Browsing by Subject "Estrogen--Receptors"

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Characterization of a nuclear estrogen receptor in the testis of Atlantic croaker (Micropogonias undulatus) and effects of estrogen on testicular steroidogenesis
(1998) Loomis, Anna Katrina; Thomas, P. (Peter)
An estrogen receptor (ER) was identified in the nuclear and cytosolic fractions of the testis in the marine teleost, Atlantic croaker (Micropogonias undulatus). Competition studies demonstrated that the receptor was highly specific for estrogens and that a variety of xenoestrogens bound to the receptor with relatively low binding affinities. A comparison of the binding affinities of ligands for the testicular and hepatic ERs in this species revealed that the testicular ER saturated at a lower estradiol concentration and also had higher binding affinities for most of the estrogens and xenoestrogens tested. Minor amounts of estradiol were produced by testicular tissue fragments incubated in vitro. Incubation of testicular fragments in vitro with estradiol caused a concentration-dependent decrease in gonadotropin-stimulated 11-ketotestosterone (11-KT) production. Estradiol is acting on the cell surface via a non-genomic mechanism to alter 11-KT production
The identification and characterization of three distinct estrogen receptor subtypes in a teleost fish, the Atlantic croaker (Micropogonias undulatus)
(2002) Hawkins, Mary Beth; Thomas, P. (Peter)
This dissertation identifies and characterizes three distinct estrogen receptors in a teleost fish, the Atlantic croaker, Micropogonias undulatus. Atlantic croaker possess ERα, ERβ, and a previously unrecognized form we call ERγ. This is the first description of three ER subtypes in any vertebrate. Phylogenetic analysis shows that ERγ arose via gene duplication from ERβ early in the teleost lineage, and indicates that ERγ is present in other teleosts, but has not been recognized. The three ER subtypes are genetically distinct and have different distribution patterns in Atlantic croaker tissues. The Atlantic croaker (ac)ERγ shows amino acid differences in regions important for ligand-binding and receptor activation that are conserved in all other ERγs. Bacterially expressed fusion proteins for acERα, β, and γ show specific, high affinity binding to [3 H] estradiol (E2) with Kds of 0.61± 0.013, 0.40 ± 0.006, and 0.38 ± 0.059 nM respectively. The rank orders of binding to the acER fusion proteins are DES >> ICI182 > TOH > ICI164 > E2 ≥ ZEAR > MOX E >TAM > E1 ≥ 17αE2 > E3 > 2OH E = GEN >> RU 486 for acERα; ICI182 > DES > TOH > E2 > ICI164 > GEN > MOX E > TAM > ZEAR = E1 > E3 = 17αE2 > 2OH E >> RU 486 for acERβ; and E2 ≥ DES > TOH > ICI182 > ICI164 > E3 ≥ GEN > MOX E > ZEAR > E1 > 17αE2 > RU 486 ≥ TAM > 2OH E for acERγ. The acER subtypes are expressed in expected areas of the forebrain, but their distributions within these regions differ. acERα is found in all brain regions previously demonstrated to concentrate E2 or possess ERs. acERγ, but not acERβ, is detected in the nucleus suprachiasmaticus and dorsal preopticus parvocellularis anterior (PPa). Conversely, acERβ, but not acERγ was found in the ventral PPa, preopticus magnocellularis pars magnocellularis, and cerebellar Purkinje cells. The presence of three functional ERs in one species expands the role of estrogen receptor multiplicity in estrogen signaling systems and clarifies the dynamics and mechanisms of estrogen receptor evolution.