Immortalization of neuroendocrine pinealocytes from transgenic mice by targeted tumorigenesis using the tryptophan hydroxylase promoter

Tryptophan hydroxylase (TPH) is the first enzyme in both serotonin and melatonin biosynthesis in neuroendocrine cells of the pineal gland. The lack of immortalized neuroendocrine pineal cell lines has been a major obstacle to the study of the tissue-specific and circadian regulation of TPH gene expression in the pineal gland. Previously, we demonstrated that a 6.1 kb 5' upstream region of the mouse TPH gene directs the restricted expression of a lacZ reporter gene to the pineal gland and the raphe nuclei of transgenic mice. Therefore, to develop TPH-expressing pineal cell lines we first established transgenic mice carrying a construct consisting of 6.1 kb of 5' flanking region fused to the SV40 T-antigen. These animals developed highly invasive pineal tumors and died at 12-15 weeks of age. The pineal tumors obtained from the transgenic mice were utilized to establish the immortalized pinealocyte-derived cell lines. These cells express two marker enzymes, TPH and serotonin N-acetyltransferase (NAT). In pineal gland TPH and NAT expressions have been known to be regulated during circadian cycle. The two established cell lines therefore promise to be a valuable in vitro model system for the study of the rhythmic nature of the pineal function at molecular level in mammal.     

Cruciform-extruding regulatory element controls cell-specific activity of the tyrosine hydroxylase gene promoter

Tyrosine hydroxylase (TH) is expressed specifically in catecholaminergic cells. We have identified a novel regulatory sequence in the upstream region of the bovine TH gene promoter formed by a dyad symmetry element (DSE1;-352/-307 bp). DSE1 supports TH promoter activity in TH-expressing bovine adrenal medulla chromaffin (BAMC) cells and inhibits promoter activity in non-expressing TE671 cells. DNase I footprinting of relaxed TH promoter DNA showed weak binding of nuclear BAMC cell proteins to a short sequence in the right DSE1 arm. In BAMC cells, deletion of the right arm markedly reduced the expression of luciferase from the TH promoter. However, deletion of the left DSE1 arm or its reversed orientation (RevL) also inactivated the TH promoter. In supercoiled TH promoter, DSE1 assumes a cruciform-like conformation i.e., it binds cruciform-specific 2D3 antibody, and S1 nuclease-cleavage and OsO4-modification assays have identified an imperfect cruciform extruded by the DSE1. DNase I footprinting of supercoiled plasmid showed that cruciformed DSE1 is targeted by nuclear proteins more efficiently than the linear duplex isomer and that the protected site encompasses the left arm and center of DSE1. Our results suggest that the disruption of intrastrand base-pairing preventing cruciform formation and protein binding to DSE1 is responsible for its inactivation in DSE1 mutants. DSE1 cruciform may act as a target site for activator (BAMC cells) and repressor (TE671) proteins. Its extrusion emerges as a novel mechanism that controls cell-specific promoter activity.     

Regulation of tyrosine hydroxylase and aromatic L-amino acid decarboxylase by dopaminergic drugs

We provide evidence that dopamine receptors differentially modulate tyrosine hydroxylase and aromatic L-amino acid decarboxylase in the mouse striatum. The dopamine D1 receptor family (D1-like) antagonist, R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1 H-3-benazepine (SCH 23390), elevated aromatic L-amino acid decarboxylase activity and protein content in striatum, as well as the mRNA for the enzyme in midbrain. The dopamine D1-like receptor agonist, (+/-)-1-phenyl-2,3,4,5-tetrahydro-(1 H)-3-benzazepine-7,8-diol (SKF 38393), had no effect on aromatic L-amino acid decarboxylase. The dopamine D1-like drugs had no effect on tyrosine hydroxylase. In contrast, the dopamine D2 receptor family (D2-like) antagonists haloperidol and spiperone elevated both tyrosine hydroxylase and aromatic L-amino acid decarboxylase activities. The increase in aromatic L-amino acid decarboxylase activity was accompanied by elevated enzyme protein content but not mRNA. The dopamine D2-like receptor agonists, bromocriptine, quinpirole and (+/-)-7-hydroxydipropylaminotetralin (7-OH-DPAT), all decreased striatal tyrosine hydroxylase. Under the conditions used, bromocriptine and 7-OH-DPAT, but not quinpirole, decreased aromatic L-amino acid decarboxylase activity of striatum. Both the dopamine D1- and D2-like receptor antagonists enhanced the turnover of striatal dopamine to differing degrees, as judged by the ratio of acid metabolites of dopamine to dopamine. Taken together our results indicate that aromatic L-amino acid decarboxylase can be modulated independently of tyrosine hydroxylase.     

