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S A Camper

Publications and source records attributed to S A Camper.

18 recordsLinked to original sources
PubMed1992

raf regulates the postnatal repression of the mouse alpha-fetoprotein gene at the posttranscriptional level.

The mouse alpha-fetoprotein (AFP) gene is transcribed at a high rate in liver during the second half of gestation. Its steady-state mRNA levels decrease 10(4)-fold shortly after birth, at least in part as the consequence of a dramatic decrease in its transcription rate. The final basal level of AFP mRNA in adult liver is influenced by a trans-acting locus on chromosome 15 termed raf. Two strategies were used to demonstrate that the raf gene acts posttranscriptionally to affect the processing and/or stability of AFP transcripts. Transgenic mouse studies demonstrated that raf gene action is independent of both positive and negative transcription control elements of the AFP gene. Nuclear run-on analysis was used to confirm that transcriptions of both AFP transgenes and another endogenous raf-responsive gene, H19, are invariant with respect to the raf genotype. Thus, the postnatal repression of the AFP gene is mediated by both transcriptional and posttranscriptional mechanisms.

Albumins↗
PubMed1992

Morphologic effects of hGRH gene expression on the pituitary, liver, and pancreas of MT-hGRH transgenic mice. An in situ hybridization analysis.

Morphologic changes in the pituitary, liver, and pancreas of mice with the metallothionein-human growth hormone--releasing hormone (MT-hGRH) transgene were analyzed by in situ hybridization histochemistry (ISH). There was progression from somatotroph hyperplasia to neoplasia in pituitaries of transgenic mice. Pituitary neoplasms were present between 9 to 12 months of age in some mice. Magnetic resonance imaging (MRI) readily identified enlarged pituitaries in MT-hGRH transgenic mice. Serum mouse GH and hGRH levels were marked elevated in MT-hGRH transgenic mice. In situ hybridization histochemistry showed mRNA for hGRH in liver, pituitary, pancreas, spleen, and in most other tissues examined. Combined ISH and immunohistochemistry in the pituitary gland showed that some of the GH cells also produced hGRH, and ultrastructural immunohistochemical analysis of pituitaries showed that GH and hGRH were localized in the same cell and within the same secretory granules. Liver cells of MT-hGRH transgenic mice showed evidence of hypertrophy, and the pancreatic islets were hyperplastic with significant increases in the islet cell areas. The morphologic changes in the liver were distinctive enough to separate control littermates from MT-hGRH transgenic mice in all cases. The enlarged pancreatic islets had increased numbers of insulin-producing cells. Immunoreactive hGRH and hGRH mRNA were both localized in islet cells, and an intense hybridization signal of hGRH mRNA, but only weak staining for hGRH protein, were detected in the liver of transgenic mice. These results indicate that excessive hGRH production leads to distinct morphologic changes in various organs in MT-hGRH transgenic mice and that there is temporal progression from hyperplasia to adenomatous somatotrophs in pituitaries with chronic stimulation by hGRH that involves paracrine, endocrine, and autocrine mechanisms.

Adenoma↗
PubMed1992

Functional analyses of albumin expression in a series of hepatocyte cell lines and in primary hepatocytes.

A series of simian virus 40-immortalized hepatocyte cell lines which are heterogeneous with regard to expression of albumin protein and RNA were characterized for their ability to transcribe the albumin gene. Nascent chain extension assay showed that albumin RNA levels in these cells were determined predominantly at the transcription level. The albumin promoter and enhancer sequences were fused to the bacterial chloramphenicol acetyltransferase gene; the ability of the resulting expression constructs to drive chloramphenicol acetyltransferase expression after transfection into these hepatocyte cell lines was measured. The activity of the albumin promoter and enhancer constructs in primary hepatocytes was also measured. The albumin promoter was expressed differentially in these cells; however, no correlation was found between the transcriptional efficiency of the transfected albumin promoter and endogenous albumin transcription. The albumin enhancer was functional in some but not all albumin-positive cells. The minimal albumin enhancer was mapped to a 330-base pair fragment extending from -9.94 kilobases (kb) to -10.27 kb; three elements within this fragment recently shown to be necessary for enhancer function in a murine hepatocyte cell line were also essential for albumin enhancer function in the rat hepatocyte cell line CWSV1. A transcriptional silencer was identified which could suppress the expression of the homologous albumin promoter and the heterologous herpes simplex virus thymidine kinase promoter. Preliminary analysis localized the albumin silencer between -11 and -12 kb. Our results suggest that multiple regulatory sequences may act cooperatively to determine efficient tissue-specific expression of the albumin gene.

Albumins↗
PubMed1991

Influence of a V kappa 8 L chain transgene on endogenous rearrangements and the immune response to the HA(Sb) determinant on influenza virus.

