All scientific investigations begin with distinct objectives: first is the hypothesis upon which studies are undertaken to disprove, and second is the overall aim of obtaining further information, from which future and more precise hypotheses may be drawn Studies focusing on the generation and use of gene-targeted animal models also apply these goals and may be loosely categorized into sequential phases that become apparent as the use of the model progresses Initial studies of knockout models often focus on the plausibility of the model based on prior knowledge and whether the generation of an animal lacking the particular gene will prove lethal or not Upon the successful generation of a knockout, confirmatory studies are undertaken to corroborate previously established hypotheses of the function of the disrupted gene product As these studies continue, observations of unpredicted phenotypes or, more likely, the lack of a phenotype that was expected based on models put forth from past investigations are noted Often the surprising phenotype is due to the loss of a gene product that is downstream from the functions of the disrupted gene, whereas the lack of an expected phenotype may be due to compensatory roles filled by alternate mechanisms As the descriptive studies of the knockout continue, use of the model is often shifted to the role as a unique research reagent, to be used in studies that 1) were not previously possible in a wild-type model; 2) aimed at finding related proteins or pathways whose existence or functions were previously masked; or 3) the subsequent effects of the gene disruption on related physiological and biochemical systems The alpha ERKO mice continue to satisfy the confirmatory role of a knockout quite well As summarized in Table 4, the phenotypes observed in the alpha ERKO due to estrogen insensitivity have definitively illustrated several roles that were previously believed to be dependent on functional ER alpha, including 1) the proliferative and differentiative actions critical to the function of the adult female reproductive tract and mammary gland; 2) as an obligatory component in growth factor signaling in the uterus and mammary gland; 3) as the principal steroid involved in negative regulation of gonadotropin gene transcription and LH levels in the hypothalamic-pituitary axis; 4) as a positive regulator of PR expression in several tissues; 5) in the positive regulation of PRL synthesis and secretion from the pituitary; 6) as a promotional factor in oncogene-induced mammary neoplasia; and 7) as a crucial component in the differentiation and activation of several behaviors in both the female and male The list of unpredictable phenotypes in the alpha ERKO must begin with the observation that generation of an animal lacking a functional ER alpha gene was successful and produced animals of both sexes that exhibit a life span comparable to wild-type The successful generation of beta ERKO mice suggests that this receptor is also not essential to survival and was most likely not a compensatory factor in the survival of the alpha ERKO In support of this is our recent successful generation of double knockout, or alpha beta ERKO mice of both sexes The precise defects in certain components of male reproduction, including the production of abnormal sperm and the loss of intromission and ejaculatory responses that were observed in the alpha ERKO, were quite surprising In turn, certain estrogen pathways in the alpha ERKO female appear intact or unaffected, such as the ability of the uterus to successfully exhibit a progesterone-induced decidualization response, and the possible maintenance of an LH surge system in the hypothalamus [ABSTRACT TRUNCATED]

Estrogen receptor null mice: what have we learned and where will they lead us?

https://digital.csic.es/bitstream/10261/72251/1/GarciaSegura%2c2001%2cProgressNeurobiol.%2c63%2c29-.pdf

Neuroprotection by estradiol.

Estrogen receptor α (ERα) and ERβ are members of the steroid nuclear receptor family that modulate gene transcription in an estrogen-dependent manner. ER mRNA and protein have been detected both peripherally and in the central nervous system, with most data having come from the rat. Here we report the development of an ERβ-selective antibody that cross-reacts with mouse, rat, and human ERβ protein and its use to determine the distribution of ERβ in the murine brain. Further, a previously characterized polyclonal antibody to ERα was used to compare the distribution of the two receptors in the first comprehensive description of ER distribution specifically in the mouse brain. ERβ immunoreactivity (ir) was primarily localized to cell nuclei within select regions of the brain, including the olfactory bulb, cerebral cortex, septum, preoptic area, bed nucleus of the stria terminalis, amygdala, paraventricular hypothalamic nucleus, thalamus, ventral tegmental area, substantia nigra, dorsal raphe, locus coeruleus...

