The role of estrogen receptor-α and its activation function-1 for growth plate closure in female mice

High estradiol levels in late puberty induce growth plate closure and thereby cessation of growth in humans. In mice, the growth plates do not fuse after sexual maturation, but old mice display reduced longitudinal bone growth and high-dose estradiol treatment induces growth plate closure. Estrogen receptor (ER)-α stimulates gene transcription via two activation functions (AFs), AF-1 and AF-2. To evaluate the role of ERα and its AF-1 for age-dependent reduction in longitudinal bone growth and growth plate closure, female mice with inactivation of ERα (ERα(-/-)) or ERαAF-1 (ERαAF-1(0)) were evaluated. Old (16- to 19-mo-old) female ERα(-/-) mice showed continued substantial longitudinal bone growth, resulting in longer bones (tibia: +8.3%, P < 0.01) associated with increased growth plate height (+18%, P < 0.05) compared with wild-type (WT) mice. In contrast, the longitudinal bone growth ceased in old ERαAF-1(0) mice (tibia: -4.9%, P < 0.01). Importantly, the proximal tibial growth plates were closed in all old ERαAF-1(0) mice while they were open in all WT mice. Growth plate closure was associated with a significantly altered balance between chondrocyte proliferation and apoptosis in the growth plate. In conclusion, old female ERα(-/-) mice display a prolonged and enhanced longitudinal bone growth associated with increased growth plate height, resembling the growth phenotype of patients with inactivating mutations in ERα or aromatase. In contrast, ERαAF-1 deletion results in a hyperactive ERα, altering the chondrocyte proliferation/apoptosis balance, leading to growth plate closure. This suggests that growth plate closure is induced by functions of ERα that do not require AF-1 and that ERαAF-1 opposes growth plate closure.

The estrogen-responsive adrenomedullin and receptor-modifying protein 3 gene identified by DNA microarray analysis are directly regulated by estrogen receptor

Recent studies have revealed that hundreds of genes in the uterus are activated by estrogen. Their expression profiles differ over time and doses and it is not clear whether all these genes are directly regulated by estrogen via the estrogen receptor. To select the genes that may be regulated by estrogen, we treated mice with several doses of estrogen and searched for those genes whose dose-response expression pattern mirrored the uterine growth pattern. Among those genes, we found that the dose-dependent expression of the adrenomedullin (ADM) gene correlated well with the uterotrophic effect of estrogen. ADM expression is induced early after estrogen administration and is restricted to the endometrial stroma. The spatiotemporal gene expression pattern of ADM was similar to that of receptor-modifying protein 3 (RAMP3). RAMP3 is known to modify calcitonin gene-related receptor (CRLR) so that it can then serve as an ADM receptor. Chromatin immunoprecipitation assays indicated that the estrogen receptor binds directly to the ADM promoter region and RAMP3 intron after estrogen administration. It was also shown that neither the ADM nor RAMP3 gene could be activated in estrogen receptor-alpha-null mouse. Although uterine ADM expression has been reported to occur in the myometrium, our observations indicate that estrogen-induced ADM is also expressed in the uterine stroma and that such variable, spatiotemporally regulated ADM expression contributes to a wider range of biological effects than previously expected.

Role of foxj1 and estrogen receptor alpha in ciliated epithelial cell differentiation of the neonatal oviduct

Estrogen regulates proliferation and differentiation of epithelial cells in the mammalian oviduct, but pathways for cell-specific differentiation are not well understood. In the epithelial cells of the developing rat oviduct, we found estrogen receptor (ER) alpha is expressed at birth and persists in all cells through neonatal day (ND) 7 when ciliated cells appear. To determine a specific function of ER and foxj1, a transcription factor known to have fundamental roles in ciliogenesis in the lung, in differentiation of the ciliated epithelial cells, we treated newborn rats from ND 0 to 5 with estradiol-17beta (E2) with and without a selective ER antagonist. E2 enhanced the number of proliferating cells and accelerated the process of epithelial cell differentiation resulting in ciliogenesis by ND 5, and co-treatment with an ER antagonist inhibited these changes. Foxj1 was expressed only in the infundibulum and ampulla (INF/AMP). That expression preceded the appearance of cilia and was induced by E2. Cilia were absent in oviducts of foxj1-deficient mice, indicating that foxj1 plays a critical role in oviductal ciliogenesis. However, we found the presence of cilia in the ERalpha-deficient mouse oviduct. The widespread expression of ERalpha in oviductal epithelium, but restriction of cilia to the INF/AMP regions, and importantly, the presence of cilia in the ERalpha-deficient mice, suggested ER signaling is not essential for ciliated epithelial cell differentiation. These observations demonstrate that, although E2 stimulates the differentiation process of ciliated epithelial cells, foxj1 is directly required for epithelial cell ciliogenesis of the neonatal oviduct.

Role of Fibroblast Growth Factor-2 Isoforms in the Effect of Estradiol on Endothelial Cell Migration and Proliferation

Both 17beta-estradiol (E2) and fibroblast growth factor-2 (FGF2) stimulate angiogenesis and endothelial cell migration and proliferation. The first goal of this study was to explore the potential link between this hormone and this growth factor. E2-stimulated angiogenesis in SC Matrigel plugs in Fgf2+/+ mice, but not in Fgf2-/- mice. Cell cultures from subcutaneous Matrigel plugs demonstrated that E2 increased both migration and proliferation in endothelial cells from Fgf2+/+ mice, but not from in Fgf2-/- mice. Several isoforms of fibroblast growth factor-2 (FGF2) are expressed: the low molecular weight 18-kDa protein (FGF2lmw) is secreted and activates tyrosine kinase receptors (FGFRs), whereas the high molecular weight (21 and 22 kDa) isoforms (FGF2hmw) remains intranuclear, but their role is mainly unknown. The second goal of this study was to explore the respective roles of FGF2 isoforms in the effects of E2. We thus generated mice deficient only in the FGF2lmw (Fgf2lmw-/-). E2 stimulated in vivo angiogenesis and in vitro migration in endothelial cells from Fgf2lmw-/- as it did in Fgf2+/+ mice. E2 increased FGF2hmw protein abundance in endothelial cell cultures from Fgf2+/+ and Fgf2lmw-/- mice. As shown using siRNA transfection, these effects were FGFR independent but involved FGF2-Interacting Factor, an intracellular FGF2hmw partner. This is the first report for a physiological role for the intracellular FGF2hmw found to mediate the effect of E2 on endothelial cell migration via an intracrine action.