A rearranged murine V kappa 8/J kappa 5 L chain gene that codes for the L chain of most antibodies generated in the primary response of BALB/c mice to the antigenic site, Sb, of the hemagglutinin (HA) molecule of influenza virus A/PR/8/34 (PR8) has been cloned. Three transgenic lines were generated by microinjecting the gene. Lines Ga and L each contain a single copy of the transgene whereas line Gb contains three complete copies. Mice of the Ga lineage showed increased V kappa 8-specific mRNA levels only in spleen, but not in nonlymphoid organs and therefore displayed apparently normal lymphoid-specific regulation of the Ig transgene. B cell hybridomas generated from these mice were analyzed for rearrangements of endogenous V kappa genes. Greater than 90% of the C kappa alleles were retained in germ-line configuration in the Ga line, compared with only 0 to 18% in the L line. Thus, a wide variation in the frequency of endogenous rearrangements is seen among mice of different lineages using the same transgene construct. None of more than 150 hybridomas derived from LPS-stimulated splenic B cells of Ga mice exhibited HA-binding activity although they expressed the transgene and, in most cases, excluded endogenous V kappa rearrangements. In contrast, a large fraction of hybridomas isolated after primary immunization with PR8 were HA(Sb)-specific. This indicated that the transgene was functional but formed HA-specific antibodies with a more restricted set of H chains than previously hypothesized. The primary anti-HA response to immunization with PR8 was diminished in all lines compared with normal mice except for a slightly accelerated but transient burst of anti-HA antibody formation in two out of three lines (Ga and Gb). This early response in G lineage mice was largely specific for HA(Sb) and thus appeared to be composed of transgene-expressing antibodies. No differences in serum titers were observed in the secondary anti-HA responses to booster inoculation with PR8 between transgenic and normal mice.

Animals↗
PubMed1991

Expression of anti-DNA immunoglobulin transgenes in non-autoimmune mice.

Self-reactive B cells can be regulated by either deletion or inactivation. These manifestations of self-tolerance have been dramatically shown in transgenic mice in which the number of self-reactive cells has been artificially expanded. We have now extended these models to ask if B-cell tolerance as described for non-disease-associated antigens also operates for the targets of autoimmunity. The target we have chosen is DNA. Anti-DNA antibodies are diagnostic of certain autoimmune syndromes in humans and are a characteristic of the murine model of systemic autoimmunity, the MRl/lpr mouse. Antibodies to both single-stranded and double-stranded DNA have been implicated in disease. By generating anti-DNA transgenic mice, we have addressed the question of whether DNA-specific B cells are regulated in normal (non-autoimmune) mice. We indeed found that most transgenic B cells bind DNA, yet we failed to detect secreted anti-DNA. We suggest that as a consequence of their self-reactivity these B cells are developmentally arrested.

Animals↗
PubMed1991

Localization of the panhypopituitary dwarf mutation (df) on mouse chromosome 11 in an intersubspecific backcross.

Ames dwarf (df) is an autosomal recessive mutation characterized by severe dwarfism and infertility. This mutation provides a mouse model for panhypopituitarism. The dwarf phenotype results from failure in the differentiation of the cells which produce growth hormone, prolactin, and thyroid stimulating hormone. Using the backcross (DF/B-df/df X CASA/Rk) X DF/B-df/df, we confirmed the assignment of df to mouse chromosome 11 and demonstrated recombination between df and the growth hormone gene. This backcross is an invaluable resource for screening candidate genes for the df mutation. The df locus maps to less than 1 cM distal to Pad-1 (0.85 +/- 0.85 cM). Two new genes localized on mouse chromosome 11, Rpo2-1, and Edp-1, map to a region of conserved synteny with human chromosome 17. The localization of the alpha 1 adrenergic receptor, Adra-1, extends a known region of synteny conservation between mouse chromosome 11 and human chromosome 5, and suggests that a human counterpart to df would map to human chromosome 5.

Animals↗
PubMed1991

Targeted ablation of pituitary gonadotropes in transgenic mice.

LH, FSH, and TSH are heterodimeric glycoprotein hormones composed of a common alpha-subunit and unique beta-subunits. The alpha-subunit is produced in two distinct specialized cell types of the pituitary gland: gonadotropes, which synthesize LH and FSH, and thyrotropes, which synthesize TSH. We have demonstrated that 313 base pairs of the bovine-alpha subunit promoter direct expression of diphtheria toxin A chain specifically to the gonadotropes in transgenic mice. Animals carrying this transgene generally exhibit reproductive failure and lack of gonadal differentiation, consistent with gonadotrope ablation. Lack of gonadotrope activity was verified by RIA and immunohistochemical staining for LH. The phenotype of these transgenic mice is nearly identical to mice homozygous for the spontaneous mutation, hpg, which is due to a deletion in the gene encoding GnRH. Thyrotrope function was judged normal based on overall growth of the animals, appearance of their thyroids, T4 levels measured by RIA, and immunohistochemical staining for TSH. The ablation of gonadotropes but not thyrotropes suggests that separate cis-acting elements are necessary for expression of the alpha-subunit gene in these two cell types. Pituitary content of ACTH and GH was apparently normal, while PRL synthesis and storage were reduced. Thus, in a pituitary almost completely devoid of gonadotropes, most other pituitary functions were normal. This suggests that most pituitary cells are able to differentiate independently of terminal gonadotrope differentiation and can function in the absence of paracrine signaling provided by gonadotropes.

