Cuticle synthesis

Many details of the anatomy and biochemistry of insect development from egg to adult are known. Growth and development are strictly regulated by hormones, and hormone concentration, relative and absolute, is vital for this to proceed correctly. The hormones control cuticle synthesis, molting, sexual maturation, color differentiation, reproduction, etc. 

Interfering with tyrosinase, an enzyme of cuticle synthesis in insects (D 22.2.5)... 

The solubility in water with 1% DMSO allows a maximum concentration of 100 iM. The studied compounds were without effect on seedlings at this concentration. These results show that specific effects of the products on Vida faba cuticle synthesis may be obtained in the presence of a maximum deposit of product which was 3 nmoles dm"2 for monensin, 500 nmoles dm-2 for EPTC and 300 nmoles dm 2 for the fatty acid analogues. 

Figure 2. Temporal profile of DDC enzyme activity during Drosophila development. Note the major peaks of DDC induction during late embryo-genesis, at pupariation, and at the time of eclosion of the adult from the pupal case. At these developmental times when there is extensive synthesis and hardening of cuticle, the induced DDC in the hypoderm is involved in this process. Levels of DDC in the CNS show much less developmental variation (Hirsh, 1986). Figure adapted from Hirsh, 1986.

Drosophila Ddc is expressed primarily in the CNS and the hypoderm, the epithelial layer of the fly that secretes the cuticle. In the CNS, Ddc is expressed in a small subset of neurons that produce either dopamine or serotonin (Budnik and White, 1988 Valles and White, 1988). In the hypoderm, Ddc expression leads to synthesis of dopamine, which is further metabolized into quinones that have a vital function in the cross-linking, hardening, and pigmentation of the fly cuticle (Wright, 1987). The developmental profile of DDC activity in these two tissues is quite different (Hirsh, 1986). DDC is first detected during late embryo-... 

All nematodes undergo four post-embryonic moults, characterized by the synthesis of a new extracellular proteinaceous cuticle from the predom-inandy syncytial hypodermis. Five separate cuticles are synthesized by all nematodes by a process referred to as moulting or ecdysis. 

Capsaicinoids start to accumulate 20 days post anthesis and synthesis usually persists through Suit development [59, 62,73], The site of synthesis and accumulation of the capsaicinoids is the epidermal cells of the placenta in the fmit (Fig. 8.5) [60, 72, 73], Ultimately, the capsaicinoids are secreted extracellularly into receptacles between the cuticle layer and the epidermal layer of the placenta [74]. These receptacles of accumulated capsaicinoids are macroscopically visible as pale yellow to orange droplets or blisters on the placenta of many chile types (Fig. 8.5). 

Schal, C., Sevala, V. L Young, H. P. and Bachmann, J. A. S. (1998). Sites of synthesis and transport pathways of insect hydrocarbons cuticle and ovary as target tissues. American Zoologist 38 382-393. 

The presence of catechols and more complex, oxidizable polyphenols in nature is widespread, and their functions are not limited to chemical defense. However, biological control of their oxidation is usually a feature of their function, as it is (1) in melanin synthesis,3 (2) in immunologically mediated delayed-type hypersensitivity responses,4 (3) in the hardening or curing of arthropod secretions (for example, as in the surface attachment adhesives of the barnacle and in tanning of the cuticle in insects),5 as well as (4) in defensive mechanisms in higher plants, particularly in the unleashing of immediate necrotrophic responses.6... 

Both compounds included here are experimental and in each case the pyridine is a benzene replacement and is not essential for the activity. The urea (103) (79SAP7802440) is a member of a highly active series that kill insects by disrupting the formation of new insect cuticle, through inhibition of chitin synthesis. The cyclopropane ester (104) (78GEP2810881) is a heterocyclic analogue of the pyrethroid insecticides, an extremely successful new class which are active on a wide range of insects. 

Ecdysone stimulates the synthesis of RNA in tissues. Visual demonstration of the effect is provided by its action on polytene chromosomes of fly larvae (Fig. 26-14).361 Fifteen minutes after the application of ecdysone, a puff is induced on one band of the chromosome a second puff forms at a later time while a preexisting puff diminishes. Thus, like steroid hormones in mammals, ecdysone appears to have a direct controlling effect on transcription. The cuticle-shedding process (ecdysis) is initiated by the brain peptide eclosian. However, the brain may be responding to the ecdysis-triggeiing hormone, a peptide that is secreted by a series of epitracheal glands located in various segments of the body.362... 

Once the medicinal properties of I and II were appreciated, the inevitable synthesis of carbamate analogs followed. The anticholinesterase activity of physostigmine- and eserine-related synthetics suggested their possible use as Insecticides but tests of early compounds failed, due to the quaternary ammonium barrier to penetration of the insect cuticle present in them. 

St. Leger, R. J., Butt, T. M., Staples, R. C., and Roberts, D. W. (1989). Synthesis of proteins including a cuticle-degrading protease during differentiation of the entomopathogenic fungus Metarhizium anisopliae. Experimental Mycology, 13, 253-262. 

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