Estradiol alters nitric oxide production in the mouse aorta through the alpha-, but not beta-, estrogen receptor

Although estradiol (E(2)) has been recognized to exert several vasculoprotective effects in several species, its effects in mouse vasomotion are unknown, and consequently, so is the estrogen receptor subtype mediating these effects. We investigated the effect of E(2) (80 microg/kg/day for 15 days) on NO production in the thoracic aorta of ovariectomized C57Bl/6 mice compared with those given placebo. E(2) increased basal NO production. In contrast, the relaxation in response to ATP, to the calcium ionophore A23187, and to sodium nitroprusside was unaltered by E(2), whereas acetylcholine-elicited relaxation was decreased. The abundance of NO synthase I, II, and III immunoreactive proteins (using Western blot) in thoracic aorta homogenates was unchanged by E(2). To determine the estrogen receptor (ER) subtype involved in these effects, transgenic mice in which either the ERalpha or ERbeta has been disrupted were ovariectomized and treated, or not, with E(2). Basal NO production was increased and the sensitivity to acetylcholine decreased in ERbeta knockout mice in response to E(2), whereas this effect was abolished in ERalpha knockout mice. Finally, these effects of E(2) on vasomotion required long-term and/or in vivo exposure, as short-term incubation of aortic rings with 10 nmol/L E(2) in the isolated organ chamber did not elicit any vasoactive effects. In conclusion, this study demonstrates that ERalpha, but not ERbeta, mediates the beneficial effect of E(2) on basal NO production.

The AF-1 activation-function of ERalpha may be dispensable to mediate the effect of estradiol on endothelial NO production in mice

Two isoforms of estrogen receptor (ER) have been described: ERalpha and ERbeta. The initial gene targeting of ERalpha, consisting in the introduction of a Neo cassette in exon 1 [alphaERKO, hereafter called ERalpha-Neo KO (knockout)], was reported in 1993. More recently, another mouse deficient in ERalpha because of the deletion of exon 2 (ERalphaKO, hereafter called ERalpha-delta2 KO) was generated. In ovariectomized ERalpha-wild-type mice, estradiol (E(2)) increases uterine weight and basal production of endothelial nitric oxide (NO). Both of these effects are abolished in ERalpha-delta2 KO mice. In contrast, we show here that both of these effects of E(2) are partially (uterine weight) or totally (endothelial NO production) preserved in ERalpha-Neo KO. We also confirm the presence of two ERalpha mRNA splice variants in uterus and aorta from ERalpha-Neo KO mice. One of them encodes a chimeric ERalpha protein (ERalpha55), partially deleted in the A/B domain, that was detected in both uterus and aorta by Western blot analysis. The other ERalpha mRNA splice variant codes for an isoform deleted for the A/B domain (ERalpha46), which was detected in uterus of ERalpha-Neo KO, and wild-type mice. This protein isoform was not detected in aorta. The identification of these two N-terminal modified isoforms in uterus, and at least one of them in aorta, probably explains the persistence of the E(2) effects in ERalpha-Neo KO mice. Furthermore, ERalpha-Neo KO mice may help in the elucidation of the specific functions of full-length ERalpha (ERalpha66) and ERalpha46, both shown to be physiologically generated in vivo.

Deletion of estrogen receptors reveals a regulatory role for estrogen receptors-beta in bone remodeling in females but not in males

To determine the contributions of estrogen receptor (ER)alpha and ERbeta in bone growth and remodeling in male and female mice, we generated and analyzed full knockouts for each receptor, and a double ER knockout. Although suppression of the ligand to the ERs (i.e., estradiol) after menopause or gonadectomy in females led to a catastrophic increase in bone turnover and concomitant bone loss, deletion of one or both ERs failed to show such an effect. Complete deletion of ERalpha led to a decrease, not an increase, in bone turnover and an increase, not a decrease, in trabecular bone volume in both male and female animals. Deletion of ERbeta led to different responses in males, where bone was unaffected, and in females, where bone resorption was decreased and trabecular bone volume increased. In contrast, deletion of both ERs led to a profound decrease in trabecular bone volume in females, which was associated with a decrease, not an increase, in bone turnover. Finally, deletion of ERalpha, but not ERbeta, led to major changes in circulating levels of estradiol and/or testosterone, indirectly affecting bone remodeling and bone mass. Thus, only ERalpha was shown to regulate bone remodeling in males, whereas in females both receptor subtypes influenced this process and could, at least under basal knockout conditions, compensate for each other.

Increased anxiety and synaptic plasticity in estrogen receptor beta -deficient mice

Estrogens are powerful modulators of neuronal physiology and in humans may affect a broad range of functions, including reproductive, emotional, and cognitive behaviors. We studied the contribution of estrogen receptors (ERs) in modulation of emotional processes and analyzed the effects of deleting ERalpha or ERbeta in mice. Behavior consistent with increased anxiety was observed principally in ERbeta mutant females and was associated with a reduced threshold for the induction of synaptic plasticity in the basolateral amygdala. Local increase of 5-hydroxytryptamine 1a receptor expression in medial amygdala may contribute to these changes. Our data show that, particularly in females, there is an important role for ERbeta-mediated estrogen signaling in the processing of emotional behavior.

Estradiol accelerates reendothelialization in mouse carotid artery through estrogen receptor-alpha but not estrogen receptor-beta

BACKGROUND

The atheroprotective effect of 17beta-estradiol (E(2)) has been suggested in women and clearly demonstrated in animals through both an effect on lipid metabolism and a direct effect on the cells of the arterial wall. It has been shown, for example, that E(2) promotes endothelium-dependent relaxation and accelerates reendothelialization in rats. Similar studies have been undertaken in mice to appreciate the molecular mechanism of this process.

METHODS AND RESULTS

We report here a model of electric carotid injury adapted from that described by Carmeliet et al (1997) that allows us to precisely evaluate the reendothelialization process. We demonstrate that E(2) accelerates endothelial regeneration in castrated female wild-type mice. In ovariectomized transgenic mice in which either the estrogen receptor (ER)-alpha or ERbeta gene has been disrupted, E(2) accelerated reendothelialization in female ERbeta knockout mice, whereas this effect was abolished in female ERalpha knockout mice.

CONCLUSIONS

This study demonstrates that ERalpha but not ERbeta mediates the beneficial effect of E(2) on reendothelialization and potentially the prevention of atherosclerosis.

