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Featured researches published by Tami C. Steveson.


Brain Behavior and Evolution | 1990

The molecular evolution of neuropeptides : prospects for the '90s

Robert M. Dores; Lorraine K. McDonald; Tami C. Steveson; Catherine A. Sei

Three distinct opioid precursors have been identified in the central nervous system of mammals: proopiomelanocortin (POMC), proenkephalin, and prodynorphin. These precursors are derived from separate genes, synthesized in distinct neurons, and yield unique sets of opioid end products. This review will discuss the general mechanisms involved in the biosynthesis of neuropeptide precursors and consider the roles of posttranscriptional and posttranslational processing mechanisms in the generation of multiple sets of end products from a single gene. In addition, techniques that can be used for isolating and characterizing neuropeptide genes, mRNAs, and end products will be reviewed. These introductory comments will serve as the framework for a discussion of the phylogeny of the opioid precursors in the major groups of non-mammalian vertebrates.


Neuroendocrinology | 1991

Differential Mechanisms for the N-Acetylation of Alpha-Melanocyte-Stimulating Hormone and Beta-Endorphin in the Intermediate Pituitary of the Frog, Xenopus laevis

Robert M. Dores; Tami C. Steveson; Kristin H. Lopez

Immunohistochemical analysis of the pituitary of Xenopus laevis revealed the colocalization of alpha-melanocyte-stimulating-hormone (MSH)-related immunoreactivity and N-acetyl-beta-endorphin-related immunoreactivity in the cells of the intermediate pituitary. In order to determine whether the immunoreactive N-acetylated beta-endorphin is released in parallel with the immunoreactive alpha-MSH, intermediate pituitaries were incubated in L-15 medium for 24 h. The medium and an acid extract of the intermediate pituitaries from each incubation were separately fractioned by a combination of gel filtration chromatography, reverse-phase high-performance liquid chromatography, and cation exchange chromatography. In the intermediate pituitary extract, the major form of alpha-MSH had chromatographic properties which corresponded to nonacetylated alpha-MSH (ACTH)(1-13)amide; whereas the major form of beta-endorphin had an apparent molecular weight of 1.2 kDa and was N-acetylated. The 1.2-kDa form of beta-endorphin and ACTH(1-13)amide were present in equimolar amounts. Analysis of the medium indicated that both end products were released in parallel. However, as reported in the literature, there was a significant increase in the N-acetylation of ACTH(1-13)amide during secretion. There was no further processing of beta-endorphin during secretion. Collectively, these observations indicate that in the intermediate pituitary of X. laevis there are separate mechanisms for the N-acetylation of alpha-MSH and beta-endorphin.


Annals of the New York Academy of Sciences | 1993

A View of the N‐Acetylation of α‐Melanocyte‐Stimulating Hormone and β‐Endorphin from a Phylogenetic Perspectivea

Robert M. Dores; Tami C. Steveson; Michelle L. Price

Low molecular weight polypeptide hormones and neuropeptides are synthesized on larger precursor proteins that are biologically inert.’ These precursors must undergo a series of posttranslational proteolytic cleavage events in order to liberate the biologically interesting sequences that may be interspersed within the sequence of the precursor.2 The end products generated as a result of these proteolytic cleavage events may undergo a number of additional posttranslational modifications including a-amidation, sulfation, and phosphorylation.2 For example, several neuropeptides are C-terminally amidated.3 N-terminal acetylation, however, is a less common posttranslational processing event. Among secreted polypeptides, only a-melanocyte-stimulating hormone (a-MSH) and p-endo~hin, end products of the proopiomelanocortin (POMC) biosynthetic pathway, undergo this posttranslational m~dification.~ This review will focus on the phylogeny of the POMC-specific N-acetyltransferase mechanisms that occur in the vertebrate intermediate pituitary. A case will be made that there is an “ancestral” POMC N-acetylating mechanism that has generally persisted throughout vertebrate evolution. In addition, a novel modification of this “general” scheme that is observed in anuran amphibians will be discussed at length.


