Estrogens, produced by ovaries and testis, affect growth and differentiation of many target tissues. These include the male and female reproductive tissues (mammary gland, uterus, ovary, and prostate). Estrogens have also been implicated in the physiology of the bone, cardiovascular tissues, and the brain. Estrogens bind to the intracellular proteins known as estrogen receptors (ER). Estrogen receptor is a member of the super family of nuclear receptor that show a similar structure and mode of action. Once bound by their ligand, ER undergoes a conformational change to a form that can specifically binds to its target genes and later their transcription. Structurally, nuclear receptors have been divided into six distinct domains termed A-F: The hypervariable N-terminal transactivation domain, the DNA-binding, dimerization, and nuclear localization conserved region C, and the ligand binding conserved region E. A great deal of knowledge has been obtained from the cloning, structure and functional studies of previously known ER (now called ERa).

The ERa, initially cloned from uterus, is highly homologous to the ERa from mouse, human, and chicken. Recently, another form of the ER, termed ERb1, has been cloned from rat and human tissue. Rat/mouse ERb1 gene encodes a protein of 485 aa with a calculated size of approx. 54 kDa. ERb1 is 477 aa in human. As compared to ERa, ERb1 is highly conserved in the DNA-binding domain (>90% homology) and the C-terminal ligand binding domain (55% homology). The A/B domain, the hinge region and the F-domain are not conserved. Rat ERb1 is primarily expressed in prostate, ovary, lung, bladder, brain, uterus, and testis. ligand binding experiments with the recombinant ERb1 revealed a single binding component for 17b-E2 with Kd=0.6 nM. Both ERa and ERb1 bins to common agonists and antagonists with more or less overlapping specificity.

Most recently functional variants of ERb1, termed ERb2, have been cloned. ERb2 has an additional 18 aa as a results of in-frame mutation within the ligand-binding domain. ERb2 is expressed in ovary, prostate, pituitary, brain, and muscle. Variants of both ERb1 and ERb2 (ERb1d3, ERb2d3) were detected that show deletion of 39 aa in the DNA-binding domain. Both ERb1 and ERb2 specifically bind to ER response element. ERa, b1 and ERb2 have been found to heterodimerize with each other.

The physiological significance of the presence of two multiple ER subtypes are not clearly understood. Recently, an examination of transactivation properties of the two ER isoforms revealed that ERa and ERb signal in opposite ways when bound to estradiol.. The ERa activates certain genes while in combination with ERb it has no effect. Several anti-estrogens were found to be potent transcriptional activators with ERb at an AP1 site. It would thus appear that ERa and ERb may play different roles in gene regulation.

ADI has produced highly specific rabbit-anti rat and human ERb1, and ERb2 using specific peptide sequences. The selected peptides have no appreciable homology with the ERa. Availability of multiple antibodies to the same protein should help select antibodies with more interspecies crossreactivity, and to achieve better results in a given technique. The control immunogenic peptides are also available to confirm specificity of antibodies. Mouse monoclonal Anti-ERa is also available for control and comparative studies. This antibody is suitable for Western, immunohistochemistry, etc.

M= Mouse; R=Rat; H=Human; Rb=Rabbit; B=Bovine; CT= near C-terminus; NT=near N-terminus; Internal=Middle of protein.

Control peptides, because of thier small sizes (1-3K) are not suitable for Western. They are intended for ELISA or antibody competition studies. These are provided as "free" or unconjugated forms.
Neat Antiserum represents crude, undiluted, and non-purified serum. It is is OK for studies in Western or ELISA.
Affinity pure antibodies (purified over the antigen/peptide columns), in general, will give cleaner background and recommended for IHC or IP applications.