Biomedical subjects

A Simeone

Publications and source records attributed to A Simeone.

At least 73 records · Page 4Linked to original sources

PubMed1995

The proto-oncogene RON is involved in development of epithelial, bone and neuro-endocrine tissues.

We previously showed that the proto-oncogene RON encodes the tyrosine kinase receptor for Macrophage Stimulating Protein (MSP), originally isolated as a chemotactic factor for peritoneal macrophages. To elucidate the biological role of MSP we studied the expression of the Ron receptor in vivo, and the response to the factor in vitro. RON specific transcripts were detectable in mouse liver from early embryonal life (day 12.5 p.c.) through adult life. Adrenal gland, spinal ganglia, skin, lung and--unexpectedly--ossification centers of developing mandible, clavicle and ribs were also positive at later stages (day 13.5-16.5 p.c.). From day 17.5 RON was expressed in the gut epithelium and in a specific area of the central nervous system, corresponding to the nucleus of the hypoglossus. In adult mouse tissues RON transcripts were observed in brain, adrenal glands, gastro-intestinal tract, testis and kidney. Epithelial, osteoclast-like and neuroendocrine cells express the Ron receptor and respond to MSP in vitro. In the neuroendocrine PC12 cell line, while NGF induced growth arrest and morphological differentiation, MSP behaved as a strong mitogen. These findings show that the Ron receptor and its ligand are involved in the development of epithelial tissues, bones, and neuroendocrine derivatives driving cells towards the proliferation program.

Animals↗

PubMed1995

Expression of the receptor tyrosine kinase substrate genes eps8 and eps15 during mouse development.

Receptor tyrosine kinases (RTKs) control proliferation and differentiation through their ability to bind and/or phosphorylate intracellular substrates. The repertoire of substrates recruited by different RTK is largely overlapping. It is not clear, therefore, how a cell distinguishes among signals originating from different RTKs. One possibility is that selective availability of substrates participates in the regulation of this process. To gain insight into this issue, we studied the expression pattern, during mouse embryogenesis, of the eps8 and eps15 genes, which encode two recently identified RTK substrates. Both genes are expressed from E 10 in a restricted fashion. eps8 is first expressed in frontonasal neural crest-derived cells, in the mesenchyme of branchial arches and in the liver primordium. At E 12.5-E 14, eps8 is additionally expressed in the central nervous system (CNS) in a regional restricted pattern at the met-mesencephalic transition area and in the developing submandibular salivary glands. eps15 is expressed at E 10 in the liver primordium, in the spinal ganglia and in the encephalic ganglia derived from the hindbrain neural crest. In addition, at E 12.5-E 14, eps15 is expressed, along all the CNS, in the ventricular zone where undifferentiated neuroblasts are located. The regional pattern of developmental expression of these two substrates sharply contrasts with their ubiquitous expression in adults, raising the possibility that their expression during embryogenesis is linked to selective proliferative and/or differentiative responses of specific neuroectodermal regions and body organs.

Adaptor Proteins, Signal Transducing↗

PubMed1995

Expression of runt in the mouse embryo.

The Drosophila runt locus controls early events in embryogenesis. A human homologue (CBFA2) was originally identified because of its involvement in the t(8;21) associated with a subtype of acute myeloid leukaemia. The phylogenetically conserved region (runt box) was reported to correspond to a DNA binding domain. In order to investigate whether runt also plays a role in mammalian development, we have conducted a preliminary survey of its expression in the mouse embryo. Expression in embryonic tissues was detected starting from day 9.2 post coitum. From day 10.5 post coitum, highest levels are found in the neural tube, sensory ganglia, specialised sensory epithelial structures (olfactory and gustatory mucosa, follicles of the vibrissae), all chondrogenic centres (both of neural crest and of mesodermal origin), and the genital system (the gonad, the paramesonephros, and the genital tubercle). Unambiguous expression in the haemopoietic system could be established for the thymus. The data suggest a pleiotropic role for mammalian runt in embryogenesis.

Animals↗

PubMed1995

Retinoic acid induces stage-specific antero-posterior transformation of rostral central nervous system.