Peptides | 1988

The isolation of multiple forms of β-endorphin from the intermediate pituitary of the Australian lungfish, Neoceratodus forsteri

Robert M. Dores; Tami C. Steveson; Jean M.P. Joss

The pituitary of the Australian lungfish, Neoceratodus forsteri, was screened immunohistochemically with heterologous antisera specific for either the C-terminal of mammalian beta-endorphin or the acetylated N-terminal of beta-endorphin. Immunopositive cells were only detected with the N-terminal specific antiserum; these cells were restricted to the intermediate pituitary. Acid extracts of the intermediate pituitary were fractionated by Sephadex gel filtration chromatography, CM cation exchange chromatography and reverse phase HPLC. Fractions were analyzed by radioimmunoassay (RIA) with a N-acetyl specific beta-endorphin RIA and by radioreceptor assay for the presence of opiate active forms of beta-endorphin. Both immunoreactive and opiate active forms of beta-endorphin were detected. Of the total beta-endorphin-related material isolated from the intermediate pituitary, approximately 97% was detected with the N-terminal specific RIA and approximately 3% was detected by the radioreceptor assay. The N-acetylated immunoreactive beta-endorphin could be separated into two forms. The major form had an apparent molecular weight of 3.2 Kda. This material had a net charge at pH 2.5 of +5. The minor form of immunoreactive beta-endorphin had an apparent molecular weight of 1.4 Kda and a net charge at pH 2.5 of +1. Neither immunoreactive form exhibited receptor binding activity in the radioreceptor assay. A single peak of opiate active beta-endorphin was detected. This material had an apparent molecular weight of 3.5 Kda and a net charge at pH 2.5 of +7.


Peptides | 1994

The posttranslational modification of β-endorphin in the intermediate pituitary of the toad, Bufo marinus, includes processing at a monobasic cleavage site

Robert M. Dores; Karen Gieseker; Tami C. Steveson

Fractionation of an acid extract of 15 B. marinus intermediate pituitaries by a combination of gel filtration chromatography and cation exchange chromatography revealed one major and five minor forms of beta-endorphin in this tissue. Based on reversed-phase HPLC and immunological properties, as well as amino acid composition and primary sequence analysis, it was deduced that the sequence of the major form of B. marinus beta-endorphin is N-acetyl-YGGFMTPE. Overall, the steady-state analyses of the minor forms of beta-endorphin indicated that the posttranslational processing of beta-endorphin in the toad intermediate pituitary includes endoproteolytic cleavage at both paired basic and monobasic cleavage sites.


Peptides | 1990

Detection of N-acetylated forms of β-endorphin and nonacetylated α-MSH in the intermediate pituitary of the toad, Bufo marinus

Tami C. Steveson; Cheryl L. Jennett; Robert M. Dores

Steady-state analysis of the acid extracts of the intermediate pituitary of the toad, Bufo marinus, revealed the presence of multiple forms of beta-endorphin and alpha-MSH. Approximately 98% of the immunoreactive beta-endorphin was N-acetylated. The major form of N-acetylated beta-endorphin, which represented 81.5% of the total beta-endorphin recovered from this tissue, had an apparent molecular weight of 1.2 kDa and a net charge of +1 at pH 2.75. Approximately 98% of the immunoreactive alpha-MSH present in the Bufo intermediate pituitary had reverse phase HPLC properties similar to the nonacetylated form of alpha-MSH, ACTH(1-13)amide. These observations are in agreement with studies on the intermediate pituitary of the frog, Xenopus laevis, which have shown that the N-acetylation of alpha-MSH in this species is a cosecretory processing event, whereas the N-acetylation of beta-endorphin is a posttranslational processing event (2, 5, 15). These observations indicate that the N-acetylation of beta-endorphin and alpha-MSH occurs at distinct subcellular sites in intermediate pituitary cells of anuran amphibians. The Bufo intermediate pituitary will serve as a good model system for studying these novel N-acetyltransferase reactions.


