNs both within and across sensilla, which allows a finite number of receptors to encode an extensive variety of odor information present in the environment (Grabe and Sachse, 2017;Seki et al, 2017;Haverkamp et al, 2018).…”