Effect of single and compound knockouts of estrogen receptors alpha (ERalpha) and beta (ERbeta) on mouse reproductive phenotypes

The functions of estrogen receptors (ERs) in mouse ovary and genital tracts were investigated by generating null mutants for ERalpha (ERalphaKO), ERbeta (ERbetaKO) and both ERs (ERalphabetaKO). All ERalphaKO females are sterile, whereas ERbetaKO females are either infertile or exhibit variable degrees of subfertility. Mast cells present in adult ERalphaKO and ERalphabetaKO ovaries could participate in the generation of hemorrhagic cysts. Folliculogenesis proceeds normally up to the large antral stage in both ERalphaKO and ERbetaKO adults, whereas large antral follicles of ERalpha+/−ERbetaKO and ERalphabetaKO adults are markedly deficient in granulosa cells. Similarly, prematurely developed follicles found in prepubertal ERalphaKO ovaries appear normal, but their ERalphabetaKO counterparts display only few granulosa cell layers. Upon superovulation treatment, all prepubertal ERalphaKO females form numerous preovulatory follicles of which the vast majority do not ovulate. The same treatment fails to elicit the formation of preovulatory follicles in half of the ERbetaKO mice and in all ERalpha+/−/ERbetaKO mice. These and other results reveal a functional redundancy between ERalpha and ERbeta for ovarian folliculogenesis, and strongly suggest that (1) ERbeta plays an important role in mediating the stimulatory effects of estrogens on granulosa cell proliferation, (2) ERalpha is not required for follicle growth under wild type conditions, while it is indispensable for ovulation, and (3) ERalpha is also necessary for interstitial glandular cell development. Our data also indicate that ERbeta exerts some function in ERalphaKO uterus and vagina. ERalphabetaKO granulosa cells localized within degenerating follicles transform into cells displaying junctions that are unique to testicular Sertoli cells. From the distribution pattern of anti-Mullerian hormone (AMH) in ERalphabetaKO ovaries, it is unlikely that an elevated AMH level is the cause of Sertoli cell differentiation. Our results also show that cell proliferation in the prostate and urinary bladder of old ERbetaKO and ERalphabetaKO males is apparently normal.

Retinoic acid receptor beta 2 (RAR beta 2) null mutant mice appear normal

Vertebrates are highly sensitive to both retinoic acid (RA) deficiency and excess. The RA signal is thought to be transduced by nuclear receptors (the RAR and RXR families) which activate the expression of target genes via cis-acting transcriptional enhancer elements. Each of the three RAR genes, RAR alpha, RAR beta, and RAR gamma, gives rise to several isoforms by differential usage of two promoters and alternative splicing. RAR beta 2 is the most abundant of the four RAR beta isoforms, and its transcription is spatially and temporally restricted in developing embryos, suggesting that it might perform specific functions. Furthermore, RAR beta 2 expression can be induced via a retinoic acid response element located in its promoter region. This RA effect is particularly interesting since under conditions of RA excess, RAR beta 2 promoter activity and transcript accumulation are induced in regions of developing embryos in which malformations subsequently appear, such as the craniofacial region, the hindbrain, and the limbs. These findings have led to the suggestion that the RAR beta 2 isoform might mediate some of the teratogenic effects of RA. In this study, we have eliminated RAR beta 2 expression by targeted gene disruption. RAR beta 2 null mutants exhibit an apparently normal phenotype, indicating that other RARs must compensate for RAR beta 2 sufficiently well to allow normal prenatal and postnatal development to proceed. By challenging RAR beta 2 null embryos with teratogenic doses of RA, we have also directly addressed the question of whether RAR beta 2 is required for mediating RA-induced malformations.

Retinoic acid signal transduction pathways

Complexity in the retinoid signaling system arises from a combination of several forms of retinoic acid which possess differential activities, multiple cytoplasmic binding proteins and nuclear receptors that have distinct ligand specificities and functional properties, and the existence of polymorphic retinoic acid response elements. Additional diversity appears to be generated by heterodimeric interactions between the two classes of nuclear retinoic acid receptors and between retinoic acid receptors and some other members of the nuclear receptor superfamily. Thus, a complex array of combinatorial effects is beginning to emerge that may account for the pleiotropic effects of retinoids.

Retinoic acid receptors and binding proteins in human skin

Nuclear retinoic acid receptors (RAR) are likely to mediate many of the pleiotypic cutaneous actions of retinoids by acting as ligand-dependent enhancer factors. The presence of nuclear RAR in skin was confirmed by identification of a 45-kDa nuclear RA binding activity by fast protein liquid chromatography (FPLC). Analysis of RNA extracted from skin specimens demonstrated expression of RAR-alpha and RAR-gamma transcripts, as well as expression of the homologous low-affinity receptor, RXR-alpha. Both isoforms of RAR-gamma RAR-gamma 1 and RAR-gamma 2 were detectable, with RAR-gamma 1 being the more strongly expressed. FPLC analysis also demonstrated a 15-kDa peak of specific RA binding activity, consistent with the presence of cellular retinoic acid binding protein (CRABP). Of the two known forms of CRABP, CRABP-II was much more strongly expressed than CRABP-I at the level of steady-state mRNA. CRABP-II was also expressed in keratinocytes and fibroblasts in vitro. CRABP-II was up-regulated by agents that induce keratinocyte differentiation, and inhibited by prolonged exposure to high concentrations of RA. In contrast, CRABP-II was consistently induced by RA in dermal, but not in lung fibroblasts. CRABP-I was expressed at low to undetectable levels under all these conditions. The presence of tissue-specific and differentiation-related regulation of CRABP-II suggests that it may be an important regulator of RA action in human skin.

Retinoic acid receptors as regulators of human epidermal keratinocyte differentiation

To examine the role of nuclear retinoic acid (RA) receptors (RARs) in the regulation of squamous differentiation in normal human epidermal keratinocytes (NHEK), we analyzed binding activity, mRNA expression, and transcriptional activity of the endogenously expressed RARs. Specific RA-binding activity eluted from size-exclusion HPLC with an apparent mol wt of 50 kilodaltons and was predominantly (greater than 95%) associated with the NHEK nuclear cell fraction. This RAR-binding activity represented in part the expression of RAR alpha and RAR gamma genes, whose transcripts were expressed in similar abundance in undifferentiated NHEK. Differentiation resulted in lower mRNA expression of RAR alpha relative to the mRNA expression of RAR gamma. Treatment of NHEK cells with 10(-6) M RA did not induce expression of RAR beta mRNA. Similarly, three squamous cell carcinoma cell lines derived from human skin and oral cavity expressed RAR alpha and RAR gamma transcripts, but not RAR beta transcripts. Transfection of NHEK with chloramphenicol acetyltransferase (CAT) reporter plasmids indicated that the endogenously expressed RARs could activate transcription through the RAR beta response element in a concentration-dependent manner with doses of 10(-9) M RA and higher. CAT expression was not activated through TRE, a palindromic thyroid hormone response element with purported RA responsiveness. The competitive binding of benzoic acid derivatives of RA to RAR correlated with the ability of each analog to suppress mRNA expression of the squamous cell markers, involucrin, type I transglutaminase, and SQ37, and to activate transcription of the RAR beta response element-CAT reporter. These results demonstrate that the control of NHEK differentiation by RA is consistent with the interaction of the retinoid with RAR and the regulation of transcription by that ligand-receptor complex.

