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Event: 1523

Key Event Title

The KE title should describe a discrete biological change that can be measured. It should generally define the biological object or process being measured and whether it is increased, decreased, or otherwise definably altered relative to a control state. For example “enzyme activity, decreased”, “hormone concentration, increased”, or “growth rate, decreased”, where the specific enzyme or hormone being measured is defined. More help

Decrease, Cuticular chitin content

Short name
The KE short name should be a reasonable abbreviation of the KE title and is used in labelling this object throughout the AOP-Wiki. The short name should be less than 80 characters in length. More help
Decrease, Cuticular chitin content

Biological Context

Structured terms, selected from a drop-down menu, are used to identify the level of biological organization for each KE. Note, KEs should be defined within a particular level of biological organization. Only KERs should be used to transition from one level of organization to another. Selection of the level of biological organization defines which structured terms will be available to select when defining the Event Components (below). More help

Organ term

Further information on Event Components and Biological Context may be viewed on the attached pdf.The biological context describes the location/biological environment in which the event takes place.  For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable.  For individual/population events, the organ context is not applicable. More help
Organ term

Key Event Components

Further information on Event Components and Biological Context may be viewed on the attached pdf.Because one of the aims of the AOP-KB is to facilitate de facto construction of AOP networks through the use of shared KE and KER elements, authors are also asked to define their KEs using a set of structured ontology terms (Event Components). In the absence of structured terms, the same KE can readily be defined using a number of synonymous titles (read by a computer as character strings). In order to make these synonymous KEs more machine-readable, KEs should also be defined by one or more “event components” consisting of a biological process, object, and action with each term originating from one of 22 biological ontologies (Ives, et al., 2017; See List). Biological process describes dynamics of the underlying biological system (e.g., receptor signalling). The biological object is the subject of the perturbation (e.g., a specific biological receptor that is activated or inhibited). Action represents the direction of perturbation of this system (generally increased or decreased; e.g., ‘decreased’ in the case of a receptor that is inhibited to indicate a decrease in the signalling by that receptor).Note that when editing Event Components, clicking an existing Event Component from the Suggestions menu will autopopulate these fields, along with their source ID and description. To clear any fields before submitting the event component, use the 'Clear process,' 'Clear object,' or 'Clear action' buttons. If a desired term does not exist, a new term request may be made via Term Requests. Event components may not be edited; to edit an event component, remove the existing event component and create a new one using the terms that you wish to add. More help
Process Object Action
cuticle development cuticle decreased

Key Event Overview

AOPs Including This Key Event

All of the AOPs that are linked to this KE will automatically be listed in this subsection. This table can be particularly useful for derivation of AOP networks including the KE. Clicking on the name of the AOP will bring you to the individual page for that AOP. More help
AOP Name Role of event in AOP Point of Contact Author Status OECD Status
SAM depletion leading to population decline (2) KeyEvent You Song (send email) Under development: Not open for comment. Do not cite
SAM depletion leading to population decline (1) KeyEvent You Song (send email) Under development: Not open for comment. Do not cite
CHS-1 inhibition leading to mortality KeyEvent Simon Schmid (send email) Open for comment. Do not cite
SUR binding leading to mortality KeyEvent Simon Schmid (send email) Under development: Not open for comment. Do not cite


This is a structured field used to identify specific agents (generally chemicals) that can trigger the KE. Stressors identified in this field will be linked to the KE in a machine-readable manner, such that, for example, a stressor search would identify this as an event the stressor can trigger. NOTE: intermediate or downstream KEs in one AOP may function as MIEs in other AOPs, meaning that stressor information may be added to the KE description, even if it is a downstream KE in the pathway currently under development.Information concerning the stressors that may trigger an MIE can be defined using a combination of structured and unstructured (free-text) fields. For example, structured fields may be used to indicate specific chemicals for which there is evidence of an interaction relevant to this MIE. By linking the KE description to a structured chemical name, it will be increasingly possible to link the MIE to other sources of chemical data and information, enhancing searchability and inter-operability among different data-sources and knowledgebases. The free-text section “Evidence for perturbation of this MIE by stressor” can be used both to identify the supporting evidence for specific stressors triggering the MIE as well as to define broad chemical categories or other properties that classify the stressors able to trigger the MIE for which specific structured terms may not exist. More help

