CHARACTERIZATION OF ESTROGEN BINDING IN THE DEVELOPING RAT TESTIS ONTOGENY OF THE TESTICULAR CYTOPLASMIC ESTROGEN-RECEPTOR

The properties and physical characteristics of a steroid binding component present in the immature (7 to 35 day) rat were investigated and found to be different from those of the 17β-estradiol receptor in the mature rat testis. These properties include a binding capacity of 483 fmol estradiol/mg protein, a Ka at equilibrium of 4.23 × 107M-1, and broad steroid specificity as shown by interaction with several steroids; no binding was observed with diethylstilbestrol. The component, found in blood and several tissues including the testis, migrated as a 4.6S peak on sucrose gradients. This 4.6S component, which interacted with an anti-alphafetoprotein antiserum, decreased with age and was not detectable in the testis after day 21 or in the serum after day 25. These data suggest that this component is alphafetoprotein. Ontogenic appearance of the testicular cytoplasmic 17β-estradio receptor in the developing rat was further elucidated. Sucrose gradient sedimentation analysis of cytosols revealed an 8S binding component that was first detectable at 23 days. Specific binding (fmol [3H]-estradiol/testis) was relatively low in neonates, rose to 59 fmol during the third week, and increased dramatically to 333 fmol at 7 weeks; binding rose only gradually after maturity. The receptor was tissue specific and steroid specificity studies demonstrated that only diethylstilbestrol and other estrogens were effective in competing with 17β-estradio1 for binding sites. The Ka at equilibrium was determined as 3 × 1010M-1 and the binding sites were saturable in an in vitro system. The receptor did not interact with anti-alphafetoprotein antiserum as indicated by sucrose gradient studies. These data demonstrate the developmental appearance of the testicular cytoplasmic estradiol receptor in the immature rat. © 1979.