We report a time-course analysis of the effect of retinoic acid (RA) on the development of the mouse central nervous system (CNS) from the beginning of gastrulation throughout induction and patterning of the neural tube. RA administration induces three different, stage-specific alterations of brain development, indicating perturbation of different morphogenetic steps during the establishment of a neural pattern. In particular, treatment at mid-late streak stage (7.2-7.4 days post coitum (d.p.c.)) results in early repression of Otx2 expression in the posterior neuroectoderm of the head fold and in the ventral mid line, including the prechordal plate and the rostralmost endoderm, followed by loss of forebrain morphological and molecular identities, as revealed by analysis of the expression of regionally-restricted brain genes (Otx2, Otx1, Emx2, Emx1 and Dlx1). In these embryos, reduction of the Otx2 expression domain correlates with hindbrain expansion marked by rostral extension of the Hoxb-1 expression domain. Our analysis indicates that RA interferes with the correct definition of both planar and vertical morphogenetic signals at specific developmental stages by affecting gene expression in the regions which are likely either to produce or to respond to these signals. We suggest that retinoids may contribute to early definition of head from trunk structures by selecting different sets of regulatory genes.

Animals↗

PubMed1995

Forebrain and midbrain regions are deleted in Otx2-/- mutants due to a defective anterior neuroectoderm specification during gastrulation.

We have replaced part of the mouse homeogene Otx2 coding region with the E. coli lacZ coding sequence, thus creating a null allele of Otx2. By 9.5 dpc, homozygous mutant embryos are characterized by the absence of forebrain and midbrain regions. From the early to midstreak stages, endomesodermal cells expressing lacZ fail to be properly localized anteriorly. In the ectodermal layer, lacZ transcription is progressively extinguished, being barely detectable by the late streak stage. These data suggest that Otx2 expression in endomesoderm and ectoderm is required for anterior neuroectoderm specification. In gastrulating heterozygous embryos, a post-transcriptional repression acts on lacZ transcripts in the ectoderm, but not in the external layer, suggesting that different post-transcriptional mechanisms control Otx2 expression in both layers.

Animals↗

PubMed1995

Developmental analysis of murine Promyelocyte Leukemia Zinc Finger (PLZF) gene expression: implications for the neuromeric model of the forebrain organization.

Promyelocyte Leukemia Zinc Finger (PLZF) is a Kruppel-like zinc finger gene previously identified in a unique case of acute promyelocytic leukemia (APL) as the counterpart of a reciprocal chromosomal translocation involving the retinoic acid receptor alpha gene (RAR alpha). PLZF is highly conserved throughout evolution from yeast to mammals. To elucidate its role, we isolated the murine PLZF gene and studied its expression during embryogenesis. PLZF is expressed in an extremely dynamic pattern with transcripts appearing at E 7.5 in the anterior neuroepithelium and quickly spreading to the entire neuroectoderm until E 10. At E 8.5, PLZF is transcribed in most of the endoderm. During mid to late gestation PLZF is expressed in restricted domains of the developing CNS as well as in specific organs and body structures. We have focused our attention on the developing forebrain where PLZF is transcribed in a transverse, segment-like domain corresponding to the anterior pretectum, in the alarmost part of the dorsal thalamus, in the epithalamus, and in the hypothalamus along a defined longitudinal subdomain. Furthermore, PLZF is expressed in several segmentary boundaries, among them, the zona limitans intrathalamica. Combined analysis with other regionally restricted genes, such as Orthopedia and Dlx1, indicates that in the hypothalamus the PLZF domain is contained within that of Orthopedia and both are complementary to that of Dlx1. Our data suggest a role for PLZF in the establishment and maintenance of transverse identities, longitudinal subdomains, and interneuromeric boundaries, providing additional evidences in favor of the neuromeric organization of the forebrain.

Animals↗

PubMed1995

Fibroblast growth factor 2 increases Otx2 expression in precursor cells from mammalian telencephalon.

Dissociated primary cultures from rat telencephalon at different developmental stages were used to study the effect of basic fibroblast growth factor (FGF2) on Otx2, Dlx1, and Emx1, three homeobox genes expressed in different regions of the developing mammalian forebrain. At embryonic day (E)13.5. the regional pattern of expression of Otx1, Otx2, Dlx1, Dlx2, Dlx5, and Emx1 is maintained in primary culture, suggesting that cells are already committed to a regional identity at this stage. In these cultures, Otx2 is expressed by precursor cells, whereas Dlx1 and Emx1 are predominantly expressed by postmitotic cells. We found that FGF2 increased Otx2 expression within precursor cells and the total number of Otx2-expressing cells. This effect was gene-specific, dose-dependent, and temporally regulated, with larger effects at earlier stages of development (E11.5). At E13.5, the effect of FGF2 on Otx2 expression was restricted to the basal telencephalon. Our results suggest that a restricted population of neuroblasts respond to FGF2 in a temporally regulated fashion by proliferating and increasing Otx2 expression. This interaction between FGF2 and Otx2 may be important for the regulation of neurogenesis in the forebrain.