/pdf/immunolocalization-of-estrogen-receptor-b-in-the-mouse-brain-118u5ulh1h.pdf

Immunolocalization of estrogen receptor β in the mouse brain: Comparison with estrogen receptor α

Oestrogens exert their actions via specific nuclear protein receptors that are members of the steroid/thyroid receptor superfamily of transcription factors. Recently, a second oestrogen receptor (ERbeta) has been cloned, and using reverse transcription-PCR and immunohistochemistry it has been shown to have a wide tissue distribution in the rat that is distinct from the classical oestrogen receptor, ERalpha. Using commercial polyclonal antisera against peptides specific to human ERbeta, we have determined the sites of ERbeta expression in archival and formalin-fixed human tissue and compared its expression with that of ERalpha. ERbeta was localised to the cell nuclei of a wide range of normal adult human tissues including ovary, Fallopian tube, uterus, lung, kidney, brain, heart, prostate and testis. In the ovary, ERbeta was present in multiple cell types including granulosa cells in small, medium and large follicles, theca and corpora lutea, whereas ERalpha was weakly expressed in the nuclei of granulosa cells, but not in the theca nor in the copora lutea. In the endometrium, both ERalpha and ERbeta were observed in luminal epithelial cells and in the nuclei of stromal cells but, significantly, ERbeta was weak or absent from endometrial glandular epithelia. Epithelial cells in most male tissues including the prostate, the urothelium and muscle layers of the bladder, and Sertoli cells in the testis, were also immunopositive for ERbeta. Significant ERbeta immunoreactivity was detected in most areas of the brain, with the exception of the hippocampus - a tissue that stained positively for ERalpha. In conclusion, the almost ubiquitous immunohistochemical localisation of ERbeta indicates that ERbeta may play a major role in the mediation of oestrogen action. The differential expression of ERalpha and ERbeta in some of these tissues suggests a more complex control mechanism in oestrogenic potential than originally envisioned.

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Immunolocalisation of oestrogen receptor beta in human tissues

The discovery of estrogen receptor β (ERβ) and subsequent localization of its mRNA in the rat central nervous system (CNS) has provided new insights about estrogen action in brain A critical step in understanding the role of ERβ is demonstrating that the mRNA is translated into functional protein The present study used a new ERβ-specific polyclonal antiserum (Z8P) and immunocytochemistry (ICC) to investigate the distribution of ERβ in the rat CNS Ovariectomized female rats were perfusion fixed, and free-floating sections were incubated with Z8P After visualization with a standard ABC method, nuclear immunoreactivity was seen in neurons throughout the brain, including the olfactory nuclei, laminae IV–VI of the cerebral cortex, medial septum, preoptic area, bed nucleus of the stria terminalis, supraoptic nucleus, paraventricular nucleus, zona incerta, medial and cortical amygdaloid nuclei, cerebellum, nucleus of the solitary tract, ventral tegmental area, and spinal trigeminal nucleus Moreover, the results of a double-label ICC/ in situ hybridization study revealed that ERβ mRNA and immunoreactivity were colocalized in neurons of the brain, thus confirming the specificity of the antiserum Through the use of Western blot analysis, Z8P was shown to recognize in vitro translated ERβ, but not ERα, as well as a 60-kDa protein from rat granulosa cells and ovary extracts The results of these studies have demonstrated that (1) ERβ mRNA is translated into immunoreactive protein throughout the rat brain, and (2) ERβ resides in the cell nucleus Together, these data provide an anatomic foundation for future studies and advance our understanding of estrogen action in hypothalamic and extrahypothalamic brain regions J Comp Neurol 436:64–81, 2001 © 2001 Wiley-Liss, Inc

Distribution of estrogen receptor β immunoreactivity in the rat central nervous system

Neurons in the hypothalamus of estrogen receptor alpha-knockout (ER alphaKO) mice have been shown to concentrate radiolabeled estrogen and estrogen treatment regulates the expression of progesterone receptor mRNA The purpose of the present study was to utilize in situ hybridization histochemistry to determine the anatomical distribution of ER beta mRNA in ER alphaKO mouse forebrain The results of these studies revealed an extensive distribution of ER beta mRNA in the hypothalamic regions including medial preoptic area, suprachiasmatic nucleus, paraventricular nucleus, dorsomedial nucleus, medial tuberal nucleus, and the premammillary nuclei Additional labeled perikarya were also detected in the glomerular layer of the olfactory bulb; tenia tecta; anterior septum; bed nucleus of the stria terminalis; medial, basolateral and cortical nuclei of the amygdala; cerebral and entorhinal cortex; the septohippocampal nucleus; Ammon's horn of the hippocampus and the dorsal raphe The results of these in situ hybridization histochemical studies have provided novel information about the distribution of ER beta mRNA in the ER alphaKO mouse forebrain In addition, these morphological data provides evidence that estrogen may exert its actions in the ER alphaKO mouse brain via ER beta and thereby maintain organizational and activational effects

/pdf/the-distribution-of-estrogen-receptor-beta-mrna-in-forebrain-2hoer0vj4b.pdf

Roger Askew

Papers

The distribution of estrogen receptor-beta mrna in forebrain regions of the estrogen receptor-alpha knockout mouse