Differential regulation of retinoic acid receptors and binding proteins in human skin

Many of the pleiotropic effects of retinoids are likely to be mediated by nuclear retinoic acid receptors (RAR) acting as ligand-dependent enhancer factors. However, in previous studies we have been unable to document altered RAR expression at the RNA level in response to retinoic acid (RA) treatment or in psoriatic lesions, conditions characterized by marked alterations in keratinocyte proliferation and differentiation, which are either caused by or responsive to RA. In an attempt to identify other potential regulators of RA responsiveness, we have used RNA blot hybridization to study the expression of the cellular retinoic acid binding proteins (CRABP) CRABP-I and CRABP-II, the RAR-gamma isoforms RAR-gamma 1 and RAR-gamma 2, and the low-affinity RAR homologue RXR in normal, RA-treated, and psoriatic human epidermis. CRABP-II is selectively and markedly induced by RA in adult human skin (J Biol Chem 266:17662-17666, 1991). However, in submerged, serum-free keratinocyte cultures, CRABP-II mRNA could not be induced by RA. Comparisons of intact human skin, submerged keratinocyte cultures, and human skin equivalent cultures indicated that induction of CRABP-II by RA requires epidermal stratification, dermal-epidermal interactions, or both. CRABP-II transcripts were also expressed in heat-separated human dermis at levels similar to those found in epidermal keratome biopsies, whereas CRABP-I transcripts were undetectable in dermal RNA. CRABP-II transcripts were markedly elevated in psoriatic lesions, as they were in RA-treated skin. In contrast, CRABP-I mRNA was undetectable and not increased in psoriatic lesions. Expression of RAR-gamma isoforms and RXR was not detectably altered in either psoriatic lesions or in RA-treated skin. Thus, altered expression of CRABP-II appears more likely to regulate the cutaneous actions of RA than does altered expression of CRABP-I, RXR, or RAR-gamma isoforms. From these and other results, a model for regulation of RA action involving sequestration of RA by CRABP-II is proposed.

Chromosomal assignment of retinoic acid receptor (RAR) genes in the human, mouse, and rat genomes

The human genes encoding the alpha and beta forms of the retinoic acid receptor are known to be located on chromosomes 17 (band q21.1:RARA) and 3 (band p24:RARB). By in situ hybridization, we have now localized the gene for retinoic acid receptor gamma, RARG, on chromosome 12, band q13. We also mapped the three retinoic acid receptor genes in the mouse, by in situ hybridization, on chromosomes 11, band D (Rar-a); 14, band A (Rar-b); and 15, band F (Rar-g), respectively, and in the rat, using a panel of somatic cell hybrids that segregate rat chromosomes, on chromosomes 10 (RARA), 15 (RARB), and 7 (RARG), respectively. These assignments reveal a retention of tight linkage between RAR and HOX gene clusters. They also establish or confirm and extend the following homologies: (i) between human chromosome 17, mouse chromosome 11, and rat chromosome 10 (RARA); (ii) between human chromosome 3, mouse chromosome 14, and rat chromosome 15 (RARB); and (iii) between human chromosome 12, mouse chromosome 15, and rat chromosome 7 (RARG).

Retinoic acid-induced glandular metaplasia in mouse skin is linked to the dermal expression of retinoic acid receptor beta mRNA

The distribution of transcripts of nuclear (RAR alpha, RAR beta, and RAR gamma) and cytosolic (CRABP) retinoic acid receptors was analyzed in 13.5-day mouse embryo upper-lip skin, cultured in vitro for 48 hr with or without added retinoic acid. The results show a significant up-regulation of the transcription of the RAR beta gene concomitant with the initiation of an alteration of hair vibrissae follicle development, leading, after transfer for 8 days to the chick embryo chorioallantoic membrane, to an exocrine-type gland morphogenesis.

Retinoic acid receptor gene expression in human skin

Human skin exhibits a characteristic, pleiotypic response to topical retinoic acid. In attempting to understand this response at the molecular level, we have used fast protein liquid chromatography (FPLC) and RNA blot hybridization to characterize the expression of the nuclear retinoic acid receptor (RAR) alpha, beta, and gamma genes in adult human epidermis. Size exclusion FPLC of 0.6 M NaCl nuclear extracts prepared from keratome biopsies revealed two peaks of specific [3H] retinoic acid (RA) binding at Mr 45 and 18 kDa, in agreement with the expected sizes of RAR and cellular RA binding protein. Blot hybridization analysis of total RNA extracted from keratome biopsies revealed that RAR-gamma was the predominant RAR species expressed in human epidermis, as RAR-alpha transcripts were detectable only at low levels and RAR-beta transcripts were undetectable. RAR transcripts were not induced by topical treatment with 0.1% RA cream under occlusion for 4 h or 4 d. Moreover, there was no significant difference in RAR-gamma transcript levels in normal and psoriatic epidermis. RAR-gamma transcripts were constitutively expressed not only in cultured human keratinocytes, but also in human dermal and lung fibroblasts. RAR-beta was induced by RA in dermal fibroblasts, but not in keratinocytes. RA induced IL-1 beta transcripts in keratinocytes rapidly (2 to 4 h) and at low concentrations (3 x 10(-10) M), consistent with activation of the IL-1 beta gene via RAR. These results demonstrate constitutive expression of RAR-gamma in human epidermis, and suggest that RAR-gamma is a molecular target of RA action in adult human skin.

Multiple isoforms of the mouse retinoic acid receptor alpha are generated by alternative splicing and differential induction by retinoic acid

Together with the previously described mouse retinoic acid receptor alpha-1 (mRAR-alpha 1, formerly mRAR-alpha 0), we have isolated and characterized here a total of seven mRAR-alpha cDNA isoforms (mRAR-alpha 1 to alpha 7). These isoforms are generated from mRAR-alpha primary transcript(s) of a single gene by alternative splicing of at least eight different exons with the exon which encodes the amino acid sequence of their common B region. All of these isoforms differ in their 5'-untranslated regions (5'-UTRs) and, in the case of mRAR-alpha 1 and alpha 2, also in the sequences encoding the N-terminal A region which is known to be important for differential trans-activation by other members of the nuclear receptor superfamily. In addition, the sequences encoding the open reading frames (ORFs) of mRAR-alpha 3 and alpha 4 cDNA isoforms remain open to their very 5' ends, which suggests that these two isoforms may also encode RAR-alpha s with unique A region amino acid sequences. The two predominant isoforms, mRAR-alpha 1 and alpha 2, were found to be differentially expressed in mouse adult and fetal tissues, as well as in P19 and F9 embryonal carcinoma (EC) cell lines. Interestingly, the expression of mRAR-alpha 2, in contrast to that of the mRAR-alpha 1 isoform, was induced by retinoic acid (RA) in EC cells, thus suggesting the presence of two promoters in the 5' region of the mRAR-alpha gene, which differ in their response to RA. The conservation between mouse and human RAR-alpha 1 and alpha 2 cDNA isoform sequences, as seen by cross-hybridization in Southern blots or by DNA sequence analysis, together with their differential patterns of expression, strongly suggests that they perform specific functions during embryogenesis and in the adult.

