Biomedical subjects

B A Morgan

Publications and source records attributed to B A Morgan.

At least 19 recordsLinked to original sources

PubMed2001

Redox control of AP-1-like factors in yeast and beyond.

Cells have evolved complex and efficient strategies for dealing with variable and often-harsh environments. A key aspect of these stress responses is the transcriptional activation of genes encoding defense and repair proteins. In yeast members of the AP-1 family of proteins are required for the transcriptional response to oxidative stress. This sub-family of AP-1 (called yAP-1) proteins are sensors of the redox-state of the cell and are activated directly by oxidative stress conditions. yAP-1 proteins are bZIP-containing factors that share homology to the mammalian AP-1 factor complex and bind to very similar DNA sequence sites. The generation of reactive oxygen species and the resulting potential for oxidative stress is common to all aerobically growing organisms. Furthermore, many of the features of this response appear to be evolutionarily conserved and consequently the study of model organisms, such as yeast, will have widespread utility. The important structural features of these factors, signaling pathways controlling their activity and the nature of the target genes they control will be discussed.

Animals↗

PubMed2001

Peroxide sensors for the fission yeast stress-activated mitogen-activated protein kinase pathway.

The Schizosaccharomyces pombe stress-activated Sty1p/Spc1p mitogen-activated protein (MAP) kinase regulates gene expression through the Atf1p and Pap1p transcription factors, homologs of human ATF2 and c-Jun, respectively. Mcs4p, a response regulator protein, acts upstream of Sty1p by binding the Wak1p/Wis4p MAP kinase kinase kinase. We show that phosphorylation of Mcs4p on a conserved aspartic acid residue is required for activation of Sty1p only in response to peroxide stress. Mcs4p acts in a conserved phospho-relay system initiated by two PAS/PAC domain-containing histidine kinases, Mak2p and Mak3p. In the absence of Mak2p or Mak3p, Sty1p fails to phosphorylate the Atf1p transcription factor or induce Atf1p-dependent gene expression. As a consequence, cells lacking Mak2p and Mak3p are sensitive to peroxide attack in the absence of Prr1p, a distinct response regulator protein that functions in association with Pap1p. The Mak1p histidine kinase, which also contains PAS/PAC repeats, does not regulate Sty1p or Atf1p but is partially required for Pap1p- and Prr1p-dependent transcription. We conclude that the transcriptional response to free radical attack is initiated by at least two distinct phospho-relay pathways in fission yeast.

Activating Transcription Factor 1↗

PubMed2001

The application of lead isotope analysis to bullet individualization in two homicides.

Bullets were characterized by lead isotope ratio analysis and trace element analysis in two homicides. In one case, we concluded that a fatal bullet did not share a common origin with bullets in a box of ammunition containing 24 cartridges taken from suspects. Evidence in the second case included two bullets from the crime scene and 163 bullets taken from various suspects. We were able to infer that the two bullets from the crime scene did not share a common origin and that they differed from all of the bullets taken from suspects. All of the suspects' ammunition had been reloaded as was evident both from trace and isotopic analysis and, indeed, from visual inspection.

Journal Article↗

PubMed2000

The forkhead protein Fkh2 is a component of the yeast cell cycle transcription factor SFF.

In the yeast Saccharomyces cerevisiae, the MADS-box protein Mcm1, which is highly related to mammalian SRF (serum response factor), forms a ternary complex with SFF (Swi five factor) to regulate the cell cycle expression of genes such as SWI5, CLB2 and ACE2. Here we show that the forkhead protein Fkh2 is a component of SFF and is essential for ternary complex formation on the SWI5 and ACE2 promoters. Fkh2 is essential for the correct cell cycle periodicity of SWI5 and CLB2 gene expression and is phosphorylated with a timing that is consistent with a role in this expression. Furthermore, investigation of the relationship between Fkh2 and a related forkhead protein Fkh1 demonstrates that these proteins act in overlapping pathways to regulate cell morphology and cell separation. This is the first example of a eukaryotic transcription factor complex containing both a MADS-box and a forkhead protein, and it has important implications for the regulation of mammalian gene expression.

Cell Cycle↗

PubMed2000

Wnt signaling maintains the hair-inducing activity of the dermal papilla.

The formation of the hair follicle and its cyclical growth, quiescence, and regeneration depend on reciprocal signaling between its epidermal and dermal components. The dermal organizing center, the dermal papilla (DP), regulates development of the epidermal follicle and is dependent on signals from the epidermis for its development and maintenance. GFP specifically expressed in DP cells of a transgenic mouse was used to purify this population and study the signals required to maintain it. We demonstrate that specific Wnts, but not Sonic hedgehog (Shh), maintain anagen-phase gene expression in vitro and hair inductive activity in a skin reconstitution assay.

Animals↗

PubMed2000

Chemical synthesis and receptor binding of catfish somatostatin: a disulfide-bridged beta-D-Galp-(1-->3)-alpha-D-GalpNAc O-glycopeptide.

