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Biomedical subjects

V Giguere

Publications and source records attributed to V Giguere.

At least 19 recordsLinked to original sources
PubMed2001

Modulation of retinal cell populations and eye size in retinoic acid receptor knockout mice.

PURPOSE: The retinoic acid receptors are expressed from early stages of development in the diverse tissues that make up the vertebrate eye. Their loss has subtle effects on eye development. We adapted sensitive quantitative trait locus (QTL) mapping methods to assess consequences of inactivating alleles of the alpha and beta receptors, Rara and Rarb, on eye and retinal development. Rara is of particular interest because this gene is a candidate for Nnc1, a QTL that controls retinal ganglion cell proliferation. METHODS: We studied lines of mice in which expression of the a1 isoform of Rara or all isoforms of Rarb had been disrupted by gene targeting. We measured eye weight, lens weight, retinal area, and retinal ganglion cell number in each of six genotypes (Rara and Rarb -/-, +/-, +/+; 10-25 cases/genotype). RESULTS: Loss of either protein is associated with a small but significant loss of eye weight and retinal area. However, only the Rarb knockout has a significant effect on the ganglion cell population and the loss of both wildtype alleles leads to an 8,000 cell deficit. Surprisingly, loss of the Rara a1 isoform that is expressed in this cell population from early stages has no effect on number. Null alleles of both genes have little if any effect on lens growth. CONCLUSIONS: Despite its expression in embryonic retina, Rara is unlikely to be the Nnc1 QTL. In contrast, Rarb, a gene that maps to Chr 14 and which is not an Nnc1 candidate gene, has a significant effect on cell number and is therefore a QTL controlling this key population. This raises the intriguing possibility that normal allelic variants of Rarb modulate the ganglion cell population in other vertebrates, including humans.

Animals↗
PubMed2001

Weathering the storm of perinatal bereavement via hardiness.

Hardiness is a personal resource that can potentially diminish negative effects of life stress. To increase understanding of the role that it can have on the health protection and promotion of bereaved parents following a perinatal loss, this article uses J. Wilson's (1969) method to present a concept analysis of hardiness. This analysis provides not only a fresh perspective for understanding the experience of perinatal loss but has also induced the development of a hardiness instrument. Knowledge development in this area is paramount for professionals interested in enabling bereaved parents to draw on and develop their hardiness, not only to transcend the experience but ultimately to gain a sense of personal growth following their loss.

Adaptation, Psychological↗
PubMed2001

4-Hydroxytamoxifen is an isoform-specific inhibitor of orphan estrogen-receptor-related (ERR) nuclear receptors beta and gamma.

Selective estrogen receptor modulators (SERMs) are synthetic molecules that exhibit tissue-specific activities. 4-hydroxytamoxifen (OHT) is a first generation SERM that functions as an antagonist in breast cancer cells but displays estrogen-like activities in the uterus and bone. The estrogen-receptor-related receptors (ERR) alpha, beta and gamma are orphan members of the superfamily of nuclear receptors. While the ERRs do not respond to natural estrogens, these receptors recognize the estrogen response element and have been shown to activate and repress gene expression in the absence of exogenously added ligand. Here we show that OHT disrupts the interaction between the orphan estrogen-receptor-related (ERR) receptors beta and gamma and a coregulator protein and abolishes the constitutive transcriptional activity of these receptors in transient transfection assays. In contrast, OHT has no effect on coregulator/ERR alpha interaction or its transcriptional activity. These results demonstrate the existence of a novel nuclear receptor-based pharmacological pathway that may contribute to the tissue-specific activities of OHT.

Humans↗
PubMed1997

Compartment-selective sensitivity of cardiovascular morphogenesis to combinations of retinoic acid receptor gene mutations.

Several aspects of normal cardiovascular development require signaling by the vitamin A metabolite retinoic acid. We have previously established germ-line mutations in mice in the genes that encode the RAR alpha 1, RAR beta, and RXR alpha retinoic acid receptors as a means of studying the function of these receptors in vivo. Although mutation of RXR alpha results in fetal ventricular defects, the RAR alpha 1 and RAR beta mutations are apparently nonphenotypic in the heart and elsewhere. In this study, we have established and analyzed combinations of these receptor gene mutations. Malformations of the ventricular chamber (chamber hypoplasia and muscular ventricular septal defects), conotruncus (double-outlet right ventricle, transposition, and membranous ventricular septal defects), aortic sac (persistent truncus arteriosus and aorticopulmonary window), and aortic arch-derived arteries were recovered in various combinations of the RAR alpha 1, RAR beta, and RXR alpha gene mutations. Depending on the combination of receptor mutations, selective defects were obtained in specific cardiovascular compartments, suggestive of differential expression or function of each receptor within domains of the developing heart.