Differentially expressed isoforms of the mouse retinoic acid receptor beta generated by usage of two promoters and alternative splicing

Using anchored PCR, three different cDNA isoforms of the mouse retinoic acid receptor beta [mRAR-beta 1, mRAR-beta 2 (formerly mRAR-beta 0) and mRAR-beta 3], generated from the same gene by differential promoter usage and alternative splicing, were isolated. These three isoforms encode RAR proteins with different N-terminal A regions and identical B - F regions. The sequence encoding the first 59 amino acids of the mRAR-beta 3 A region is identical with the entire A region of mRAR-beta 1. However, the sequence of mRAR-beta 3 region A differs from that of mRAR-beta 1 by an additional 27 C-terminal amino acids encoded in an 81 nucleotide-long putative exon which is spliced in between the exons encoding the A and B regions of mRAR-beta 1. Both mRAR-beta 1 and beta 3 cDNAs differ entirely from mRAR-beta 2 in their 5'-untranslated (5'-UTR) and A region coding sequences. This N-terminal variability, in a region which was shown to be important for cell-type specific differential target gene trans-activation by other nuclear receptors, suggests that the three mRAR-beta isoforms may be functionally distinct. The conservation of RAR-beta isoform sequences from mouse to human, as seen by cross-hybridization on Southern blots or DNA sequence analysis, as well as their differential patterns of expression in various mouse tissues, corroborates this view. Additionally, the mRNA analysis data suggest that mRAR-beta 2, whose expression predominates in RA-treated embryonal carcinoma (EC) and embryonic stem (ES) cells, may be important during early stages of development. mRAR-beta 1 and beta 3, on the other hand, which are predominantly expressed in fetal and adult brain, may play some specific role in the development of the central nervous system.

Retinoic acid and synthetic analogs differentially activate retinoic acid receptor dependent transcription

We have developed an assay where the potency of retinoids in retinoic acid receptor (RAR) mediated transcriptional activation can be rapidly evaluated. In this assay hRAR-alpha, hRAR-beta and hRAR-gamma were expressed in CV-1 cells together with a reporter gene containing a retinoic acid responsive element (TRE3-tk-CAT). Concentrations required to obtain half-maximum induction (ED50) of CAT-activity were determined for several retinoids, e.g., all-trans-retinoic acid (RA), 13-cis-retinoic acid (13-cis-RA), arotinoid acid (TTNPB) and m-carboxy-arotinoid acid (m-carboxy-TTNPB, an inactive arotinoid analog). The ED50 values for RA decreased in the order of RAR-alpha (24 nM) greater than RAR-beta (4.0 nM) greater than RAR-gamma (1.3 nM), while the ED50 values for TTNPB and 13-cis-RA decreased in the order of RAR-alpha (6.5 nM, 190 nM) greater than RAR-gamma (2.3 nM, 140 nM) greater than RAR-beta (0.6 nM, 43 nM), respectively. No significant inductions were obtained when cells were treated with m-carboxy-TTNPB, even at 10 microM concentrations. The fold induction of CAT-activity for all compounds tested decreased in the order of RAR-alpha greater than RAR-beta greater than RAR-gamma.

Two distinct estrogen-regulated promoters generate transcripts encoding the two functionally different human progesterone receptor forms A and B

The human progesterone receptor (hPR) cDNA, synthesized from T47D breast cancer cells, and the hPR gene 5'-flanking region were cloned and sequenced. Comparison of the cDNA-deduced amino acid sequence with other PR homologues demonstrated the modular structure characteristic of nuclear receptors. As in the case of the chicken homologue, there are two hPR forms, A and B, which originate from translational initiation at AUG2 (codon 165) and AUG1, respectively. Northern blot analysis of T47D mRNA using various cDNA derived probes identified two classes of hPR mRNAs, one of which could code for hPR form B, while the other one lacked the 5' region upstream of AUG1. S1 nuclease mapping and primer extension analyses confirmed that the second class of hPR transcripts are initiated between +737 and +842 and thus encode hPR form A, but not form B. By using the hPR gene 5'-flanking sequences as promoter region in chimeric genes, we show that a functional promoter (located between -711 and +31) directs initiation of hPR mRNAs from the authentic start sites located at +1 and +15. Most importantly, initiation of transcription from chimeric genes demonstrated the existence of a second promoter located between +464 and +1105. Transient co-transfection experiments with vectors expressing the human estrogen receptor showed that both promoters were estrogen inducible, although no classical estrogen responsive element was detected in the corresponding sequences. When transiently expressed, the two hPR forms similarly activated transcription from reporter genes containing a single palindromic progestin responsive element (PRE), while form B was more efficient at activating the PRE of the mouse mammary tumor virus long terminal repeat. Transcription from the ovalbumin promoter, however, was induced by hPR form A, but not by form B.

Murine isoforms of retinoic acid receptor gamma with specific patterns of expression

We have characterized seven murine retinoic acid receptor gamma cDNA isoforms (mRAR-gamma 1 to -gamma 7) generated by alternative splicing of at least seven exons. These isoforms differ from one another in their 5' untranslated region and in two cases (mRAR-gamma 1 and -gamma 2) differ in their N-terminal A region, which is known to be important for differential transactivation by other nuclear receptors. mRAR-gamma 1 and -gamma 2, the predominant isoforms, are differentially expressed in adult tissues and during embryogenesis. Most notably, skin contains almost exclusively mRAR-gamma 1 transcripts. The conservation of the RAR-gamma isoforms from mouse to human together with their patterns of expression suggests that they perform specific functions, which may account for the pleiotropic effect of retinoic acid in embryogenesis and development.

Receptor interconversion model of hormone action. 3. Estrogen receptor mediated repression of reporter gene activity in A431 cells

The chicken estrogen receptor exists in three interconvertible forms, two of which bind estradiol with high affinity and one which lacks the capacity to bind estradiol. Interconversion is regulated by reactions involving ATP/Mg2+. By cotransfecting into A431 cells estrogen receptor cDNA in an expression vector together with the pA2 (-821/-87) tk-CAT vitellogenin construct, we demonstrate that constitutive expression of chloramphenicol acetyltransferase (CAT) activity can be regulated either by selection of ligand or by modifying phosphorylation reactions in the recipient cells. In the presence of estrogen receptors, constitutive expression of CAT activity is inhibited in three situations: (i) in the absence of an estrogenic ligand; (ii) in the presence of an anti-estrogen; and (iii) in the presence of an estrogenic ligand together with 12-O-tetradecanoylphorbol 13-acetate (TPA). Estrogen receptor mediated repression of constitutive CAT activity is not observed with the pA2 (-331/-87) tk-CAT construct, indicating that DNA sequences required for repression are located between -821 and -331 base pairs upstream of the transcription initiation site.