Reduced striatal tyrosine hydroxylase activity is not accompanied by change in responsiveness of dopaminergic receptors following chronic treatment with deprenyl

Deprenyl is the only selective monoamine oxidase B (MAO-B) inhibitor that is in clinical use for the treatment of Parkinson's disease. Our previous studies showed that chronic treatment of rats with low (MAO-B selective) doses of deprenyl inhibited dopamine (DA) re-uptake and enhanced DA release in the striatum. These changes could affect DA synthesis rate by activation of negative feedback loops. Chronic deprenyl treatment has also been suggested to cause down-regulation of release-modulating DA receptors. The effects of chronic and acute treatment with deprenyl on ex vivo striatal tyrosine hydroxylase activity were therefore studied, by determination of steady-state tissue level of DOPA following administration of NSD-1015 (100 mg/kg i.p.). In addition, we assessed changes in the in vivo sensitivity of dopaminergic receptors from the reduction in DOPA extracellular level after systemic apomorphine administration (2.5 mg/kg s.c.), following elevation of microdialysate DOPA by systemic or local aromatic amino acid decarboxylase inhibition with NSD-1015. Chronic treatment with deprenyl (0.25 mg/kg s.c. daily for 21 days) caused a significant reduction in tyrosine hydroxylase activity to 60% of control, with no change in the apomorphine-induced reduction of microdialysate DOPA and DOPAC. The reduction in tyrosine hydroxylase activity is compatible with our previous results showing an increase in striatal DA extracellular level following chronic treatment with deprenyl. The increased extracellular striatal DA level could reduce tyrosine hydroxylase activity through activation of a negative feedback loop, by activation of either presynaptic or postsynaptic DA receptors.     

Expression of rat bone sialoprotein promoter in transgenic mice

Bone sialoprotein (BSP) is a major protein of the mineralized bone extracellular matrix that has been implicated in the nucleation of hydroxyapatite crystals. Our previous studies have demonstrated that BSP mRNA is expressed by differentiated osteoblasts, odontoblasts, and cementoblasts involved in de novo mineralized tissue formation in a tissue-specific and developmentally regulated manner. To determine the basis of the selective expression of the BSP gene, we have generated four transgenic mouse lines in which 2.7 kb of the rat BSP promoter ligated to a luciferase reporter gene has been stably integrated into the mouse genome. Assays of luciferase activities in 5-day-old animals has revealed consistently high levels in bone tissues with negligible activities in various other organs including kidney, liver, stomach, intestine, and spleen. In some animals, variable expression was observed in brain and skin. Temporal analyses revealed the highest luciferase expression in neonatal bones, with expression decreasing markedly with subsequent growth and development, as observed previously for the endogenous gene in rats. Immunohistochemical analysis of luciferase activity and in situ hybridization of luciferase mRNA in bone tissues show that differentiated osteoblasts express the highest levels of luciferase, consistent with the induction of endogenous gene expression. These studies demonstrate that the regulation of the BSP gene during osteoblastic differentiation, together with its tissue-specific, developmentally regulated expression, is primarily mediated within the 2.7 kb region of the promoter.     

