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P Briata

Publications and source records attributed to P Briata.

At least 19 recordsLinked to original sources
PubMed2003

Pituitary homeobox factor 1, a novel transcription factor in the adrenal regulating steroid 11beta-hydroxylase.

Pituitary homeobox 1 (Ptx1/Pitx1) is a homeodomain-containing transcription factor present throughout pituitary development. Ptx1/Pitx1 interacts with steroidogenic factor 1 (SF-1) in the regulation of pituitary gene expression. SF-1 also plays a critical role in the transcription of enzymes involved in adrenal steroidogenesis. Therefore, we analyzed the presence and role of Ptx1/Pitx1 in human adrenal cortex. Both Ptx1/Pitx1 and SF-1 mRNA were expressed in the human adrenal gland, and immuno-electron microscopy demonstrated the presence of Ptx1/Pitx1 protein in the nucleus of adrenocortical cells. Computer analysis revealed the presence of Ptx1/Pitx1 signal sequences within the promoter region of human 11beta hydroxylase ( hCYP11B1). To examine the role of Ptx1/Pitx1 in the regulation of the genes, we prepared reporter constructs using the 5'-flanking DNA of the hCYP11B1 gene and transfected them into Y-1 mouse adrenocortical cells, HeLa and CV-1 cells. Ptx1/Pitx1 stimulation of hCYP11B1 reporter activity (3-fold over basal) in Y-1 cells was equal to that observed with SF-1. The hCYP11B1 promoter activity in Y-1 cells was not synergistically increased by co-transfection with both Ptx1/Pitx1 and SF-1. Both basal and ACTH-stimulated hCYP11B1 reporter activities in Y-1 cells were increased by co-transfection with either Ptx1/Pitx1 or SF-1 expression vectors. In contrast, co-transfection with both Ptx1/Pitx1 and SF-1 synergistically increased hCYP11B1 promoter activity in HeLa and CV-1 cells (5-fold and 20-fold over basal, respectively). In conclusion, this study represents the first demonstration for a role of Ptx1/Pitx1 in the regulation of transcription of enzymes involved in adrenal steroidogenesis.

Adrenal Glands↗
PubMed2000

Multistep signaling and transcriptional requirements for pituitary organogenesis in vivo.

During development of the mammalian pituitary gland, specific hormone-producing cell types, critical in maintaining homeostasis, emerge in a spatially and temporally specific fashion from an ectodermal primordium. We have investigated the molecular basis of generating diverse cell phenotypes from a common precursor, providing in vivo and in vitro evidence that development of these cell types involves at least four sequential phases of signaling events and the action of a gradient at an ectodermal boundary. In the first phase, we hypothesize that this notochord induces invagination of Rathke's pouch from the oral ectoderm. This is followed by appearance of an ectodermal boundary, formed with exclusion of Shh from the nascent pouch. Next, signals from the ventral diencephalon--expressing BMP4, Wnt5a, FGF10, and FGF8--in concert with Shh represent critical in vivo signals for pituitary determination. Subsequently, a dorsal-ventral BMP2 signal gradient emanates from a ventral pituitary organizing center, forming at the boundary to oral ectoderm region from which Shh expression is selectively excluded. In concert with a dorsal FGF8 signal, this creates opposing gradients that generate overlapping patterns of specific transcription factors that underlie cell lineage specification events. The mechanisms by which these transient gradients of signaling molecules lead to the appearance of four ventral pituitary cell types appear to involve the reciprocal interactions of two transcription factors, Pit-1 and GATA-2, which are epistatic to the remainder of the cell type-specific transcription programs and serve as a molecular memory of the transient signaling events. Unexpectedly, this program includes a DNA-binding-independent function of Pit-1, suppressing the ventral GATA-2-dependent gonadotrope program by inhibiting GATA-2 binding to gonadotrope- but not thyrotrope-specific genes. This indicates that both DNA-binding-dependent and-independent actions of abundant determining factors contribute to generate distinct cell phenotypes. In the fourth phase, temporally specific loss of the BMP2 signal is required to allow terminal differentiation. The consequence of these sequential organ and cellular determination events is that each of the pituitary cell types--gonadotropes, thyrotropes, somatotropes, lactotropes, corticotropes, and melanotropes appears to be determined, in a ventral to dorsal gradient, respectively, apparently based on a combinatorial code of transcription factors induced by the gradient of specific signaling molecules.