Animals↗

PubMed1995

Expression pattern of two otx genes suggests a role in specifying anterior body structures in zebrafish.

We isolated two zebrafish sequences containing a homeobox related to orthodenticle (otd), a gene expressed in the developing head of Drosophila. One of these is clearly homologous to Otx1, a homeobox gene previously reported to be expressed in the developing rostral brain of the mouse. We termed this zebrafish gene otx1. The second gene is not as closely related to Otx1 and is equally divergent from Otx2, a second homeobox gene expressed in the developing rostral brain of the mouse. We termed it otx3, even if a corresponding murine Otx3 gene has not been reported yet. Both genes are expressed in early-gastrula zebrafish embryos in the involuting presumptive anterior mesendoderm. With the extension of the body axis, the expression domain of both genes extends to neuroectodermal regions fated to become fore- and mid-brain. From this stage the expression domains of the two genes differ slightly from each other but both cover the rostral brain with a sharp posterior boundary coinciding with that between midbrain and hind-brain. This late expression closely corresponds to that of the murine Otx1 gene, whereas the earliest expression of both zebrafish otx genes is different from that of Otx1 and reminiscent of that of Otx2 in the mouse. In this light, the zebrafish otx1 and otx3 genes appear to share some expression features of both murine Otx1 and Otx2. It will be of considerable interest to study the specific role of the various genes of the otx family in the development of the zebrafish brain regions. The peculiar spatio-temporal pattern of these genes during early zebrafish gastrulation suggests a role of this gene family in interactions between anterior mesendoderm and neuroectoderm.

Amino Acid Sequence↗

PubMed1994

Chromosome locations of human EMX and OTX genes.

We have determined the chromosomal localization of four human homeobox-containing genes, EMX1, EMX2, OTX1, and OTX2, related to Drosophila genes expressed in the developing head of the fly. Murine homologs of these genes are expressed in specific nested domains in the developing rostral brain of midgestation embryos. DNAs from a panel of 19 rodent-human hybrids, each carrying one or a few human chromosomes such that most human chromosome regions were represented, were tested for the presence of the four gene loci by filter hybridization to radiolabeled probes. Regional chromosomal localization was determined by similarly testing DNAs from hybrid mapping panels for each of the candidate chromosomes. Finally, fluorescence in situ hybridization of cosmid clones for these loci refined the locations, two of which were in the vicinity of previously mapped orphan homeobox genes and two of which were near each other. OTX2, the earliest and most widely expressed gene, maps to chromosome region 14q21-q22; the OTX1 locus maps to 2p13; EMX2 maps to 10q26.1; and EMX1, the most narrowly and lately expressed, maps to 2p14-p13. Thus, these homeobox-containing genes involved in brain development are not linked to any of the four HOX clusters on 7p15-p14, 17q21-q22, 12q12-q13, and 2q31. However, the OTX1 and EMX1 loci may be closely linked on or near 2p13, prompting speculation that a clustered gene structure could have functional significance, as is presumably the case for the HOX clusters.

Animals↗

PubMed1994

Cloning and characterization of two members of the vertebrate Dlx gene family.

A number of vertebrate genes of the Dlx gene family have been cloned in mouse, frog, and zebrafish. These genes contain a homeobox related to that of Distalless, a gene expressed in the developing head and limbs of Drosophila embryos. We cloned and studied the expression of two members of this family, which we named Dlx5 and Dlx6, in human and mouse. The two human genes, DLX5 and DLX6, are closely linked in an inverted convergent configuration in a region of chromosome 7, at 7q22. Similarly, the two human genes DLX1 and DLX2 are closely linked in a convergent configuration at 2q32, near the HOXD (previously HOX4) locus. In situ hybridization experiments in mouse embryos revealed expression of Dlx5 and Dlx6 mRNA in restricted regions of ventral diencephalon and basal telencephalon, with a distribution very similar to that reported for Dlx1 and Dlx2 mRNA. A surprising feature of Dlx5 and Dlx6 is that they are also expressed in all skeletal structures of midgestation embryos after the first cartilage formation. The expression pattern of these genes, together with their chromosome localization, may provide useful cues for the study of congenital disorders in which there is a combination of craniofacial and limb defects.

Amino Acid Sequence↗

PubMed1994

Orthopedia, a novel homeobox-containing gene expressed in the developing CNS of both mouse and Drosophila.

