Figure 10

A suggested cross-talk between Aryl hydrocarbon receptor (Ahr) and Er1 signaling pathways. A cross talk is suggested by the expression of the following genes: esr1, vtg1 and vtg3, nuclear receptor subfamily 2f1 (nr2f1; similar to human COUP-TF), ahr-nuclear translocator2 (arnt2), cyp1a1 and ahr2. The Nuclear receptor 2f1 (Nr2f1) inhibits E2-induced reporter gene and regulates transcription activated by the Ahr. Upon binding of the ligand, Ahr is translocated into the nucleus where it dimerized with the Ahr nuclear translocator (Arnt). The Ahr/Arnt complex binds with high affinity to specific xenobiotic response elements (XREs) and activates the transcription of enzymes such as Cyp1a1 (Cytochrome p450 1a1), involved in the metabolism of many drugs and xenobiotics. A negative correlation was found between the expression patterns of the genes esr1 (estrogen receptor 1), vtg1 and vtg3 (vitellogenin1 and vitellogenin3, respectively) and the genes nr2f1, arnt2, cyp1a1 and ahr2. The following expression patterns were found: i) esr1, vtg1 and vtg3 were highly expressed in vitellogenic females and E2-treated males; ii) ahr2 and arnt2 were highly expressed in control males and showed higher (though not significantly different) expression levels in non-vitellogenic females than vitellogenic females; iii) cyp1a1 was highly expressed in non-vitellogenic females and control males and significantly down-regulated by E2 treatment, and iv) nr2f1 was highly expressed in non-vitellogenic females and showed higher expression levels (though the difference was not significant) in control males than E2-treated males.