Animals↗
PubMed1996

The molecular genetics of retinoic acid receptors: cardiovascular and limb development.

The vitamin A metabolite retinoic acid (RA) is utilized as a signalling molecule in wide variety of developmental processes, defined by defects which occur after nutritional vitamin A deficiency or after exposure to excess vitamin A. We have initiated a genetic analysis of RA function through the establishment of lines of mice which carry germline mutations in the genes which encode retinoid receptors. Defects which result from developmental RA deficiency or excess have been recovered in embryos which are deficient in various combinations of retinoid receptors. In this chapter, our current understanding of the role of RA and retinoid receptors in cardiovascular and limb development are described, as for these our level of understanding is most advanced.

Animals↗
PubMed1991

The functional domains of the murine Thy-1 gene promoter.

The Thy-1 gene promoter resembles a "housekeeping" promoter in that it is located within a methylation-free island, lacks a canonical TATA box, and displays heterogeneity in the 5'-end termini of the mRNA. Using transgenic mice, we show that this promoter does not confer any tissue specificity and is active only in a position-dependent manner. It can only be activated in a tissue-specific manner by elements that lie downstream of the initiation site. We have analyzed the functional domains of the minimal Thy-1 promoter and show that the dominant promoter elements consist of multiple binding sites for the transcription factor Sp1, an inverted CCAAT box, and sequences proximal to the transcription start site. DNase I and gel mobility shift assays show the binding of a number of nuclear factors to these elements, including Sp1 and CP1. Our results show that the structure of this promoter only permits productive interactions of the two transcription factors Sp1 and CP1 with the basal transcription machinery in the presence of enhancer sequences.

Animals↗
PubMed1988

Retinoic acid and thyroid hormone induce gene expression through a common responsive element.

Studies of steroid receptors have led to the identification of a superfamily of ligand-inducible regulatory proteins that includes receptors for thyroid hormones and retinoic acid. This family of receptors regulates gene expression through binding to short cis-acting sequences referred to as hormone-response elements. Identification of a functional retinoic acid responsive element is crucial to our understanding of the mechanisms by which retinoic acid receptors activate gene expression and regulate cell differentiation. One impediment to such a study is the absence of any identified gene whose transcription is directly dependent on the receptor-hormone complex. Because the DNA-binding domains of the retinoic acid and thyroid hormone receptors are highly related (62% identical in their amino acid sequences), we have investigated the possibility that the retinoic acid receptor could activate gene expression through a thyroid hormone response element. We now report that a human retinoic acid receptor expressed from cloned complementary DNA or the endogenous retinoic acid receptor present in F9 teratocarcinoma cells can activate gene expression from promoters fused to a natural or synthetic thyroid hormone response element. The product translated in vitro from the human retinoic acid receptor cDNA can bind to a thyroid hormone response element with high affinity. The unexpected implication of these findings is that retinoic acid and thyroid hormones, acting through their respective receptors, could control overlapping gene networks involved in the regulation of vertebrate morphogenesis and homeostasis.

Binding Sites↗
PubMed1988

A region in the steroid binding domain determines formation of the non-DNA-binding, 9 S glucocorticoid receptor complex.

This work was initiated to determine if a specific region of the glucocorticoid receptor determines the formation of the inactive (i.e. non-DNA-binding) 9 S form of the receptor recovered in cytosol preparations. It is known that the murine glucocorticoid receptor of the nti phenotype, which consists of only the carboxyl-terminal 40-kDa peptide containing the DNA-binding and steroid-binding domains separated by a short linker region, is recovered in hypotonic lysates as a 9 S heteromeric complex (Gehring, U., and Arndt, H. (1985) FEBS Lett. 179, 138-142). To further localize the domain required for formation of the 9 S complex, we have determined the sedimentation coefficients of receptors produced in COS-7 cells transfected with several mutants of the human glucocorticoid receptor gene. Deletion of the DNA-binding domain results in a 9 S complex that is somewhat less stable than the wild type receptor during sucrose gradient centrifugation. Deletion of the linker region yields a molybdate-stabilized 9 S complex, but deletion of the entire steroid-binding domain or internal deletion of the amino-terminal two-thirds of this domain yields receptors that are constitutive transcriptional activators and are present in cytosol only in the 4 S form. Taken together, these observations demonstrate that the steroid-binding domain contains the features required for formation of the 9 S heteromeric complex, and they are consistent with the proposal that the steroid-binding domain normally represses receptor function.