Animals↗
PubMed1999

Pitx2 regulates lung asymmetry, cardiac positioning and pituitary and tooth morphogenesis.

Pitx1 and Pitx2 are highly homologous, bicoid-related transcription factors. Pitx2 was initially identified as the gene responsible for the human Rieger syndrome, an autosomal dominant condition that causes developmental abnormalities. Pitx2 is asymmetrically expressed in the left lateral-plate mesoderm, and mutant mice with laterality defects show altered patterns of Pitx2 expression that correlate with changes in the visceral symmetry (situs). Ectopic expression of Pitx2 in the right lateral-plate mesoderm alters looping of the heart and gut and reverses body rotation in chick and Xenopus embryos. Here we describe the phenotype of Pitx2 gene-deleted mice, characterized by defective body-wall closure, right pulmonary isomerism, altered cardiac position, arrest in turning and, subsequently, a block in the determination and proliferation events of anterior pituitary gland and tooth organogenesis. Thus, Pitx2 is a transcription factor that encodes 'leftness' of the lung.

Abnormalities, Multiple↗
PubMed1999

Binding properties of the human homeodomain protein OTX2 to a DNA target sequence.

OTX2, a homeodomain protein essential in mouse for the development of structures anterior to rhombomere 3, binds with high affinity to a DNA element (called OTS) present in the human tenascin-C promoter. Here we investigate the binding properties of the full length recombinant human OTX2 and of several deletion mutants to the OTS element. We demonstrate that, upon binding of the protein to its DNA target site, a second molecule of OTX2 is recruited to the complex and that a nearby second binding site is not necessary for this interaction. OTX2 sequences located within a region carboxyl-terminal to the homeodomain are necessary in addition to the homeodomain for binding to DNA. Furthermore, OTX2 dimerization requires the same protein domains necessary for DNA binding.

Animals↗
PubMed1999

OTX2 homeodomain protein binds a DNA element necessary for interphotoreceptor retinoid binding protein gene expression.

Transcription of the human interphotoreceptor retinoid binding protein (IRBP) gene is strictly tissue specific, being restricted to retinal photoreceptors and pinealocytes. We have previously demonstrated that a sequence named A element, in the IRBP promoter is essential for IRBP gene transcription in vivo. Here we demonstrate that the human homeodomain protein OTX2 is present in nuclear extracts of IRBP expressing cells and specifically interacts with the IRBP A promoter element in vitro. OTX2, as well as CRX, a homeodomain protein very similar to OTX2, activates the human IRBP promoter in co-transfection experiments.

Animals↗
PubMed1998

EMX2 protein in the developing mouse brain and olfactory area.

The distribution of EMX2, the protein product of the homeobox gene Emx2, was analyzed in the developing mouse CNS by means of a polyclonal antibody we raised against it. The protein is present in the rostral brain, the olfactory area and a set of scattered cells lying between the nasal pits and the telencephalon. In the cortical neuroepithelium EMX2 is expressed all along the rostro-caudal axis in a graded distribution with a caudal-medial maximum and a rostral-lateral minimum. Anti-EMX2 immunoreactivity is also detectable in Cajal-Retzius cells as well as in apical dendrites of marginal neurons of the cortical plate. We also observe that the EMX2 and EMX1 homeoproteins display complementary expression patterns in olfactory bulbs and amygdaloid complex. Here, they demarcate different neuronal populations, involved in processing olfactory information coming from the vomero-nasal organ and from the main olfactory epithelium, respectively. EMX2 is also detectable in mesencephalic structures, such as the optic tectum and tegmentum. The graded distribution of EMX2 along antero-posterior and medial-lateral axes of the primitive cortex prefigures a role of this protein in the subdivision of the cortex in cytoarchitectonic regions and possibly functional areas, whereas its presence in Cajal-Retzius cells suggests a role in the process of cortical lamination.

