Identification and Characterization of Estrogen and Progesterone Receptors from the Oviduct of the American Alligator (Alligator mississippiensis)

Abstract

A protein extract prepared from the egg shell fiber-secreting region of the oviduct ofAlligator mississippiensiswas assayed for the presence of receptors for estrogen and progesterone. In the presence of [3H]estradiol-17β, the extract contained an estrogen-binding activity which reached equilibrium at 25 °C in 1 h. Scatchard analysis demonstrated that a single estrogen-binding activity was present in the extract with a Kd of 0.5 nM for [3H]estradiol-17β. A steroid specificity competition assay showed the estrogen binding activity strongly recognized estradiol-17β and diethylstilbestrol (DES) and weakly interacted with estrone, estriol, estradiol-17α, and dihydrotestosterone (DHT). The estrogen binding activity did not recognize testosterone, dexamethasone or progesterone. The extract exhibited a DNA-binding activity that recognized an estrogen response element in a gel mobility shift assay. We have also identified a high affinity binding activity in the extract that specifically recognized the synthetic progestin R5020 with a Kd of 0.9 nM. This binding activity recognized 17α-estradiol, dexamethasone, testosterone, and estriol. This activity did not recognize DHT, DES, or estradiol-17β. These data suggest the presence of estrogen and progesterone receptors in the oviduct of the alligator.