Amino Acid Sequence↗
PubMed1988

Transcriptional unit of the murine Thy-1 gene: different distribution of transcription initiation sites in brain.

Structural analysis of the mouse Thy-1.2 gene has shown that the major promoter of the gene is characterized by a tissue-specific DNase I-hypersensitive site and is located within a methylation-free island. The gene is regulated at the transcriptional level, and steady-state mRNA analysis reveals that the previously reported exon Ib contributes at most 5% of the total mRNA. The major promoter uses several transcription initiation sites within a region of 100 base pairs. The frequency of usage of these sites in brain is markedly different from that in other tissues.

Animals↗
PubMed1987

Colocalization of DNA-binding and transcriptional activation functions in the human glucocorticoid receptor.

Using a combination of a transient expression assay and in vitro mutagenesis, we showed previously that the human glucocorticoid receptor (hGR) is composed of a series of discrete functional domains. Here we report the effects of selective deletion of each of these domains on hGR ability to activate transcription of the MTV-CAT fusion gene. Deletion of the immunogenic domain or the entire amino-terminal half of the protein reduces but does not abolish the ability of the hGR to induce transcriptional activation. Somewhat surprisingly, deletion of the steroid-binding domain engenders a constitutively active receptor, revealing that this domain normally represses receptor function. However, the central, cysteine-rich region contains all the information required for both DNA binding and trans-activation. Taken together, these data delineate a core domain in the hGR spanning 88 amino acids that determines both DNA-binding and transcriptional activation functions. This physical linkage distinguishes the glucocorticoid receptor from other described eukaryotic regulatory proteins, where these two functions have been shown to be separable.

Animals↗
PubMed1986

The maintenance of methylation-free islands in transgenic mice.

The Thy-1 gene is expressed in a tissue- and stage-specific pattern and has a typical 1.6kb methylation-free island (MFI) covering about 600bp upstream and downstream of the two alternative first exons. By microinjection of a mouse Thy-1.1/human Thy-1 gene into fertilized eggs, we were able to show that the MFI is restored in the transgenic mice. The flanking sequence became methylated, but the MFI remains unmethylated in all tissues of transgenic mice at different developmental stages tested, irrespective of the site of expression of the gene. There is one exception, in extra-embryonal tissues of 14.5 day embryos a small percentage of the islands were methylated. We conclude that maintenance of the MFI is regulated by cis-acting sequences present within the gene, and indicates that the unmethylated state of the islands is consistent with a necessary but not sufficient condition for expression of the gene.

Animals↗
PubMed1986

Autoimmunity to Thy-1.

Conditions are described for the induction of autoimmunity to Thy-1 and a large panel of monoclonal CBA and AKR autoantibodies has been characterized. These reveal a hitherto unrecognized complexity at the Thy-1 locus and evidence for intragenic control. Epitopes recognized by the autoantibodies differed in species and tissue distribution from alloantigenic determinants but their specificity was confirmed by transfection studies with the cloned Thy-1b gene. The quantitative and qualitative differences in epitope expression between Thy-1a and Thy-1b alleles were inherited as single Mendelian traits and in the absence of recombinants, suggesting translational control.

Animals↗
PubMed1985

Anti-Thy-1 antibody responses evoked by Thy-1 antigen expressed in transfected mouse mastocytoma cells and rat fibroblast.

