Analysis of Micro- and Nano-Structures of the Corneal Surface of Drosophila and Its Mutants by Atomic Force Microscopy and Optical Diffraction

Abstract

Drosophila melanogaster is a model organism instrumental for numerous biological studies. The compound eye of this insect consists of some eight hundred individual ommatidia or facets, ca. 15 µm in cross-section. Each ommatidium contains eighteen cells including four cone cells secreting the lens material (cornea). High-resolution imaging of the cornea of different insects has demonstrated that each lens is covered by the nipple arrays - small outgrowths of ca. 200 nm in diameter. Here we for the first time utilize atomic force microscopy (AFM) to investigate nipple arrays of the Drosophila lens, achieving an unprecedented visualization of the architecture of these nanostructures. We find by Fourier analysis that the nipple arrays of Drosophila are disordered, and that the seemingly ordered appearance is a consequence of dense packing of the nipples. In contrast, Fourier analysis confirms the visibly ordered nature of the eye microstructures - the individual lenses. This is different in the frizzled mutants of Drosophila, where both Fourier analysis and optical imaging detect disorder in lens packing. AFM reveals intercalations of the lens material between individual lenses in frizzled mutants, providing explanation for this disorder. In contrast, nanostructures of the mutant lens show the same organization as in wild-type flies. Thus, frizzled mutants display abnormal organization of the corneal micro-, but not nano-structures. At the same time, nipples of the mutant flies are shorter than those of the wild-type. We also analyze corneal surface of glossy-appearing eyes overexpressing Wingless - the lipoprotein ligand of Frizzled receptors, and find the catastrophic aberration in nipple arrays, providing experimental evidence in favor of the major anti-reflective function of these insect eye nanostructures. The combination of the easily tractable genetic model organism and robust AFM analysis represents a novel methodology to analyze development and architecture of these surface formations.

Diverse set of Turing nanopatterns coat corneae across insect lineages

“…The variety of these nanostructures can serve as a highly promising model, obeying the Turing mechanism of pattern formation. Insect eyes, especially those of the genetically tractable model insect Drosophila melanogaster (6,25), can therefore serve as a powerful tool to further explore the precise mechanisms of the reaction−diffusion-driven processes in living organisms, to identify the molecular components governing formation of corneal nanocoatings, and to genetically engineer novel Turing nanopatterns with novel physical properties.…”

“…Among the rare known examples of biological nanopatterns are the 3D nanostructures covering insect corneal surfaces (2). They were described in moths and butterflies and later some Dipterans as pseudoregularly spaced nipple-type protrusions, up to 200 nm in height and width (3)(4)(5)(6)(7). These nanostructures may carry antireflective, dirt-removing/ self-cleaning, and hydrophobic/antiwetting functions (2,(8)(9)(10)(11)(12).…”

Mesostructure of Ordered Corneal Nano-nipple Arrays: The Role of 5–7 Coordination Defects

“…refs 1, 2, 3, 4, 5, 6, 7, 8, 9, 10). One specific case of surface structure has drawn particular attention: the nano-nipple arrays observed on many butterfly and moth eyes.…”

Under- and over-water halves of Gyrinidae beetle eyes harbor different corneal nanocoatings providing adaptation to the water and air environments

“…Such nanostructures have been examined by means of electron and atomic force microscopy (AFM) in moths and butterflies78910 and our recent work describes the organization of nipple-formed nanostructures on the surface of the Drosophila eye11. Proposed functions of such insect nanostructures are anti-reflective, dirt-removing/self-cleaning, and hydrophobic/anti-wetting, and have inspired numerous industrial applications912131415161718.…”