Ecdysteroids hormonal roles

Some information exists on the hormonal roles of ecdysteroids in other arthropod classes (arachnids [23], myriapods [24]) and on the presence of ecdysteroids in other invertebrate phyla (helminths and annelids [25]), but further studies are required to elucidate their roles. 

Two main hypotheses have been put forward to account for the occurrence of ecdysteroids in the plant world. The first is that PEs have a hormonal role within the plant, but there is very little hard evidence in support of this hypothesis (reviewed in [26]). Alternatively, PEs participate in the defence of plants against non-adapted phytophagous invertebrates. Deterrent effects of 20E on non-adapted insect species are... 

Although, ecdysteroids occur in helminth tissue and affect a number of aspects of development, the true hormonal role of ecdysone in helminths remains to be documented. Insect juvenile hormones (JH) have also been implicated as regulators of nematode development, particularly in relationship to molting and exsheathment, but there is little analytical evidence supporting the occurrence of JH in nematodes. However, exogenously applied JH and synthetic JH analogs have been reported to alter developmental processes of nematodes (71-73). A concerted effort to apply modern analytical methods could resolve the question of the presence of insect JH in nematodes. 

In addition to their well established role in catalyzing the metabolism of a wide variety of naturally occurring and synthetic xenobiotics, cytochrome P-450-mediated mixed-function oxidases are of critical Importance in the biosynthesis and regulation of the major hormones (ecdysteroids and juvenile hormone) that control insect growth and development. The characteristics of the mixed-function oxidases involved in the synthesis of insect hormones are described and the possibility that the enzymes might represent potential targets for insect control is discussed. 

Knowledge of helminth endocrinology is rudimentary at present, though presence of a hormonal system similar to that of insects has been suggested [67]. It has been further pointed out that ecdysteroids and juvenile hormones, which control metamorphosis in insects, may also play a similar role in the growth of nematodes. This is based on the fact that ecdysteroids have been detected in nematodes, cestodes and trematodes [68-71],... 

There are several reports that cHH can inhibit the ecdysteroid synthesis by YO in vitro but that MIH cannot act as a cHH by increasing glucose concentration (see for example [108]). It was probably this multifunctionality of cHH that led to it being mistaken for MIH in certain instances. Why should cHH duplicate the role of another hormone during the moult cycle The definitive answer to this question is still not known but specific receptors for cHH (along with MIH-specific receptors) have been demonstrated, by classical membrane binding studies, to be present on the YOs of intermoult brachyuran crabs [84]. Unlike cHH, radiolabelled MIH binds only to membrane preparations of YOs and not... 

Two groups of hormones regulate development and reproduction in insects, namely the ecdysteroids and the JHs. In crustaceans too, ecdysteroids are involved in the hormonal control of growth, and a chemical compound, which is similar to the JHs of insects, is present and thought to play a role in crustacean reproduction and development. The insect JH is a species-specific acyclic sesquiterpenoid epoxide, which is synthesized in a pair of retrocerebral epithelial organs called the corpora allata (CA see Fig. 1). In decapod crustaceans, MF is the unepoxidated form of the insect JH III and it is synthesized and secreted from the MOs (see Section 3.2.4). 

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