Analysis of the human ferrochelatase promoter in transgenic mice

Ferrochelatase catalyzes the chelation of ferrous iron and protoporphyrin to form heme. It is expressed as a housekeeping gene in all cells, but is upregulated during erythropoiesis. Ferrochelatase activity is deficient in the inherited disease protoporphyria as a result of heterogeneous mutations. Although human ferrochelatase is transcribed from a single promoter in both nonerythroid and erythroid cells, previous studies using transient transfection assays failed to demonstrate erythroid-specific increased expression from 4.0 kb of the human ferrochelatase promoter containing the erythroid cis-elements, GATA and NF-E2. The present study analyzes the in vivo regulation of the ferrochelatase gene to provide insights into the mechanism of its erythroid-specific enhancement. Transgenic (TG) mouse lines were generated in which the luciferase reporter gene was driven by either a 150-bp ferrochelatase minimal promoter (-0.15 TG) or by a 4.0 kb extended 5' upstream region (-4.0 TG). Expression of the -4.0 TG transgene was generally consistent with the endogenous gene during embryonic development and in nonerythroid and erythroid tissues as demonstrated by Northern blotting and mRNA in situ hybridization. The -4.0 TG was expressed at a higher level than the -0.15 TG in nonerythroid and erythroid tissues, including during extramedullary erythropoiesis induced by n-acetylphenylhydrazine injection. The enhanced erythroid expression of the -4.0 TG correlates with the appearance of a DNase I hypersensitive site in the 5' flanking region of the transgene. Therefore, in the context of chromosomal integration, the 5' flanking region of the ferrochelatase gene is necessary and sufficient to confer high levels of transgene expression in erythroid tissue.     

Regulation of tyrosine hydroxylase mRNA stability by protein-binding, pyrimidine-rich sequence in the 3'-untranslated region

The stability of mRNA for tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine synthesis, is regulated by oxygen tension in the pheochromocytoma-derived PC12 cell line. We previously identified a pyrimidine-rich 27-base-long protein-binding sequence in the 3'-untranslated region of TH mRNA that is associated with hypoxia-inducible formation of a ribonucleoprotein complex (hypoxia-inducible protein-binding site (HIPBS)). In this study, we show that HIPBS is an mRNA stabilizing element necessary for both constitutive and hypoxia-regulated stability of TH mRNA. The mutations within this sequence that abolish protein binding markedly decrease constitutive TH mRNA stability and ablate its hypoxic regulation. A short fragment of TH mRNA that contains the wild-type HIPBS confers the increased mRNA stability to the reporter chloramphenicol acetyltransferase mRNA. However, it is not sufficient to confer hypoxic regulation. The HIPBS element binds two isoforms of a 40-kDa poly(C)-binding protein (PCBP). Hypoxia induces expression of the isoform 1, PCBP1, but not the isoform 2, PCBP2, in PC12 cells.     

Analysis of kafirin promoter activity in transgenic tobacco seeds

Sequences corresponding to 855 bp of 5' promoter region and the transit peptide from lambdaGK.1,a genomic clone encoding a 22 kDa alpha-kafirin seed protein from sorghum, were translationally fused to a cloned beta-glucuronidase (GUS) coding sequence from uidA and transferred to tobacco via Agrobacterium tumefaciens-mediated transformation. No GUS expression was detectable at any stage of growth in stems or leaves of these plants. However, GUS expression was detected in both embryo and endosperm tissues of resulting tobacco seeds 10-15 days after flowering. Dissected tissues indicate endosperm expression was localized within the bulk endosperm and not within the parenchyma cell layer underlying the integument. These studies also demonstrate that within dissected tobacco embryos, expression from the kafirin promoter was restricted to the mesocotyl region.     

