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S G Amara

Publications and source records attributed to S G Amara.

85 records · Page 5Linked to original sources
PubMed1984

Calcitonin/calcitonin gene-related peptide transcription unit: tissue-specific expression involves selective use of alternative polyadenylation sites.

Different 3' coding exons in the rat calcitonin gene are used to generate distinct mRNAs encoding either the hormone calcitonin in thyroidal C-cells or a new neuropeptide referred to as calcitonin gene-related peptide in neuronal tissue, indicating the RNA processing regulation is one strategy used in tissue-specific regulation of gene expression in the brain. Although the two mRNAs use the same transcriptional initiation site and have identical 5' terminal sequences, their 3' termini are distinct. The polyadenylation sites for calcitonin and calcitonin gene-related peptide mRNAs are located at the end of the exons 4 and 6, respectively. Termination of transcription after the calcitonin exon does not dictate the production of calcitonin mRNA, because transcription proceeds through both calcitonin and calcitonin gene-related peptide exons irrespective of which mRNA is ultimately produced. In isolated nuclei, both polyadenylation sites appear to be utilized; however, the proximal (calcitonin) site is preferentially used in nuclei from tissues producing calcitonin mRNA. These data suggest that the mechanism dictating production of each mRNA involves the selective use of alternative polyadenylation sites.

Animals↗
PubMed1984

Alternative RNA processing events as a critical developmental regulatory strategy in neuroendocrine gene expression.

Alternative RNA processing events, consequential to alternative poly(A) site selection, represent the critical developmental strategy dictating the tissue-specific pattern of the polypeptide product production in calcitonin gene expression. The consequence of these events is the production of an mRNA encoding the precursor of a novel neuropeptide, referred to as CGRP, in the brain and an mRNA encoding the precursor to calcitonin in the thyroidal C cells. A trans-acting mechanism appears to adjudicate the critical choice of poly(A) site. It is suggested that this type of RNA processing regulation is a commonly used mechanism, of particular importance in expression of genes modulating neural developmental events.

Amino Acid Sequence↗
PubMed1982

Alternative RNA processing in calcitonin gene expression generates mRNAs encoding different polypeptide products.

Alternative processing of RNA transcripts from the calcitonin gene results in the production of distinct mRNAs encoding the hormone calcitonin or a predicted product referred to as calcitonin gene-related peptide (CGRP). The calcitonin mRNA predominates in the thyroid while the CGRP-specific mRNA appears to predominate in the hypothalamus. These observations lead us to propose a model in which developmental regulation of RNA processing is used to increase the diversity of neuroendocrine gene expression.

Animals↗
PubMed1982

Calcitonin COOH-terminal cleavage peptide as a model for identification of novel neuropeptides predicted by recombinant DNA analysis.

A strategy is presented for identification of putative neurohormones that were predicted by sequence analysis of recombinant cDNa molecules. The nucleotide sequence of a cloned calcitonin cDNA insert predicts that the proteolytic excision of calcitonin from a 136-amino acid precursor should generate two additional peptides derived from regions flanking the calcitonin sequence on the NH2 and carboxyl termini. The predicted 16-amino acid COOH-terminal cleavage peptide (NH2-Asp-Met-Ala-Lys-Asp-Leu-Glu-Thr-Asn-His-His-Pro-Thr-Phe-Gly-Asn-COOH) was chemically synthesized using solid phase procedures. Antibodies against this synthetic hexadecapeptide detect immunologically cross-reactive material in tissue extracts from normal thyroid glands and calcitonin-producing medullary thyroid carcinomas. Each of the four calcitonin mRNA-directed cell-free translation products contain the immunological determinants for both calcitonin and the COOH-terminal cleavage peptide.

Amino Acid Sequence↗
PubMed1982

Calcitonin mRNA polymorphism: peptide switching associated with alternative RNA splicing events.

Evidence is presented which supports a model proposing that differential RNA splicing events may be used in expression of genes of the endocrine system to generate alternative polypeptide hormones. We previously reported that variation in the expression of the gene encoding the small polypeptide hormone calcitonin is associated with the production of a new calcitonin-like or pseudo-calcitonin (psi Cal) mRNA. A plasmid containing psi Cal cDNA sequences has been constructed, and calcitonin genomic clones have been isolated. Hybridization analysis reveals that calcitonin and psi Cal sequences are chromosomally linked and are present in the same nuclear RNA transcripts. Both calcitonin and psi Cal mRNAs are functional and encode different polypeptide products. These data are compatible with the proposed model that alternative RNA splicing of the transcript(s) of the calcitonin gene ultimately results in the production of different polypeptide products.

Amino Acid Sequence↗
PubMed1982

RNA processing regulation of neuroendorcrine gene expression.

Alternative RNA processing events account for biological polymorphism in the endocrine, immune, and other systems; these may have possible widespread significance in the regulation of eukaryotic gene expression. The selective use of alternative hormone-encoding exons can produce multiple mRNAs generating different protein products. The resultant "peptide switching" is a previously unrecognized mechanism allowing a single gene to encode different hormones in different tissues and thus increases the diversity of endocrine gene expression.

Animals↗
PubMed1981

Altered expression of the calcitonin gene associated with RNA polymorphism.

