Vitellogenin as a biomarker of exposure for estrogen or estrogen mimics

Vitellogenin, the egg yolk precursor protein, has become a popular biomarker for measuring exposure of oviparous animals to estrogen or estrogen mimics. Vitellogenin is normally produced by females in response to normal cycles of estradiol during oogenesis. The gene for vitellogenin is also present in the livers of males but it is normally silent. Upon exposure to estrogen or to an estrogen mimic, the gene is turned on and vitellogenin is synthesized. After synthesis, it is exported into the blood where, in males, it remains until it is degraded or cleared out by the kidneys. In females, vitellogenin is taken up by the developing oocyte through receptor mediated endocytosis. There are several assays in the literature for measuring vitellogenin levels in plasma. The easiest method is through antibody based assays including ELISA (enzyme-linked immunosorbent assay) or by western blot. Competition or sandwich ELISAs are the most sensitive assays and they can detect vitellogenin in plasma in the nanogram to milligram per ml range. This chapter discusses methods for purifying vitellogenin from plasma, generating antibodies, and performing assays to measure vitellogenin.