Specific spatial and temporal distribution of retinoic acid receptor gamma transcripts during mouse embryogenesis

Retinoic acid (RA), a putative morphogen in vertebrates, has profound effects on development during embryogenesis, chondrogenesis and differentiation of squamous epithelia. The distribution of the transcripts of the retinoic acid receptor gamma (RAR-gamma) gene has been studied here by in situ hybridization during mouse development from days 6.5 to 15.5 post-coitum (p.c.). RAR-gamma transcripts are detected as early as day 8 p.c. in the presomitic posterior region. Between days 9.5 and 11.5 p.c., the transcripts are uniformly distributed in the mesenchyme of the frontonasal region, pharyngeal arches, limb buds and sclerotomes. At day 12.5 p.c., RAR-gamma transcripts are found in all precartilaginous mesenchymal condensations. From day 13.5 p.c., the transcripts are specifically localized in all cartilages and differentiating squamous keratinizing epithelia, irrespective of their embryological origin. RAR-gamma transcripts are also found in the developing teeth and whisker follicles. The developmental pattern of expression of the RAR-gamma gene suggests that RAR-gamma plays a crucial role for transducing RA signals at the level of gene expression during morphogenesis, chondrogenesis and differentiation of squamous epithelia.

Expression and estrogen regulation of progesterone receptor mRNA in neurons of the mediobasal hypothalamus: an in situ hybridization study

Diverse effects of steroid hormones on different tissues result from the tissue-specific regulation of target gene expression by steroid hormone receptors. These receptors belong to a family of transacting factors that regulate transcriptional activation of target genes by binding to DNA recognition sequences located in the 5'-flanking region of the target gene. In the brain, receptors for the gonadal steroid hormones estrogen (E) and progesterone (P) are present in discrete neuronal populations. These steroid hormone receptor-containing neurons mediate the effects of the gonadal steroids on a number of neural processes, including reproductive behavior. Using in situ hybridization we have found progesterone receptor (PR) mRNA-containing neurons present in specific hypothalamic nuclei and in the amygdala. E regulates PR mRNA levels in specific neuronal cell groups which express both ER and PR (in basomedial hypothalamus), but not in others (medial amygdala). The E-induced increase in P-responsive neurons in ventromedial hypothalamus can account for the permissive influence of E on P-facilitated reproductive behavior. This is the first demonstration that synthesis of a transcription factor (PR) can be related to a mammalian behavior.

A third human retinoic acid receptor, hRAR-gamma

Retinoic acid receptors (RARs) are retinoic acid (RA)-inducible enhancer factors belonging to the superfamily of steroid/thyroid nuclear receptors. We have previously characterized two human RAR (hRAR-alpha and hRAR-beta) cDNAs and have recently cloned their murine cognates (mRAR-alpha and mRAR-beta) together with a third RAR (mRAR-gamma) whose RNA was detected predominantly in skin, a well-known target for RA. mRAR-gamma cDNA was used here to clone its human counterpart (hRAR-gamma) from a T47D breast cancer cell cDNA library. Using a transient transfection assay in HeLa cells and a reporter gene harboring a synthetic RA responsive element, we demonstrate that hRAR-gamma cDNA indeed encodes a RA-inducible transcriptional trans-activator. Interestingly, comparisons of the amino acid sequences of all six human and mouse RARs indicate that the interspecies conservation of a given member of the RAR subfamily (either alpha, beta, or gamma) is much higher than the conservation of all three receptors within a given species. These observations indicate that RAR-alpha, -beta, and -gamma may perform specific functions. We show also that hRAR-gamma RNA is the predominant RAR RNA species in human skin, which suggests that hRAR-gamma mediates some of the retinoid effects in this tissue.

Cloning of murine alpha and beta retinoic acid receptors and a novel receptor gamma predominantly expressed in skin

In addition to having profound effects on embryonic pattern formation, retinoic acid (RA) has striking effects on differentiation and maintenance of epithelial cells in vivo and in vitro Skin is a major target organ for retinoids both in its normal and pathological states. The discovery of two human nuclear receptors for RA (hRAR alpha and hRAR beta) acting as transcriptional RA-inducible enhancer factors has provided a basis for understanding how RA controls gene expression. To investigate the specific role that RARs might play during development and in adult tissues, we have cloned the mouse RAR alpha and RAR beta (mRAR alpha and mRAR beta). Their amino-acid sequences are much more homologous to those of hRAR alpha and hRAR beta, respectively, than to each other, which suggests strongly that RAR alpha- and beta-subtypes have different functions. Most interestingly we have discovered a novel RAR subtype (mRAR gamma) whose expression in adult mouse seems to be highly restricted to skin, whereas RAR alpha and RAR beta are expressed in a variety of adult tissues. Furthermore, both mRAR alpha and mRAR gamma RNAs are readily detected in undifferentiated F9 embryocarcinoma (EC) cells, whereas mRAR beta messenger RNA is induced at least 30-fold in RA-differentiated F9 cells.

Identification of a second human retinoic acid receptor

We have previously described a human complementary DNA that encodes a novel protein which is homologous to members of the steroid/thyroid nuclear receptor multigene family. This novel protein (hap for hepatoma) exhibits strong homology with the human retinoic acid receptor (RAR) which has been recently characterized. To test the possibility that the hap protein might also be a retinoid receptor, a chimaeric receptor was created by replacing the putative DNA binding domain of hap with that of the human oestrogen receptor (ER). The resulting hap-ER chimaera was then tested for its ability to trans-activate an oestrogen-responsive reporter gene (vit-tk-CAT) in the presence of possible receptor ligands. Here we show that retinoic acid (RA) at physiological concentrations is effective in inducing the expression of this reporter gene by the hap-ER chimaeric receptor. This demonstrates the existence of two human retinoic acid receptors designated RAR-alpha and RAR-beta.

Assignment of the human progesterone receptor to the q22 band of chromosome 11

The human progesterone receptor gene was localized by in situ hybridization to the q22 band of chromosome 11.

A human retinoic acid receptor which belongs to the family of nuclear receptors

A cDNA encoding a protein that binds retinoic acid with high affinity has been cloned. The protein is homologous to the receptors for steroid hormones, thyroid hormones and vitamin D3, and appears to be a retinoic acid-inducible trans-acting enhancer factor, suggesting that the molecular mechanisms of the effect of retinoids (vitamin A) on embryonic development, differentiation and tumour cell growth are similar to those described for other members of this nuclear receptor family.