The selective control of gene expression results in diversified morphology and physiological function. Understanding the expression of differentiated function in molecular terms requires detailed characterization of the regulation of mRNA synthesis and catabolism. Although considerable emphasis has been placed on transcriptional control, the discovery of HnRNA and 'split genes' gives rise to the possibility of post-transcriptional regulation at the level of processing of nuclear precursors. A rat calcitonin-producing medullary thyroid carcinoma (MTC) line was used as a model for definition of certain aspects in regulation of gene expression. Serial transplantation of several rat MTC lines containing and secreting large amounts of calcitonin generated tumours in which calcitonin biosynthesis was decreased more than 10-fold. We report here that the conversion from a 'high' to a 'low' calcitonin producing state is associated with specific modifications of the calcitonin mRNA synthetic pathway and a consequence of these changes seems to be the production of a new cytoplasmic mRNA.

Animals↗
PubMed1980

Identification of the putative cell-free translation product of rat calcitonin mRNA.

Messenger RNA from calcitonin-secreting rat medullary thyroid carcinoma lines directs the synthesis of a putative precursor of calcitonin when translated in wheat embryo lysate. The major translation product directed by mRNA isolated from a rat tumor with a calcitonin content representing greater than 2% of the total protein mass has an apparent molecular weight of 17,500 when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Immunoprecipitations of the cell-free translation products demonstrate that the 17,500-dalton protein has immunologic determinants which are specifically recognized by antisera to calcitonin. In addition, the relative prominence of this protein is significantly diminished when mRNA from lines with low calcitonin content is used to direct cell-free protein synthesis. This evidence suggests that the initial translation product of calcitonin mRNA is a 17,500-dalton species which must undergo subsequent processing to generate the secreted polypeptide.

Animals↗
PubMed1980

Characterization of rat calcitonin mRNA.

A chimeric plasmic containing cDNA complementary to rat calcitonin mRNA has been constructed. Partial sequence analysis shows that the insert contains a nucleotide sequence encoding the complete amino acid sequence of calcitonin. Two basic amino acids precede and three basic amino acids follow the hormone sequence, suggesting that calcitonin is generated by the proteolytic cleavage of a larger precursor in a manner analogous to that of other small polypeptide hormones. The COOH-terminal proline, known to be amidated in the secreted hormone, is followed by a glycine in the precursor. The cloned calcitonin DNA was used to characterize the expression of calcitonin mRNA. Cytoplasmic mRNAs from calcitonin-producing rat medullary thyroid carcinoma lines and from normal rat thyroid glands contain a single species, 1050 nucleotides long, whch hybridizes to the cloned calcitonin cDNA. The concentration of calcitonin mRNA sequences is greater in those tumors that produce larger amounts of immunoreactive calcitonin. RNAs from other endocrine tissues, including anterior and neurointermediate lobes of rat pituitary, contain no detectable calcitonin mRNA.

Amino Acid Sequence↗
PubMedDate not supplied

Neurotransmitter transporters as molecular targets for addictive drugs.

The neurotransmitter dopamine lies at or near the center of current theories of drug abuse and dependence. Multiple lines of evidence indicate that dopaminergic cells play key roles in a variety of motivated behaviors. Accordingly, it is not surprising that cocaine and amphetamines--some of the most widely used illicit drugs--elevate extraneuronal dopamine concentrations through their actions on the plasma membrane dopamine transporter. From the point of view of developing novel pharmacological interventions for the treatment or prevention of psychostimulant abuse, practical benefits may arise from an improved understanding of how neurotransmitter transporters operate and how drugs interact with them.

Amphetamines↗
PubMedDate not supplied

Production of a novel neuropeptide encoded by the calcitonin gene via tissue-specific RNA processing.

Alternative processing of the RNA transcribed from the calcitonin gene appears to result in the production of a messenger RNA in neural tissue distinct from that in thyroidal 'C' cells. The thyroid mRNA encodes a precursor to the hormone calcitonin whereas that in neural tissues generates a novel neuropeptide, referred to as calcitonin gene-related peptide (CGRP). The distribution of CGRP-producing cells and pathways in the brain and other tissues suggests functions for the peptide in nociception, ingestive behaviour and modulation of the autonomic and endocrine systems. The approach described here permits the application of recombinant DNA technology to analyses of complex neurobiological systems in the absence of prior structural or biological information.

Amino Acid Sequence↗
PubMedDate not supplied

Stimulation of noradrenergic sympathetic outflow by calcitonin gene-related peptide.

Alternative splicing of RNA transcripts from the calcitonin gene produces mRNAs that encode different polypeptides. While the mRNA encoding calcitonin predominates in thyroidal 'C' cells, calcitonin gene-related peptide (CGRP) mRNA appears to be the major mRNA component in non-thyroid tissue, including brain. The predicted peptide arising from translation of CGRP mRNA has now been identified immunocytochemically throughout the central and peripheral nervous systems. CGRP, a 37-residue peptide, is distributed in brain pathways subserving sensory, motor and autonomic functions. We report here that CGRP acts in the central nervous system to stimulate selectively noradrenergic sympathetic outflow.

Animals↗