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) can be selected from an ontology. In many cases, individual species identified in these structured fields will be those for which the strongest evidence used in constructing the AOP was available in relation to this KE. More help
Term Scientific Term Evidence Link
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

Life Stages

The structured ontology terms for life-stage are more comprehensive than those for taxa, but may still require further description/development and explanation in the free text section. More help
Life stage Evidence
larvae High
Juvenile High
Adult Moderate

Sex Applicability

No help message More help
Term Evidence
Unspecific Moderate

Key Event Description

A description of the biological state being observed or measured, the biological compartment in which it is measured, and its general role in the biology should be provided. For example, the biological state being measured could be the activity of an enzyme, the expression of a gene or abundance of an mRNA transcript, the concentration of a hormone or protein, neuronal activity, heart rate, etc. The biological compartment may be a particular cell type, tissue, organ, fluid (e.g., plasma, cerebrospinal fluid), etc. The role in the biology could describe the reaction that an enzyme catalyses and the role of that reaction within a given metabolic pathway; the protein that a gene or mRNA transcript codes for and the function of that protein; the function of a hormone in a given target tissue, physiological function of an organ, etc. Careful attention should be taken to avoid reference to other KEs, KERs or AOPs. Only describe this KE as a single isolated measurable event/state. This will ensure that the KE is modular and can be used by other AOPs, thereby facilitating construction of AOP networks. More help

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.  

How It Is Measured or Detected

One of the primary considerations in evaluating AOPs is the relevance and reliability of the methods with which the KEs can be measured. The aim of this section of the KE description is not to provide detailed protocols, but rather to capture, in a sentence or two, per method, the type(s) of measurements that can be employed to evaluate the KE and the relative level of scientific confidence in those measurements. Methods that can be used to detect or measure the biological state represented in the KE should be briefly described and/or cited. These can range from citation of specific validated test guidelines, citation of specific methods published in the peer reviewed literature, or outlines of a general protocol or approach (e.g., a protein may be measured by ELISA).Key considerations regarding scientific confidence in the measurement approach include whether the assay is fit for purpose, whether it provides a direct or indirect measure of the biological state in question, whether it is repeatable and reproducible, and the extent to which it is accepted in the scientific and/or regulatory community. Information can be obtained from the OECD Test Guidelines website and the EURL ECVAM Database Service on Alternative Methods to Animal Experimentation (DB-ALM). ?

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 N-Acetylclucosamine (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). Another possibility is to use the non-radioactive assay developed to measure chitin synthase activity (Lucero et al. 2002; Zhang and Yan Zhu 2013). Instead of adding an enzyme extract and chitin precursors to the reaction, one could simply add homogenized chitin containing material to the reaction to quantify its chitin content.

Domain of Applicability

This free text section should be used to elaborate on the scientific basis for the indicated domains of applicability and the WoE calls (if provided). While structured terms may be selected to define the taxonomic, life stage and sex applicability (see structured applicability terms, above) of the KE, the structured terms may not adequately reflect or capture the overall biological applicability domain (particularly with regard to taxa). Likewise, the structured terms do not provide an explanation or rationale for the selection. The free-text section on evidence for taxonomic, life stage, and sex applicability can be used to elaborate on why the specific structured terms were selected, and provide supporting references and background information.  More help

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


List of the literature that was cited for this KE description. Ideally, the list of references, should conform, to the extent possible, with the OECD Style Guide ( (OECD, 2015). More help

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.

Lucero HA, Kuranda MJ, Bulik DA. 2002. A nonradioactive, high throughput assay for chitin synthase activity. Anal Biochem. 305(1):97–105. doi:10.1006/abio.2002.5594.

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.

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.

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.

Zhang X, Yan Zhu K. 2013. Biochemical characterization of chitin synthase activity and inhibition in the African malaria mosquito, Anopheles gambiae. Insect Sci. 20(2):158–166. doi:10.1111/j.1744-7917.2012.01568.x.

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.