General and Comparative Endocrinology | 1992

Detection and partial characterization of proopiomelanocortin-related end-products from the pars intermedia of the toad, Bombina orientalis

Robert M. Dores; Trang Truong; Tami C. Steveson

Steady-state analyses were performed on the proopiomelanocortin (POMC)-related end-products present in acid extracts of the pars intermedia of the anuran amphibian, Bombina orientalis. Sephadex G-75 gel filtration chromatography indicated that immunoreactive alpha-MSH-sized material and N-acetylated beta-endorphin-related material are the major POMC-related products present in this tissue. The alpha-MSH-sized immunoreactivity was further fractionated by reversed phase HPLC. The major peak of immunoreactivity isolated by this procedure eluted with the same retention time as synthetic ACTH(1-13)amide. Cation exchange chromatography supported the conclusion that the major storage form of alpha-MSH in the pars intermedia of Bombina is ACTH(1-13)amide. Analysis of Bombina pars intermedia in culture indicated that mono-acetylated and di-acetylated alpha-MSH were the major forms of alpha-MSH secreted into the medium. The major peak of N-acetylated beta-endorphin-related material was further analyzed by cation exchange chromatography and Sephadex G-25 gel filtration column chromatography. The major storage form of beta-endorphin in this tissue is N-acetylated, has a net positive charge at pH 2.75 of +1, and has an apparent molecular weight of 1.2K. The beta-endorphin present in the pars intermedia of this tissue does not undergo further N-acetylation at the time of secretion. These results indicate that in the pars intermedia of the archaeobatrachian, Bombina orientalis, the N-acetylation of alpha-MSH is a cosecretory processing event, whereas N-acetylation of beta-endorphin is a post-translational processing event. These results are compared to other archaeobatrachian and neobatrachian pituitary POMC systems that have been analyzed.


Neuroendocrinology | 1994

Melanotropes of the Lizard, Anolis carolinensis, Lack N-Acetylating Mechanisms for Both Alpha-Melanocyte-Stimulating Hormone and Beta-Endorphin

Robert M. Dores; Heidi Wasinger; David Vaudry; Tami C. Steveson; Ana Lancha

In order to determine whether Anolis carolinensis intermediate pituitary cells have the capacity to N-acetylate either ACTH(1-13)NH2 or beta-endorphin during secretion, individual intermediate pituitary explants were incubated in DMEM/CO2 for 24 h at 28 degrees C. Although alpha-melanocyte-stimulating hormone (alpha-MSH)- and beta-endorphin-related products were spontaneously released into the medium, none of these forms were N-acetylated. It appears that unlike most gnathostomes, A. carolinensis has secondarily lost the POMC-specific N-acetylation mechanisms. A ramification of this observation is that the alpha-MSH for A. carolinensis is ACTH(1-13)NH2.


Brain Behavior and Evolution | 1990

The Molecular Evolution of Neuropeptides: Prospects for the '90s (Part 2 of 2)

Robert M. Dores; Lorraine K. McDonald; Tami C. Steveson; Catherine A. Sei

Three distinct opioid precursors have been identified in the central nervous system of mammals: proopiomelanocortin (POMC), proenkephalin, and prodynorphin. These precursors are derived from separate genes, synthesized in distinct neurons, and yield unique sets of opioid end products. This review will discuss the general mechanisms involved in the biosynthesis of neuropeptide precursors and consider the roles of posttranscriptional and posttranslational processing mechanisms in the generation of multiple sets of end products from a single gene. In addition, techniques that can be used for isolating and characterizing neuropeptide genes, mRNAs, and end products will be reviewed. These introductory comments will serve as the framework for a discussion of the phylogeny of the opioid precursors in the major groups of non-mammalian vertebrates.


General and Comparative Endocrinology | 1992

Detection and partial characterization of proopiomelanocortin-related end-products from the pars intermedia of the toad,

Robert M. Dores; Thai V. Truong; Tami C. Steveson

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Ana Lancha

University of La Laguna

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Marcela Dueñas

Spanish National Research Council

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