Biology Reference
In-Depth Information
Unlike many other compounds, this new class of contaminants is defined by its biological
activity and not by physical or chemical characteristics. Indeed, many molecules with dif-
ferent chemical structures show evidence or potential evidence for endocrine disrupting
effects, and a list of 320 compounds has been compiled (European Commission 2007).
As a consequence, it is advisable to search for EDCs not by using chemical or physical
detection methods but by using screening methods that may highlight their biological
activities.
One possible way to detect EDCs is the use of genetically engineered cells in which key
receptors are expressed. For instance, the yeast estrogen screen (YES) consists of yeast
cells expressing the human receptor to estradiol and possessing a genetic construct used
to reveal the activation of the receptor. It involves the estrogen response element and a
reporter gene (a bacterial β-galactosidase enzyme) that is synthesized upon activation
(Figure 9.9). This system involving hormones (such as estradiol) and their receptors is
indeed an essential component of the endocrine system of vertebrates. The use of the YES
test can reveal the presence of estrogenic compounds able to interact with and activate
the receptor and the subsequent transcriptional activity in exposed cells. This bioassay
has been validated for the detection of a wide range of receptor agonists such as estra-
diol in 17β-estradiol, estrone, estradiol, and xenoestrogens (alkylphenols and bisphenol  A)
(Routledge and Sumpter 1996, 1997). Beside the estrogen receptor, many other nuclear
receptors can be used for screening purposes.
E 2
ERE
LacZ
Ye llow substrate
hER
Galactosidase
Red product
ER gene
Nucleus
FIGURE 9.9
Simplified diagram of gene construct used to measure estrogenic activity in YES. The gene encoding human α
receptor to estradiol (ERH) is inserted into nuclear DNA of yeast and allows receptor expression in cytoplasm.
Upon binding to receptor, estradiol (E 2 ) activates the nuclear complex that binds to response element in plasmid
(ERE) and then leads to expression of galactosidase gene ( LacZ gene). Enzyme secreted into culture medium cat-
alyzes conversion of a chromogenic yellow substrate into an easily quantifiable red product by measurement of
optical density. (From Routledge, E.J., Sumpter, J.P., Environ. Toxicol. Chem. , 15, 241-248, 1996. With permission.)
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