Animals↗
PubMed1998

Visceral endoderm-restricted translation of Otx1 mediates recovery of Otx2 requirements for specification of anterior neural plate and normal gastrulation.

Otx1 and Otx2, two murine homologs of the Drosophila orthodenticle (otd) gene, contribute to brain morphogenesis. In particular Otx1 null mice are viable and show spontaneous epileptic seizures and abnormalities affecting the dorsal telencephalic cortex. Otx2 null mice die early in development and fail in specification of the rostral neuroectoderm and proper gastrulation. In order to determine whether Otx1(-/- )and Otx2(-/-) highly divergent phenotypes reflect differences in temporal expression or biochemical activity of OTX1 and OTX2 proteins, the Otx2-coding sequence was replaced by a human Otx1 full-coding cDNA. Homozygous mutant embryos recovered anterior neural plate and proper gastrulation but failed to maintain forebrain-midbrain identities, displaying a headless phenotype from 9 days post coitum (d.p.c.) onwards. Unexpectedly, in spite of the RNA distribution in both visceral endoderm (VE) and epiblast, the hOTX1 protein was synthesized only in the VE. This VE-restricted translation was sufficient to recover Otx2 requirements for specification of the anterior neural plate and proper organization of the primitive streak, thus providing evidence that the difference between Otx1 and Otx2 null mice phenotypes originates from their divergent expression patterns. Moreover, our data lead us to hypothesize that the differential post-transcriptional control existing between VE and epiblast cells may potentially contribute to fundamental regulatory mechanisms required for head specification.

Animals↗
PubMed1997

Implication of OTX2 in pigment epithelium determination and neural retina differentiation.

The expression pattern of Otx2, a homeobox-containing gene, was analyzed from the beginning of eye morphogenesis until neural retina differentiation in chick embryos. Early on, Otx2 expression was diffuse throughout the optic vesicles but became restricted to their dorsal part when the vesicles contacted the surface ectoderm. As the optic cup forms, Otx2 was expressed only in the outer layer, which gives rise to the pigment epithelium. This early Otx2 expression pattern was complementary to that of PAX2, which localizes to the ventral half of the developing eye and optic stalk. Otx2 expression was always observed in the pigment epithelium at all stages analyzed but was extended to scattered cells located in the central portion of the neural retina around stage 22. The number of cells expressing Otx2 transcripts increased with time, following a central to peripheral gradient. Bromodeoxyuridine labeling in combination with immunohistochemistry with anti-OTX2 antiserum and different cell-specific markers were used to determine that OTX2-positive cells are postmitotic neuroblasts undergoing differentiation into several, if not all, of the distinct cell types present in the chick retina. These data indicate that Otx2 might have a double role in eye development. First, it might be necessary for the early specification and subsequent functioning of the pigment epithelium. Later, OTX2 expression might be involved in retina neurogenesis, defining a differentiation feature common to the distinct retinal cell classes.

Animals↗
PubMed1997

Mapping of a potent transcriptional repression region of the human homeodomain protein EVX1.

The human homeodomain protein EVX1 is a transcriptional repressor in transfected mammalian cells and this function depends on a region carboxyl-terminal to the homeodomain. In this study, we transiently expressed several deletions of the EVX1 C-terminal region in mammalian cells and investigated their effect on the transcription of a reporter gene directed by different promoters. We show that the repressor activity maps to a region of 51 amino acids with a high abundance of alanine and proline residues. This region is able to transfer the repressor function to either the entire HOXC6 or CREB transcription factors, or to the GAL4 DNA binding domain.

3T3 Cells↗
PubMed1997

The human homeodomain protein OTX2 binds to the human tenascin-C promoter and trans-represses its activity in transfected cells.