Regulation of human erythropoietin gene induction by upstream flanking sequences in transgenic mice

Human erythropoietin (Epo) gene expression is inducible by hypoxia or anaemia in the kidney and liver. Previous transgenic mouse experiments have demonstrated that sequences required for Epo gene induction in the kidney reside in a 7 8 kb Barn HI fragment located 6 kb upstream of the gene. To sublocalize these sequences, we performed Desoxyribonuclease I (DNAse I) mapping studies using transgenic mice which carried this DNA fragment. These studies revealed a DNAse I hypersensitive site (DNAse I HS) located 4 6 kb from the upstream end of the 7.8 kb fragment in anaemic kidney and liver samples. Sequence analysis of the region encompassing the DNAse I HS revealed an element with remarkable homology to the 3' Epo gene hypoxia-inducible enhancer. This suggested the presence of an additional regulatory element that contributes to the control of hypoxia-inducible Epo gene expression in kidney and liver. We constructed transgenic mice containing the human Epo gene linked to either the 5 kb upstream or 2.5 kb downstream portion of the 7.8kb fragment. Inducible expression was limited to the liver. Thus, neither fragment was alone sufficient to confer kidney inducible expression. These findings indicate that sequences more than 8.5 kb upstream of the Epo gene are required for kidney-specific induction. They suggest that either those sequences reside in an 0.3 kb Hind III fragment located between the 5 kb and the 2.5 kb fragments or that sequences in the 5 kb or 0.3 kb fragments must interact with sequences in the 2.5 kb fragment to allow Epo gene induction in the kidney.     

Increased site-specific phosphorylation of tyrosine hydroxylase accompanies stimulation of enzymatic activity induced by cessation of dopamine neuronal activity

The growth of ferret preimplantation blastocysts in vivo, collected between 156 and 240 hr post coitum, was investigated. A technique, combining immunosurgery and differential fluorochrome staining, was used to discriminate between inner cell mass (ICM) and trophectoderm (TE) cells. Using the stains propidium iodide and bisbenzimide (Hoechst 33342), the ICM was stained blue and the TE was stained pink. The ICM and TE counts for 90 blastocysts, respectively, averaged 25 and 63 at 156 hr and increased exponentially to 2077 and 4137 at 240 hr. The Box-Cox procedure was used for choosing a transformation that minimized the error sum of squares for a linear regression of Y (cell count) on X (time in hr). Logarithmic transformations of the ICM, TE and total cell count gave a good fit, but the following equations obtained by the Box-Cox procedure provided the best fit, where Y is cell count and X is time in hours. For inner cell mass: Y = [(176.06 + 2.45X)/-899.44 + 1]-3.33; trophectoderm: Y = [(301.38 + 14.48X)/-6863.42 + 1]-10; and total: Y = [(2266.97 + 17.0X)/-7837.21 + 1]-5. The R2 values were 0.73, 0.84, and 0.84, respectively. The exponential growth of the ferret embryo during the time interval that measurements were made fits the general pattern described for other mammalian embryos. This report is the first to characterize the pattern of cell allocation and growth in preimplantation blastocysts of the ferret, and the first such report for a carnivore. The pattern of in vivo development provides a standard for judging the quality of in vitro produced and matured ferret embryos and, concomitantly, a means to evaluate culture systems.     

Temporal and spatial specificity of PDGF alpha receptor promoter in transgenic mice

Aberrant expression of the platelet-derived growth factor alpha receptor (PDGF alpha R) has been linked to developmental abnormalities in vertebrate models, and has been implicated in multiple disease states in humans. To identify cis-acting regulatory elements that dictate expression of this receptor, we generated transgenic mice bearing the reporter gene beta-galactosidase (lacZ) under the control of a 6-kb promoter sequence. Expression of lacZ was monitored throughout embryonic development, with special focus on nervous tissue, skeleton, and several organ systems wherein PDGF alpha R expression is thought to play a pivotal role. In several independent transgenic mouse strains, lacZ expression recapitulated predominant features of PDGF alpha R gene expression during mouse development. These results demonstrate that critical tissue-specific regulatory elements for PDGF alpha R expression are located within a 6-kb upstream region of the PDGF alpha R gene.     