Adrenocorticotropic Hormone↗
PubMed1990

The Pit-1 transcription factor gene is a candidate for the murine Snell dwarf mutation.

Two nonallelic mouse mutations with severe dwarf phenotypes are characterized by a lack of growth hormone, prolactin, and thyroid stimulating hormone. The cells that normally synthesize these pituitary hormones express a common transcription factor called GHF-1 or Pit-1. Using an intersubspecific backcross, we have demonstrated tight linkage of the Pit-1 and Snell dwarf (dw) genes on mouse chromosome 16. No recombination was observed between Pit-1 and dw in 110 individuals examined. Southern blot analysis of genomic DNA reveals that the Pit-1 gene is rearranged in C3H/HeJ-dwJ/dw mice but not in coisogenic +/+ animals, providing molecular evidence that a lesion in the Pit-1 gene results in the Snell dwarf phenotype. Demonstration of low levels of Pit-1 expression in Ames dwarf (df) mice implies that both Pit-1 and df expression may be required for pituitary differentiation.

Animals↗
PubMed1989

Postnatal repression of the alpha-fetoprotein gene is enhancer independent.

The mammalian liver undergoes a number of dramatic changes in gene expression during development. One of these is typified by the alpha-fetoprotein (AFP) gene, which is activated in the fetal liver but undergoes a transcriptional decline at birth. In contrast, although activated at the same time during fetal development, albumin gene transcription is maintained at high levels in adult animals. To determine whether the postnatal decline in AFP gene transcription is mediated through its distal enhancers or through more proximal elements surrounding the promoter or structural gene, chimeric genes bearing substitutions of albumin gene cis-acting elements for the equivalent AFP gene elements were introduced into the germ line of mice. The expression of the transgenes was then analyzed at various stages of development. Our results indicate that the AFP gene enhancers are not involved in the postnatal decline in AFP transcription. Rather, a region within the first kilobase of DNA upstream of the AFP gene, including its promoter, and/or portions of the structural gene is sufficient to direct postnatal repression of the gene.

Aging↗
PubMed1987

Diversity of alpha-fetoprotein gene expression in mice is generated by a combination of separate enhancer elements.

The 5' flanking region of the mouse alpha-fetoprotein (AFP) gene contains a tissue-specific promoter and three upstream regulatory elements that behave as classical enhancers. At least one of these enhancers is now shown to be required for the tissue-specific expression of the AFP gene when it is introduced into the mouse genome by microinjection of cloned DNA fragments into fertilized eggs. Each enhancer can direct expression in the appropriate tissues, the visceral endoderm of the yolk sac, the fetal liver, and the gastrointestinal tract, but each exerts different influence in these three tissues. These differences may explain the tissue-specific diversity in the levels of expression characteristic of the AFP gene. The postnatal repression of transcription of the AFP gene in both liver and gut, as well as the reinitiation of its transcription during liver regeneration, is mimicked by the introduced gene when it is linked to the enhancer domains together or singly. Thus, the DNA sequence elements responsible for directing the activation of AFP transcription, its repression, and reinduction are contained in a limited segment of DNA within or 5' to the gene (or both) and are operative in the absence of the closely linked albumin gene.

Animals↗
PubMed1985

Hormonal regulation of the bovine prolactin promoter in rat pituitary tumor cells.

A 1-kilobase DNA fragment containing the promoter of the bovine prolactin gene was fused to the chloramphenicol acetyltransferase gene and the activity of the promoter was assayed by transfection of the fusion gene into COS-1, HeLa, and GH3 cells. Transcription of the chloramphenicol acetyltransferase gene driven by the prolactin promoter was detected only in GH3 cells, a rat pituitary tumor cell line. Epidermal growth factor and thyroid releasing hormone produced a stimulation of transcription, and the synthetic glucocorticoid hormone dexamethasone effected an inhibition of transcription from the prolactin promoter. None of these factors significantly affected transcription of the chloramphenicol acetyltransferase gene fused to the Rous sarcoma virus promoter. Deletion of all but 250 base pairs of bovine prolactin 5'-flanking DNA had no effect, indicating that the signals sufficient for both stimulation and inhibition of transcription reside in close proximity to the promoter.

Acetyltransferases↗