The mouse genomic Thy-1.1 gene was isolated from a phage library constructed from AKR/J (Thy-1.1) mouse DNA. Partial nucleotide sequence analysis of the coding region showed that it has only a single nucleotide difference from the Thy-1.2 gene, namely that amino acid 89 reads CGA (Arg) in Thy-1.1 and CAA (Glu) in Thy-1.2, corresponding to the amino acid substitutions previously identified. It was subcloned into an SV-40 derived vector for transfection. Transient transfection into HeLa cells gave 2% positive staining by immunofluorescence. The gene in this vector was also co-transfected into L cells and mastocytoma cells (both of Thy-1.2 strain origin) together with the Agpt gene. L-cell clones selected for transformation proved almost negative for Thy-1.1 expression, and any positive clones gradually lost Thy-1.1 antigen expression in culture. On the contrary, all clones of mastocytoma transformants gave a high level of expression after more than 3 months in culture. The mastocytoma transformants were used to study the immunogenicity of Thy-1.1 molecules expressed on transfected cells. They evoked clear anti-Thy-1.1 plaque-forming cell (PFC) responses both in vivo and in vitro. The mastocytoma transformants also proved able to induce a T-dependent anti-Thy-1.1 antibody response in a cell transfer experiment. The immunogenicity of Thy-1.2 molecules on rat fibroblasts was also studied after transfection with a Thy-1.2 gene cosmid. Although Thy-1.2 expression was very low, these transfectants elicited a clear anti-Thy-1.2 PFC response from AKR spleen cells hyperimmunized against CBA thymocytes.

Animals↗
PubMed1984

Interactions between CRF, epinephrine, vasopressin and glucocorticoids in the control of ACTH secretion.

The secretion of ACTH by corticotrophs in the anterior lobe of the rat pituitary gland is under the stimulatory influence of at least three receptors, namely that for peptidic CRF (corticotropin-releasing factor), vasopressin and alpha 1-adrenergic agents. CRF is a potent stimulator of cyclic AMP accumulation as well as adenylate cyclase activity in the rat adenohypophysis, thus suggesting an important role of cyclic AMP as mediator of CRF action on ACTH secretion. Vasopressin causes a 2-fold increase of the stimulatory effect of CRF on ACTH release in rat anterior pituitary cells in culture. The potentiating effects of vasopressin on CRF-induced ACTH release are accompanied by parallel changes of intracellular cyclic AMP levels. Vasopressin, while having no effect on basal cyclic AMP levels, causes a 2-fold increase in CRF-induced cyclic AMP accumulation without affecting the ED50 value of CRF action. ACTH secretion is also stimulated by a typical alpha 1-adrenergic receptor. Epinephrine causes a marked stimulation of ACTH release which is additive to that of CRF. Epinephrine, in analogy with vasopressin, although having no effect alone on basal cyclic AMP levels, causes a marked potentiation of CRF-induced cyclic AMP accumulation. Glucocorticoids cause a near-complete inhibition of epinephrine-induced ACTH secretion within 4 h with the following order of ED50 values: triamcinolone acetonide (0.2 nM) greater than dexamethasone (1.0 nM) much greater than cortisol (11 nM) greater than corticosterone (22 nM). Similar effects are observed for CRF- and vasopressin-induced ACTH release. Although the activity of the pituitary-adrenocortical axis in the rat is highly dependent upon sex steroids, 17 beta-estradiol, 5 alpha-dihydrotestosterone and the pure progestin R5020 have no detectable effect on basal or epinephrine-induced ACTH release, thus illustrating the high degree of specificity of glucocorticoids in their feedback control of ACTH secretion. Moreover, glucocorticoids have no effect on CRF-induced cyclic AMP accumulation, thus indicating that their inhibitory effect is exerted at a step following cyclic AMP accumulation.

Adenylyl Cyclases↗
PubMed1982

Site of calcium requirement for stimulation of ACTH release in rat anterior pituitary cells in culture by synthetic ovine corticotropin-releasing factor.

Synthetic ovine corticotropin-releasing factor (CRF) causes a 6- to 8-fold stimulation of ACTH release and cAMP accumulation in rat anterior pituitary cells in culture at ED50 values of 1 and 4 nM, respectively. Removal of Ca2+ from the incubation medium reduces CRF-induced ACTH release by 70% but have no effect on cyclic AMP accumulation. ACTH release induced by 8-Br-cAMP is inhibited by 65% in the absence of Ca2+. The Ca2+ ionophore A23187 does not alter spontaneous ACTH release. Verapamil, a pharmacological agent that blocks Ca2+ entry into cells, has no influence on spontaneous or CRF-induced ACTH release. The present data clearly demonstrate a role of Ca2+ in CRF action at a step subsequent to cAMP formation and suggest that Ca2+ is mobilized from intracellular stores during CRF stimulation.

Absorption↗