A novel homeobox-containing gene has been identified. Its name, Orthopedia (Otp), exemplifies the homology shared by both the orthodenticle and Antennapedia homeodomains. Otp is highly conserved in evolution. In mouse, Otp is expressed only in restricted domains of the developing forebrain, hindbrain, and spinal cord. In Drosophila, otp first appears at gastrulation in the ectodermal proctodeum and later in the hindgut, anal plate, and along the CNS. Here, we compare the Otp-, Distal-less homeobox 1-(DIx1-), Orthodenticle homolog 1-(Otx1-), Otx2-, and Empty spiracles homolog 2-expressing domains. Our results indicate that Otp is expressed along the CNS both in mouse and Drosophila; Otp could specify regional identities in the development of the forebrain and spinal cord; transcription of Otp and DIx1 takes place in alternating hypothalamic regions reminiscent of a segment-like pattern; and the structural and functional conservation could correspond to a conserved function maintained in evolution.

Amino Acid Sequence↗

PubMed1994

Hepatocyte growth factor induces proliferation and differentiation of multipotent and erythroid hemopoietic progenitors.

Hepatocyte growth factor (HGF) is a mesenchymal derived growth factor known to induce proliferation and "scattering" of epithelial and endothelial cells. Its receptor is the tyrosine kinase encoded by the c-MET protooncogene. Here we show that highly purified recombinant HGF stimulates hemopoietic progenitors to form colonies in vitro. In the presence of erythropoietin, picomolar concentrations of HGF induced the formation of erythroid burst-forming unit colonies from CD34-positive cells purified from human bone marrow, peripheral blood, or umbilical cord blood. The growth stimulatory activity was restricted to the erythroid lineage. HGF also stimulated the formation of multipotent CFU-GEMM colonies. This effect is synergized by stem cell factor, the ligand of the tyrosine kinase receptor encoded by the c-KIT protooncogene, which is active on early hemopoietic progenitors. By flow cytometry analysis, the receptor for HGF was found to be expressed on the cell surface in a fraction of CD34+ progenitors. Moreover, in situ hybridization experiments showed that HGF receptor mRNA is highly expressed in embryonic erythroid cells (megaloblasts). HGF mRNA was also found to be produced in the embryonal liver. These data show that HGF plays a direct role in the control of proliferation and differentiation of erythroid progenitors, and they suggest that it may be one of the long-sought mediators of paracrine interactions between stromal and hemopoietic cells within the hemopoietic microenvironment.

Animals↗

PubMed1994

Expression of the neuron-specific FE65 gene marks the development of embryo ganglionic derivatives.

The major transcript of the FE65 gene is a neuron-specific mRNA that encodes a nuclear protein whose aminoterminal domain strongly activates the transcription of a reporter gene when fused to a heterologous DNA-binding domain. FE65 gene expression is regulated during neuronal differentiation of the NTERA-2 cell line, and it is temporally and spatially restricted during mouse embryo development. It is first detected around day 10 of gestation in the basal plate of the neural tube, and then, at the subsequent stages of development and in the newborn animals, it is found solely in neural structures. Its expression is most abundant in the neural crest derivatives (e.g. spinal and encephalic ganglia), ganglionic structures of sense organs (ganglionic layer of the retina and olfactory epithelium), as well as the ganglionic structures of the autonomic nervous system. Thus FE65 gene expression can be considered a marker of the development of embryo ganglionic derivatives.

Animals↗

PubMed1994

Developmental expression of the RET protooncogene.

The RET protooncogene encodes a transmembrane protein of the receptor-type tyrosine kinase family whose ligand has not yet been identified. Its activation in vivo is restricted to human carcinomas of the thyroid. In order to learn more about the possible role played by RET during normal development, we have examined its expression by performing in situ hybridization experiments on mouse embryos. Here, we show that the RET protooncogene is expressed during mouse embryogenesis in an unusual temporal and spatial manner. In fact, its expression was first detected around day 10 of gestation in the basal plate of the neural tube and in the developing encephalic ganglia, and later its pattern of expression was definitely established in neural structures, mostly in neural crest derivatives (spinal and encephalic ganglia). As far as the central nervous system is concerned, RET expression was confined to the ventral part of the midbrain from 12.5 days postcoitum (dpc) until birth. RET was also found to be expressed within structures of sensory organs such as the ganglial layer of the retina and the olfactory epithelium. A peculiar pattern of RET expression was clearly observed in the wall of the gut and in the nephrogenic zone of the developing kidney cortex, specifically in the metanephrogenic vesicles. Finally, RET was found to be expressed in the liver mostly between 12.5 dpc and 14.5 dpc. In conclusion, its expression in the early stages of embryogenesis suggests that RET may play a role in the differentiation of specific neural structures and the excretory system.