Homeodomain-containing proteins mediate many transcriptional processes in eukaryotes during development. Recently, mammalian homeodomain proteins involved in the anterior head formation have been discovered, but their effect on gene transcription has never been investigated. Here we report on the ability of the human homeodomain protein OTX2 to bind with high affinity to a target sequence present in the promoter of the gene encoding the human extracellular matrix protein tenascin-C and to repress its transcriptional activity in transiently transfected cells.

Animals↗
PubMed1996

EMX1 homeoprotein is expressed in cell nuclei of the developing cerebral cortex and in the axons of the olfactory sensory neurons.

We analyzed the distribution of EMX1 during mouse development. EMX1 is a homeoprotein encoded by Emx1, a regulatory homeobox gene expressed in the developing forebrain. Its distribution essentially overlaps the expression domains of Emx1 transcripts. The EMX1 protein is present in the developing dorsa telencephalon, that is in the cerebral cortex, olfactory bulb and hippocampus. In the cerebral cortex EMX1 is present in nuclei of proliferating, differentiating and most mature neurons belonging to all cortical layers. In the olfactory bulb it is present in all proliferating cells during development, whereas postnatally it is faintly expressed in some mitral cells. Non-cerebral localizations include a transient expression in branchial pouches, in the apical ectodermal ridge of the developing limbs and in the developing kidney. Of particular interest is the presence of EMX1 in the olfactory nerve from its first appearance during embryogenesis to birth. The protein is present in axons of olfactory sensory neurons along their entire length, including their terminals in spherical regions of neuropil in the olfactory bulb called glomeruli.

Animals↗
PubMed1996

OTX2 homeoprotein in the developing central nervous system and migratory cells of the olfactory area.

We analyzed the distribution of OTX2 during mouse development. OTX2 is a homeoprotein encoded by Otx2, a vertebrate homeobox gene expressed in the developing brain and anterior head regions. The protein is already detectable in pre-streak embryos, in nuclei of embryonic ectoderm or epiblast and primitive endoderm or hypoblast. Its distribution is uniform along the entire epiblast, while showing an antero-posterior gradient along the hypoblast at the time when primitive streak first forms. Between embryonic day 7 (E7) and E7.5 there is a progressive confinement of the protein to the anterior ectoderm corresponding to the forming headfold. At E7.5-E7.8, the protein is mainly confined in this region but is still present, though at lower level, in more posterior ectoderm. Starting from day 8 of development it is essentially confined to anterior neuroectoderm corresponding to presumptive fore- and midbrain. Its subsequent distribution in forebrain, midbrain, developing isthmo-cerebellum and posterior central nervous system is analyzed in detail. Of particular interest is the presence of OTX2 in nuclei of cells of the olfactory system starting from its origin in the olfactory placode. OTX2 protein is present in some cells of the olfactory epithelium, in both the major olfactory epithelium and the vomero-nasal organ, and in scattered migratory cells present in the mesenchyme outside it. These cells surround the axon bundles of the olfactory nerve along its path from the olfactory epithelium in the nasal cavities to the olfactory bulb in rostral telencephalon and include both ensheathing glial cells and luteinizing hormone-releasing hormone (LHRH)-positive cells.

Age Factors↗
PubMed1995

Transcriptional repression by the human homeobox protein EVX1 in transfected mammalian cells.

The human homeobox protein EVX1 (EVX1) is thought to play an important role during embryogenesis. In this study, the effect of EVX1 on gene transcription has been investigated in transfected mammalian cells. EVX1 expression represses transcription of a reporter gene directed by either cell-specific or viral promoter/enhancer sequences in a variety of mammalian cell lines and in a concentration-dependent manner. Transcriptional repression is independent of the presence of DNA-binding sites for EVX1 in all the promoters we tested. Furthermore, repression by EVX1 is evident also using a TATA-less minimal promoter in the reporter construct. A carboxyl-terminal proline/alanine-rich region of EVX1 seems to be responsible for the transcriptional repression activity, as suggested by transfection of EVX1 mutants. We speculate that the repressor function of EVX1 contributes to its proposed role in embryogenesis.

