Key Event Title
|Level of Biological Organization|
Key Event Components
Key Event Overview
AOPs Including This Key Event
|AOP Name||Role of event in AOP|
|SAM depletion leading to population decline (2)||KeyEvent|
|SAM depletion leading to population decline (1)||KeyEvent|
|CHS-1 inhibition leading to mortality||KeyEvent|
|SUR binding leading to mortality||KeyEvent|
|Pieris brassicae||Pieris brassicae||High||NCBI|
|Lucilia cuprina||Lucilia cuprina||High||NCBI|
|Bombyx mori||Bombyx mori||High||NCBI|
|Artemia salina||Artemia salina||High||NCBI|
|Ostrinia nubilalis||Ostrinia nubilalis||High||NCBI|
Key Event Description
This key event describes the decrease in cuticular chitin content. Chitin is a major part of the arthropod cuticle and therefore also responsible for its integrity (Reynolds 1987; Muthukrishnan et al. 2012). The cuticle is the exoskeleton of arthropods and has manifold functions, it protects organisms from predators, loss of water, acts as a physical barrier against microbial pathogens and provides support for muscular function (Vincent and Wegst 2004). Hence, cuticular chitin is also indispensable for the development of arthropods, as an immaculate cuticle is required for proper molting and therefore also for the growth of an organism.
During molting, the newly secreted cuticle is subject to mechanical stress associated and therefore needs to possess enough structural and functional integrity. The ecdysis motor program, which constitutes the behavioral part of the cuticle shedding requires the newly secreted cuticle to possess a certain strength to support for muscular force in order to shed the old cuticle (Ewer 2005). Cuticular integrity is also important after ecdysis, as insects and crustaceans expand their new cuticle by increasing internal pressure by swallowing air and water, respectively. This happens in order to expand and provide stability to the new cuticle until it is hardened (tanned) (Clarke 1957; Lee 1961; Dall et al. 1978; deFur et al. 1985).
How It Is Measured or Detected
Several ways to determine cuticular chitin are described in the literature. Some of them are based on the determination of amino sugars after digestion or hydrolysis of chitin. For example, after the digestion of chitin by a bacterial chitinase, the GlcNAc amount can be determined colorimetrically by a modified Morgan-Elson assay (Reissig et al. 1955; Arakane et al. 2005). Alternatively, one can also quantify glucosamine colorimetrically after deacetylation and hydrolysis of chitin (Lehmann and White 1975; Zhang and Zhu 2006).
There also exists an approach based on the detection of fluorescence after staining with calcofluor white. In this assay, no treatment of the samples is necessary, the detection is carried out in homogenates of the respective organisms as calcofluor white directly binds to chitin (Henriques et al. 2020).
Chitin can also be quantified using radioactively labelled precursors (e.g. 14C-UDP-GlcNAc) which are incorporated into in vitro cultured integument pieces or into the cuticle of whole organisms (Gijswijt et al. 1979; Turnbull and Howells 1982; Calcott and Fatig 1984; Gelman and Borkovec 1986).
Domain of Applicability
Taxonomic: Effect data for the occurrence of this KE exist from Pieris brassicae, Lucilia cuprina, Bombyx mori, Artemia salina and Ostrinia nubilalis, defining its taxonomic applicability. Most likely, this KE is applicable to the whole phylum of arthropods, as they all rely on chitin as part of their exoskeleton.
Life stage: This KE is applicable for organisms synthesizing chitin in order to grow and develop, namely larval stages of insects and all life stages of crustaceans and arachnids.
Sex: This KE is applicable to all sexes.
Chemical: Substances known decrease the cuticular chitin content are of the family of pyrimidine nucleosides (e.g. polyoxin D and nikkomycin Z) (Gijswijt et al. 1979; Turnbull and Howells 1982; Calcott and Fatig 1984; Zhuo et al. 2014; Osada 2019). There also exists evidence for phthalimides (captan, captafol and folpet) to to decrease the cuticular chitin content in vitro (Gelman and Borkovec 1986). However, as these substances are known to covalently bind to thiol groups in proteins (Lukens and Sisler 1958), it is not clear if the inhibition is due to specific CHS-1 inhibition or due to unspecific protein binding.
Evidence for Perturbation by Stressor
Arakane Y, Muthukrishnan S, Kramer KJ, Specht CA, Tomoyasu Y, Lorenzen MD, Kanost M, Beeman RW. 2005. The Tribolium chitin synthase genes TcCHS1 and TcCHS2 are specialized for synthesis of epidermal cuticle and midgut peritrophic matrix. Insect Mol Biol. 14(5):453–463. doi:10.1111/j.1365-2583.2005.00576.x.