Animals↗

PubMed1993

A vertebrate gene related to orthodenticle contains a homeodomain of the bicoid class and demarcates anterior neuroectoderm in the gastrulating mouse embryo.

We studied the expression of two vertebrate homeobox genes, Otx1 and Otx2, related to orthodenticle, a gene expressed in the developing head of Drosophila. Both genes are expressed in restricted regions of the developing rostral brain including the presumptive cerebral cortex and olfactory bulbs. The expression patterns of the two genes in diencephalon suggest that they both have a role in establishing the boundary between presumptive dorsal and ventral thalamus. They are also expressed in regions of the developing olfactory, auricolar and ocular system, including the covering of the optic nerve. Otx1 expression is detectable from day 8 of gestation in telencephalic, diencephalic and mesencephalic regions. From day 10.5 of gestation its expression extends to some metencephalic areas. Otx2 appears to be already expressed in the epiblast of prestreak embryos. It persists in the entire embryonic ectoderm for some time after the onset of gastrulation. In midstreak embryos its expression appears progressively restricted to the anterior embryonic ectoderm corresponding to presumptive fore- and mid-brain. In early midgestation embryos it is expressed in telencephalic, diencephalic and mesencephalic regions but from day 11.75 of gestation its expression disappears from dorsal telencephalon and is confined to diencephalic and mesencephalic regions. Otx2 is one of the earliest genes expressed in the epiblast and immediately afterwards is expressed in anterior neuroectoderm, demarcating rostral brain regions even before headfold formation. Its gene product contains a homeodomain of the bicoid class and is able to recognize and transactivate a bicoid target sequence.

Amino Acid Sequence↗

PubMed1993

The murine cripto gene: expression during mesoderm induction and early heart morphogenesis.

The murine cripto gene encodes a 171-aminoacid epidermal growth factor-related protein, with 93% similarity to its human counterpart in the 'EGF-like' domain. The murine cripto mRNA contains two B1 repeats in its 3' non-coding region and a 163-nucleotide homology to the human mRNA. The mouse cripto gene is expressed at low level in specific organs of the adult animal such as spleen, heart, lung and brain. In situ hybridization analysis during murine embryogenesis (day 6.2 to day 10.5) reveals a very restricted expression pattern. cripto transcripts are first detected in a few epiblastic cells at day 6.5. During gastrulation, the transcripts are expressed in the forming mesoderm and later during development cripto gene expression is restricted to the truncus arteriosus of the developing heart. This expression pattern suggests a role for cripto gene in the determination of the epiblastic cells that subsequently give rise to the mesoderm.

Amino Acid Sequence↗

PubMed1993

Homeobox genes in the developing central nervous system.

A number of genes containing sequences coding for DNA-binding domains homologues to homeobox sequences in Drosophila have been isolated in vertebrate and their mechanism of action have been studied. In Particular Hox family genes share with Drosophila homeotic genes a genomic organization in gene clusters and an expression pattern that is similar in a number of important respects. In situ hybridization experiment have shown that there is a strict correspondence, or colinearity, between the order of the Hox genes (3' to 5') within the chromosomal cluster and that of their expression domains (anterior to posterior) in the embryo. Recent data obtained in embryonal carcinoma (EC) cells induced to differentiate by retinoic acid (RA) cast some light on the molecular mechanisms underlying the colinear expression of the Hox genes.

Amino Acid Sequence↗

PubMed1992

Differential DNA binding properties of three human homeodomain proteins.

The products of three human homeobox containing (HOX) genes, 2C, 3C and 4B, were produced in insect cells using the Baculovirus expression system and purified to near homogeneity. In this system we observed that the DNA binding forms of the three proteins are not glycosylated. HOX 3C and 4B are phosphorylated in insect cells, while HOX 2C is not. The three HOX proteins bind to a DNA sequence known to be a target site for Antennapedia protein with a very similar affinity (Kd = 1-2 x 10(-9) M). We then measured their binding properties to four human sequences present in the HOX 3D, 4C, 1C and 4B promoters. Two of these sequences have been reported to be binding sites for HOX proteins. HOX 2C, 3C and 4B behaved quite differently, showing low affinity for promoters of genes located upstream from their own gene in the HOX clusters and a higher affinity for regulatory sequences of their own gene and downstream HOX genes.

Animals↗