Animals↗
PubMed1994

Ras antagonizes cAMP stimulated glucagon gene transcription in pancreatic islet cell lines.

Ras, a GTP-binding protein, converts membrane tyrosine kinase signalling to changes in gene expression patterns. Utilising a rat glucagon promoter-CAT construct (p[-1.1]GLU-CAT) we demonstrate in transient transfection experiments that the oncogenic Ras inhibits cAMP-dependent activation of p[-1.1]GLU-CAT in both glucagonoma InR1-G9 and insulinoma beta-TC1 cells. Conversely, the expression of a dominant negative mutant of Ras enhances the cAMP-induced activation of p[-1.1]GLU-CAT transcription in these cells. Our data suggests a functional interference of Ras with the cAMP-dependent transcription of the glucagon gene.

Adenoma, Islet Cell↗
PubMed1993

AP-1 activity during normal human keratinocyte differentiation: evidence for a cytosolic modulator of AP-1/DNA binding.

Increased levels of c-fos and c-jun expression have been observed in differentiating epithelial cells. However, no data are available on activator protein 1 (AP-1) activity during keratinocyte differentiation. In this work we investigated c-fos and c-jun gene expression and AP-1-(12-O-tetradecanoylphorbol-13-acetate)-responsive enhancer element (TRE) binding activity during keratinocyte differentiation utilizing both authentic and in culture-reconstituted human epidermis. We demonstrate that: (i) in reconstituted epidermis, non-differentiated and differentiated keratinocytes express equivalent levels of c-Jun, while in reconstituted epidermis permanently grafted onto athymic mice, as well as in authentic epidermis, c-Jun is predominantly expressed in the granular layer of the tissue. Equivalent levels of c-fos expression have been found in all the layers of both reconstituted and authentic epidermis. (ii) Nuclear extracts from cultures enriched in differentiated keratinocytes display an 80-90% reduction of AP-1 activity when compared to extracts from cultures enriched in nondifferentiated cells. (iii) Cytosolic extracts obtained from cultures enriched in differentiated cells reduce, in a concentration-dependent manner, the AP-1 activity present in nuclear extracts of both mammalian and Drosophila cells. (iv) The specific TRE binding activity of a recombinant c-Jun protein is significantly reduced by cytosolic extracts of differentiated keratinocytes, while the specific DNA binding of the purified recombinant human homeoprotein HOX4B is not. (v) The dephosphorylation, by alkaline phosphatase, of cytosolic extracts increases the inhibitory activity already present or makes evident a latent activity.

Animals↗
PubMed1993

The homeotic gene products in the control of cell differentiation and proliferation.

Embryo development is controlled by a successive series of genes that provide each cell in the growing embryo with precise position information. Knowledge of these genes is known most completely from Drosophila, where a simple initial pattern generated by maternal effect genes is gradually segmented by the sequential transient expression of three successive series of genes: the gap genes, the pair-rule genes, and the segment polarity genes. Superimposing their action on the preexisting segments, these homeotic genes cause unique and often very distinctive patterns of differentiation for different segments. In humans, about 40 homeotic genes have been identified and are grouped into four clusters on chromosomes 2, 7, 12, and 17, whose organization reflects their spatial and temporal expression. Several homeotic genes have been found expressed not only in embryonic tissues, but also in adult tissues, most notably in the hematopoietic lineage, and also in tumors, especially leukemia, teratocarcinoma, and neuroblastoma, wherein their expression pattern is modified in a complex manner by retinoic acid. The target genes of the transcription factors encoded by the homeotic genes are largely unknown, but recent reports indicate that they may regulate the expression of adhesion molecules on the membrane and the production of components of the extracellular matrix. Abnormal expression of these genes can therefore affect not only cell proliferation, but also the spread of cells to aberrant locations.

Animals↗