Calcott PH, Fatig RO. 1984. Inhibition of Chitin metabolism by Avermectin in susceptible Organisms. J Antibiot (Tokyo). 37(3):253–259. doi:10.7164/antibiotics.37.253.
Clarke KU. 1957. On the Increase in Linear Size During Growth in Locusta Migratoria L. Proc R Entomol Soc London Ser A, Gen Entomol. 32(1–3):35–39. doi:10.1111/j.1365-3032.1957.tb00361.x.
Dall W, Smith DM, Press B. 1978. Water uptake at ecdysis in the western rock lobster. J Exp Mar Bio Ecol. 35(1960). doi:10.1016/0022-0981(78)90074-6.
deFur PL, Mangum CP, McMahon BR. 1985. Cardiovascular and Ventilatory Changes During Ecdysis in the Blue Crab Callinectes Sapidus Rathbun. J Crustac Biol. 5(2):207–215. doi:10.2307/1547867.
Ewer J. 2005. How the ecdysozoan changed its coat. PLoS Biol. 3(10):1696–1699. doi:10.1371/journal.pbio.0030349.
Gelman DB, Borkovec AB. 1986. The pharate adult clasper as a tool for measuring chitin synthesis and for identifying new chitin synthesis inhibitors. Comp Biochem Physiol Part C, Comp. 85(1):193–197. doi:10.1016/0742-8413(86)90073-3.
Gijswijt MJ, Deul DH, de Jong BJ. 1979. Inhibition of chitin synthesis by benzoyl-phenylurea insecticides, III. Similarity in action in Pieris brassicae (L.) with Polyoxin D. Pestic Biochem Physiol. 12(1):87–94. doi:10.1016/0048-3575(79)90098-1.
Henriques BS, Garcia ES, Azambuja P, Genta FA. 2020. Determination of Chitin Content in Insects: An Alternate Method Based on Calcofluor Staining. Front Physiol. 11(February):1–10. doi:10.3389/fphys.2020.00117.
Lee RM. 1961. The variation of blood volume with age in the desert locust (Schistocerca gregaria Forsk.). J Insect Physiol. 6(1):36–51. doi:10.1016/0022-1910(61)90090-7.
Lehmann PF, White LO. 1975. Chitin Assay Used to Demonstrate Renal Localization and Cortisone-Enhanced Growth of Aspergillus fumigatus Mycelium in Mice. Infect Immun. 12(5):987–992.
Lukens RJ, Sisler HD. 1958. 2-Thiazolidinethione-4-carboxylic acid from the reaction of captan with cysteine. Science (80- ). 127(3299):650. doi:10.1126/science.127.3299.650.
Muthukrishnan S, Merzendorfer H, Arakane Y, Kramer KJ. 2012. Chitin Metabolism in Insects. Elsevier B.V. http://dx.doi.org/10.1016/B978-0-12-384747-8.10007-8.
Osada H. 2019. Discovery and applications of nucleoside antibiotics beyond polyoxin. J Antibiot (Tokyo). 72(12):855–864. doi:10.1038/s41429-019-0237-1. http://dx.doi.org/10.1038/s41429-019-0237-1.
Reissig JL, Strominger JL, Leloir LF. 1955. A modified colorimetric method for the estimation of N-acetylamino sugars. J Biol Chem.:959–966.
Reynolds SE. 1987. The cuticle, growth and moulting in insects: The essential background to the action of acylurea insecticides. Pestic Sci. 20(2):131–146. doi:10.1002/ps.2780200207.
Turnbull IF, Howells AJ. 1982. Effects of several larvicidal compounds on chitin biosynthesis by isolated larval integuments of the sheep blowfly Lucilia cuprina. Aust J Biol Sci. 35(5):491–504. doi:10.1071/BI9820491.
Vincent JFV, Wegst UGK. 2004. Design and mechanical properties of insect cuticle. Arthropod Struct Dev. 33(3):187–199. doi:10.1016/j.asd.2004.05.006.
Zhang J, Zhu KY. 2006. Characterization of a chitin synthase cDNA and its increased mRNA level associated with decreased chitin synthesis in Anopheles quadrimaculatus exposed to diflubenzuron. Insect Biochem Mol Biol. 36(9):712–725. doi:10.1016/j.ibmb.2006.06.002.
Zhuo W, Fang Y, Kong L, Li X, Sima Y, Xu S. 2014. Chitin synthase A: A novel epidermal development regulation gene in the larvae of Bombyx mori. Mol Biol Rep. 41(7):4177–4186. doi:10.1007/s11033-014-3288-1.