Parathyroid hormone represses alpha 1(I) collagen promoter activity in cultured calvariae from neonatal transgenic mice

We examined the effect of PTH on the activity of alpha 1(I) collagen promoter fusion genes in cultured calvariae from transgenic mice. The parent construct, ColCAT 3.6, contains 3520 basepairs of 5' rat alpha 1(I) collagen DNA, 115 basepairs of untranslated alpha 1(I) collagen-coding DNA, and the bacterial chloramphenicol acetyltransferase reporter gene, while the 5'-deletion ColCAT 2.3 contains 2296 kilobases of rat alpha 1(I) collagen promoter sequence. Transgenic mouse lines harboring these collagen promoter fusion genes were developed using the oocyte microinjection technique, and for each construct, three different lines of mice were tested. Calvariae from 6- to 8-day-old transgenic mice were cultured for 48 h with or without bovine PTH-(1-34). ColCAT 3.6 and ColCAT 2.3 were expressed at comparable levels in calvariae and were inhibited by PTH. There were parallel decreases in the incorporation of [3H]proline into collagen and levels of the endogenous alpha 1(I) collagen mRNA and transgene mRNA. Forskolin at 10 microM mimicked the inhibitory effect of PTH on promoter activity in ColCAT 3.6 and ColCAT 2.3 calvariae. A RNase protection assay showed that the transgene was initiated correctly from the transgene promoter. These data show that PTH and cAMP can repress collagen promoter activity in calvariae from transgenic mice, suggesting that the alpha 1(I) collagen promoter may contain cis elements down-stream of -2.3 kilobases that mediate PTH and cAMP repression of collagen gene expression in bone. Cultured bone explants from transgenic mice can be used as a model to study hormonal regulation of alpha 1(I) collagen promoter constructs.     

Vasoactive intestinal peptide induces both tyrosine hydroxylase activity and tetrahydrobiopterin biosynthesis in PC12 cells

Spike transmission probability between pyramidal cells and interneurons in the CA1 pyramidal layer was investigated in the behaving rat by the simultaneous recording of neuronal ensembles. Population synchrony was strongest during sharp wave (SPW) bursts. However, the increase was three times larger for pyramidal cells than for interneurons. The contribution of single pyramidal cells to the discharge of interneurons was often large (up to 0.6 probability), as assessed by the presence of significant (<3 ms) peaks in the cross-correlogram. Complex-spike bursts were more effective than single spikes. Single cell contribution was higher between SPW bursts than during SPWs or theta activity. Hence, single pyramidal cells can reliably discharge interneurons, and the probability of spike transmission is behavior dependent.     

Active signaling by Neu in transgenic mice

Transgenic mice engineered to overexpress the HER-2/neu/erbB-2 protooncogene under the control of a mammary-specific promoter develop mammary tumors and are a model for human breast cancer. Signal transduction by Neu was examined in situ in the tumors of these transgenic mice. This was accomplished using the PN2A monoclonal antibody, which recognizes Neu only in the phosphorylated, and therefore actively signaling, state. Immunohistochemistry using PN2A demonstrated that Neu actively signals in the tumors of Neu transgenic mice. Expression of Neu was always accompanied by co-overexpression of the endogenous epidermal growth factor receptor. Qualitatively similar results were found in mammary tumors from mice bitransgenic for the neu and transforming growth factor-alpha genes (both driven by the mouse mammary tumor virus promoter). Early mammary lesions demonstrated distinctive patterns of Neu activation relative to expression levels. Overexpression and activation were separable both temporally and spatially. These results refine the multi-step model for the role of Neu in mammary neoplasia and establish phosphorylation-state specific antibodies as a powerful tool for investigating tumor progression.