Involvement of chitin in exoskeleton morphogenesis inDrosophila melanogaster

Abstract

Exoskeletons stabilize cell, tissue, and body morphology in many living organisms including fungi, plants, and arthropods. In insects, the exoskeleton, the cuticle, is produced by epidermal cells as a protein extracellular matrix containing lipids and the polysaccharide chitin, and its formation requires coordinated synthesis, distribution, and modification of these components. Eventually, the stepwise secretion and sorting of the cuticle material results in a layered structure comprising the envelope, the proteinaceous epicuticle, and the chitinous procuticle. To study the role of chitin during cuticle development, we analyzed the consequences of chitin absence in the embryo of Drosophila melanogaster caused by mutations in the Chitin Synthase-1 (CS-1) gene, called krotzkopf verkehrt (kkv). Our histological data confirm that chitin is essential for procuticle integrity and further demonstrate that an intact procuticle is important to assemble and to stabilize the chitin-less epicuticle. Moreover, the phenotype of CS-1/kkv mutant embryos indicates that chitin is required to attach the cuticle to the epidermal cells, thereby maintaining epidermal morphology. Finally, sclerotization and pigmentation, which are the last steps in cuticle differentiation, are impaired in tissues lacking CS-1/kkv function, suggesting that proper cuticle structure is crucial for the activity of the underlying enzymes.

Expression of the rubber‐like protein, resilin, in developing and functional insect cuticle determined using a Drosophila anti‐rec 1 resilin antibody

“…An ultrastructural examination of cuticle formation in Drosophila embryos noted that cuticle deposition is visible 12-16 hr after egg-laying (Hillman and Lesnik, 1970;Moussian et al, 2006). However, it is not until stage 17, the stage at which resilin expression is seen in this study, that chitin formation is seen in embryos (Moussian et al, 2005). Consequently, the resilin expression seen in the current study at 17-20 hr occurs well after the initiation of cuticle formation but at about the same time as chitin formation.…”

Mutation of TweedleD, a member of an unconventional cuticle protein family, alters body shape in Drosophila

“…The Drosophila larval cuticle is secreted by the underlying hypodermis at its apical face, and a new cuticle is generated for each instar. The cuticle is attached to the hypodermis at multiple anchor sites (15). Extensive cross-linking is crucial in determining the mechanical properties of the cuticle.…”

“…Mutations in Drosophila that disrupt the synthesis, modification, or deposition of chitin have been identified for a number of loci, including the genes for chitin synthase (kkv), UDP-Nacetylglucosamine pyrophosphorylase (mummy), and chitinmodifying proteins (serpentine, vermiform, knickkopf, and retroactive) (14)(15)(16)(17)(18)(19)(20)(21). In each case, gene inactivation results in a dilated or deformed cuticle.…”

dumpyinteracts with a large number of genes in the developing wing ofDrosophila melanogaster

“…6,7 Such specialized apical matrices line the external surfaces of animal bodies and internal organs and include: the surfaces of the lumen enclosed in tubular structures; the tectorial membrane of the mechanosensory epithelium of the inner ear; the zona pellucida of the oocyte; as well as the insect exoskeleton. [8][9][10][11] The Drosophila dumpy gene 12 encodes a large protein comprised of more than 300 epidermal growth factor (EGF) repeats, a class of modules found in many ECM proteins. Most of the EGF modules are interspersed with a repeat of 21 amino acids that we have termed the DPY module, and much of the Dumpy protein is composed of contiguous repeats of a three-module EGF-DPY-EGF unit.…”