Specific expression of the pS2 gene in subclasses of breast cancers in comparison with expression of the estrogen and progesterone receptors and the oncogene ERBB2

The expression of the pS2 gene, which is induced by estrogen in the breast cancer cell line MCF-7, has been investigated in breast cancers by using pS2 mRNA determination in tumor specimens and immunocytochemistry to identify pS2 protein in paraffin-embedded sections. Using these assays we show that determination of pS2 gene expression allows the definition of subclasses of estrogen-receptor-containing breast cancers that may be used to more precisely identify estrogen-dependent tumors. Tumor specimens have also been analyzed for the presence of mRNAs for the estrogen receptor and for the ERBB2 oncogene. No evidence for the presence of truncated forms of estrogen-receptor mRNA has been found, and overexpression of the ERBB2 oncogene did not correlate with the steroid receptor status or pS2 gene expression.

Developmental regulation of the estrogen receptor and the estrogen responsiveness of five yolk protein genes in the avian liver

The magnitude of the expression of five yolk protein genes in the avian liver in response to exogenous estradiol is shown to be developmentally regulated. Though each of these yolk protein genes gains the capacity to respond to estradiol during embryonic development, we demonstrate that maximal responses for the different genes are achieved at distinct ages between 1 and 6 weeks after hatching. This observation prompted us to look for possible correlations between yolk protein gene expression and changes in the expression of estrogen receptors that might also occur after hatching. We discovered that indeed the maximal level of nuclear estrogen receptors (assayed following the administration of estradiol) increases progressively over this same period of development from approximately 1000 receptors per cell at 1 week after hatching to approximately 3500 receptors per cell at 6 weeks after hatching. The latter number represents the fully mature state, as comparable levels of receptors are present in the livers of egg-laying hens. Thus, though increases in the expression of estrogen receptors during embryonic liver development have previously been reported, our results indicate that the changes that occur after hatching are quantitatively far more significant to the developmental program for this transcription factor.

Characterization of the estrogen-induced pS2 protein secreted by the human breast cancer cell line MCF-7

Our laboratory has reported previously the cloning of a complementary DNA termed pS2, corresponding to a messenger RNA (mRNA) whose synthesis is induced by estrogen in the human breast cancer cells MCF-7. Examination of the possible open reading frames of this complementary DNA has led to the prediction that the pS2 protein could be a secreted polypeptide of either 58 or 63 amino acids in length. Using a rabbit antiserum prepared against a synthetic peptide corresponding to the last 31 amino acids of the putative protein, we show that a protein with the expected migration during sodium dodecyl sulfate gel electrophoresis can indeed be immunoprecipitated from either the culture medium of MCF-7 cells grown in the presence of labeled amino acids or the in vitro translation products of MCF-7 poly(A) RNA enriched in pS2 mRNA. Furthermore, in vivo and in vitro differential amino acid labeling allows us to conclude that the mature pS2 protein is probably secreted as a 58 amino acid long peptide. Finally, we show that pS2 protein synthesis is induced in MCF-7 cells by estradiol and phenol red, but not by the antiestrogen tamoxifen, in keeping with our previous results demonstrating estrogen induction of pS2 mRNA synthesis.

Cloning of the chicken progesterone receptor

Monospecific antibodies directed against the chicken progesterone receptor (PR) form B were used to screen a randomly primed phage lambda gt11 cDNA expression library prepared from size-fractionated chicken oviduct mRNA. Two independent immunoreactive clones, lambda cPR1 and lambda cPR2, were isolated. Antibodies selected from anti-PR form B antiserum on matrices of lambda cPR1 and lambda cPR2 fusion proteins detected two proteins on electrophoretic immunoblots of crude and purified PR preparations. These proteins had the same apparent molecular weights as did PR forms A and B crosslinked with the tritiated progestin R 5020. Thus, lambda cPR1 and lambda cPR2 fusion proteins contain epitopes present in both PR forms A and B. A cDNA clone, lambda cPR3, containing the inserts of both lambda cPR1 and lambda cPR2, was isolated from a randomly primed lambda gt10 oviduct cDNA library, indicating that both cDNA inserts were derived from the same oviduct mRNA. Additional evidence that these cDNAs correspond to PR mRNA was provided by sequencing the lambda cPR3 cDNA insert, since it was found to encode the sequence of three tryptic peptides prepared from purified PR form B. A fourth and a fifth cDNA clone, lambda cPR4 and lambda cPR5, were sequentially isolated from the same lambda gt10 cDNA library beginning with a probe derived from the 3' end of the lambda cPR3 insert. Partial DNA sequencing of lambda cPR4 and lambda cPR5 revealed the presence of a sequence coding for a cysteine-rich domain that is strikingly homologous to the amino acid sequences present in the putative DNA-binding domain of the human and chicken estrogen receptors, human glucocorticoid receptor, and v-erbA gene product of the avian erythroblastosis virus.

The chicken oestrogen receptor sequence: homology with v-erbA and the human oestrogen and glucocorticoid receptors

A chicken oviduct cDNA clone containing the complete open reading frame of the oestrogen receptor (ER) has been isolated and sequenced. The mol. wt of the predicted 589-amino acid protein is approximately 66 kd which is very close to that of the human ER. Comparison of the human and chicken amino acid sequences shows that 80% of their amino acids are identical. There are three highly conserved regions; the second and third of which probably represent the DNA- and hormone-binding domains of the receptor. The putative DNA-binding domain is characterised by its high cysteine and basic amino acid content, and the hormone-binding domain by its overall hydrophobicity. These two domains of homology are also present in the human glucocorticoid receptor (GR) and the product of the avian erythroblastosis virus (AEV) gene, v-erbA, indicating that c-erbA, the cellular counterpart of v-erbA, belongs to a multigene family of transcriptional regulatory proteins which bind steroid-related ligands. The first highly conserved ER region is not present in the truncated v-erbA gene, but shares some homology with the N-terminal end of the GR. The function of the v-erbA gene product is discussed in relation to its homology with the ER and GR sequences.

Human oestrogen receptor cDNA: sequence, expression and homology to v-erb-A

We have cloned and sequenced the complete complementary DNA of the oestrogen receptor (ER) present in the breast cancer cell line MCF-7. The expression of the ER cDNA in HeLa cells produces a protein that has the same relative molecular mass and binds oestradiol with the same affinity as the MCF-7 ER. There is extensive homology between the ER and the erb-A protein of the oncogenic avian erythroblastosis virus.

Cloning of the human oestrogen receptor cDNA

Poly A+ RNA isolated from the human breast cancer cell line MCF-7 was fractionated by sucrose gradient centrifugation and those fractions enriched in oestrogen receptor (ER) mRNA were used to prepare randomly primed cDNA libraries in the lambda gt11 vectors. Clones corresponding to the ER were isolated from both libraries after screening with either ER monoclonal antibodies (lambda gt11) or synthetic oligonucleotide probes designed from two peptide sequences of purified ER (lambda gt10). Five cDNA clones were isolated by antibody screening and five after screening with synthetic oligonucleotides. The two largest ER cDNA clones, lambda OR3 (1.3 kbase) and lambda OR8 (2.1 kbase), isolated using antibodies and oligonucleotides, respectively, were able to enrich selectively for ER mRNA by hybrid-selection. Furthermore, lambda OR8 contains DNA sequences which cross-hybridize with each of the other ER cDNA clones. These results demonstrate that the clones isolated correspond to the ER mRNA sequence. Using lambda OR8 as a hybridization probe revealed a single poly A+ RNA band of approx. 6.2 kbase in the ER containing human breast cancer cell lines MCF-7 and T47D. In contrast, no hybridization was seen in the human ER-cell line HeLa. The same probe hybridizes to a chicken gene which is expressed in oviduct tissue as a 7.5 kbase poly A+ RNA.

Cloning of the human estrogen receptor cDNA

Poly(A)+ RNA isolated from the human breast cancer cell line MCF-7 was fractionated by sucrose gradient centrifugation and fractions enriched in estrogen receptor (ER) mRNA were used to prepare randomly primed cDNA libraries in the lambda gt10 and lambda gt11 vectors. Clones corresponding to ER sequence were isolated from both libraries after screening with either ER monoclonal antibodies (lambda gt11) or synthetic oligonucleotide probes designed from two peptide sequences of purified ER (lambda gt10). Five cDNA clones were isolated by antibody screening and five were isolated after screening with synthetic oligonucleotides. The two largest ER cDNA clones, lambda OR3 (1.3 kilobase pairs) and lambda OR8 (2.1 kilobase pairs), isolated by using antibodies and oligonucleotides, respectively, were able to enrich selectively for ER mRNA by hybrid-selection. Furthermore, lambda OR8 contains the DNA sequence expected from the two ER peptides and crosshybridizes with each of the other ER cDNA clones. These results demonstrate that the clones isolated correspond to the ER mRNA sequence. Use of lambda OR8 as a hybridization probe revealed a single poly(A)+ RNA band of approximately equal to 6.2 kilobase pairs in the ER-containing human breast cancer cell lines MCF-7 and T47D. In contrast, no hybridization was seen in the human ER-negative cell line HeLa. The same probe hybridizes to a chicken gene that is expressed in oviduct tissue as a 7.5-kilobase-pair poly(A)+ RNA.

Effects of antiestrogens on the estrogen-regulated pS2 RNA and the 52- and 160-kilodalton proteins in MCF7 cells and two tamoxifen-resistant sublines

The effects of estradiol and antiestrogens on two estrogen-regulated proteins (52 and 160 kDa) and an estrogen-inducible mRNA (pS2) have been measured in the MCF7 human breast cancer cell line and two tamoxifen-resistant sublines. In MCF7 cells, tamoxifen (or nafoxidine) alone does not significantly affect pS2 mRNA levels nor transcription of the pS2 gene but completely antagonizes the ability of estradiol to increase pS2 RNA levels. The estrogen-mediated increase in pS2 mRNA levels resembles that of two estrogen-regulated proteins (52 and 160 kDa) that are released from MCF7 cells into the culture medium. This is distinct from the estrogen-mediated increase in progesterone receptor which is also obtained by tamoxifen treatment. In the two tamoxifen-resistant sublines (R27 and RTx6), tamoxifen does not increase pS2 mRNA levels or 160-kDa protein production but increases the production of the 52-kDa protein. These results show that in these tamoxifen-resistant cells, tamoxifen has become fully estrogenic for one, but not all estrogen-regulated responses.

Cloning of cDNA sequences of hormone-regulated genes from the MCF-7 human breast cancer cell line

cDNA clones corresponding to a mRNA whose level is rapidly increased by addition of oestradiol to the culture medium have been isolated by differential screening of a cDNA library from the breast cancer cell line MCF-7, which contains oestrogen receptors. Such clones will be useful in studies of the DNA sequences required for hormonal induction and to determine whether expression of the corresponding gene is in any way related to the cancerous state. We have also obtained a cDNA clone for a messenger whose level is apparently decreased by steroid hormones.

Adult chicken alpha-globin genes alpha A and alpha D: no anemic shock alpha-globin exists in domestic chickens

Three alpha-type globin genes have been identified in the alpha-globin linkage group of chickens. No other alpha-type genes hae been directly shown to be within 10 kilobase pairs of any of these three closely linked genes. These three genes have been conclusively identified by DNA sequence analysis. The gene at the 5' end of the linkage group is an embryonic alpha-type globin gene, pi or pi', and the central gene corresponds to the minor adult alpha- globin, alpha D. The 3'-terminal gene sequence corresponds to the sequence of cDNA clones previously described as "alpha S", presumed anemic shock-induced alpha-globin gene [Salser, W. A., Cummings, I., Liu, A., Strommer, J., Padayatty, J. & Clarke, P. (1979) in Cellular and Molecular Regulation of Hemoglobin Switching, eds. Stamatoyannopoulos, G. & Nienheis, A. (Grune and Stratton, New York), pp. 621-643; Richards, R. I. & Wells, J. R. E. (1980) J. Biol. Chem. 255, 9306-9311]. Several groups of workers have isolated alpha S-type cDNA clones but no one has identified a cDNA clone corresponding to the published amino acid sequence of the major chicken alpha-globin, alpha A. We have identified the alpha S-type sequence as the only abundant alpha-like globin sequence in cDNA clones made from reticulocyte mRNA isolated from nonanemic chickens. Therefore, we suggest that the alpha S-type sequence corresponds to the true alpha A-globin species.

Restriction mapping of cDNA recombinants including the adult chicken and duck globin messenger sequences: a comparative study

A comparison of the organization of six avian adult globin messenger sequences is based on previously reported recombinant duck adult globin cDNA plasmids (Therwath et al., 1980) and the actual construction and characterization of pBR322 recombinant plasmids including the beta and the normal alpha A and alpha D chicken adult globin mRNA sequences. Identification of the cloned DNA was performed using hybridization-selection under conditions permitting complete purification in one step of the three globin mRNAs, and translation of the corresponding mRNA. Orientation of the globin insert in the vector was determined, taking into account the computer prediction of the restriction sites based on the known amino acid sequences of the three globin chains (Roizès and Pelaquier, 1980) and those actually observed, and by identification of restriction fragments using 3'-specific probes. Identification, orientation and restriction mapping of these cloned DNAs reveals extensive homologies in organisation of beta sequences between duck and chicken, as well as among the alpha sequences in every two possible combinations.