The glycopeptide hormone catfish somatostatin (somatostatin-22) has the amino acid sequence H-Asp-Asn-Thr-Val-Thr-Ser-Lys-Pro-Leu-Asn-Cys-Met-Asn-Tyr-Phe-Trp-Lys-Se r-Arg-Thr-Ala-Cys-OH; it includes a cyclic disulfide connecting the two Cys residues, and the major naturally occurring glycoform contains D-GalNAc and D-Gal O-glycosidically linked to Thr5. The linear sequence was assembled smoothly starting with an Fmoc-Cys(Trt)-PAC-PEG-PS support, using stepwise Fmoc solid-phase chemistry. In addition to the nonglycosylated peptide, two glycosylated forms of somatostatin-22 were accessed by incorporating as building blocks, respectively, Nalpha-Fmoc-Thr(Ac3-alpha-D-GalNAc)-OH and Nalpha-Fmoc-Thr(Ac4-beta-D-Gal-(1-->3)-Ac2-alpha-D-GalNAc)-O H. Acidolytic deprotection/cleavage of these peptidyl-resins with trifluoroacetic acid/scavenger cocktails gave the corresponding acetyl-protected glycopeptides with free sulfhydryl functions. Deacetylation, by methanolysis in the presence of catalytic sodium methoxide, was followed by mild oxidation at pH 7, mediated by Nalpha-dithiasuccinoyl (Dts)-glycine, to provide the desired monomeric cyclic disulfides. The purified peptides were tested for binding affinities to a panel of cloned human somatostatin receptor subtypes; in several cases, presence of the disaccharide moiety resulted in 2-fold tighter binding.

Amino Acid Sequence↗

PubMed2000

Thioredoxin peroxidase is required for the transcriptional response to oxidative stress in budding yeast.

A genetic screen was performed in Saccharomyces cerevisiae to identify mechanisms important for the transcriptional activation of genes encoding antioxidant proteins. Thioredoxin peroxidase, Tsa1p, of the thioredoxin system, was found to be essential for the transcriptional induction of other components of the thioredoxin system, TRX2 (thioredoxin) and TRR1 (thioredoxin reductase), in response to H(2)O(2). The expression of TRX2 and TRR1 is known to be regulated by the transcription factors Yap1p and Skn7p in response to H(2)O(2), and the Tsa1p-dependent regulation of TRX2 requires the Yap1p/Skn7p pathway. The data suggest that expression of components of the thioredoxin system is dependent on the activity of Tsa1p in response to H(2)O(2) in a Yap1p/Skn7p-dependent pathway.

Animals↗

PubMed1999

Synthesis and binding properties of cyclohexapeptide somatostatin analogs containing naphthylalanine and arylalkyl peptoid residues.

We report the synthesis, binding affinities to the recombinant human somatostatin receptors, and structure-activity relationship studies of compounds related to the cyclic hexapeptide, c-[Pro6-Phe7-D-Trp8Lys9-Thr10-Phe11], L-363,301 (the numbering in the sequence refers to the position of the residues in native somatostatin). The Pro residue in this compound is replaced with the arylalkyl peptoid residues Nphe (N-benzylglycine), (S)betaMeNphe [(S)-N-[alpha(-methyl)benzyl]glycine] or (R)betaMeNphe [(R)-N-[(alpha-methyl)benzyl]glycine] and L-1-naphthylalanine is incorporated into either position 7 or 11 of the parent compound. The synthesis and binding data of the Nnal6 ([N-naphthylmethyl]glycine) analog of L-363,301 is also reported. The incorporation of the Nnal residue into position 6 of L-363,301 resulted in an analog with weaker binding affinities to all hsst receptors but enhanced selectivity towards the hsst2 receptor compared with the parent compound. The other compounds bind effectively to the hsst2 receptor but show some variations in the binding to the hsst3 and hsst5 receptors resulting in different ratios of binding affinities to the hsst5 and hsst2 or hsst3 and hsst2, respectively. The incorporation of the Nphe residue into position 6 and the Nal residue into position 7 of L-363,301 led to a compound which binds potently to the hsst2 and has increased selectivity towards this receptor (weaker binding to hsst3 and hsst5 receptors) compared with the parent compound. The analogs with beta-methyl chiral substitutions in the aromatic peptoid side chain and Nal in position 7 or 11 bind effectively to the hsst2 and hsst5 receptors. They exhibit similar ratios of binding affinities to the hsst5 and hsst2 receptors as observed for L-363,301. There are however minor differences in binding to the hsst3 receptor among these analogs. These studies allow us to investigate the influence of additional hydrophobic groups on the binding activity to the isolated human somatostatin receptors and the results are important for the design of other somatostatin analogs.

Alanine↗

PubMed1999

Synthesis and binding potencies of cyclic hexapeptide analogs of somatostatin incorporating acidic and basic peptoid residues.

The synthesis, binding affinity, and structure-activity relationships of compounds related to the cyclic hexapeptide, c[Pro6-Phe7-D-Trp8-Lys9-Thr10-Phe11], L-363,301 (the numbering in the sequence refers to the position of the residue in native somatostatin) is reported. The Pro residue in this compound is replaced with the peptoid residues Nasp [N-(2-carboxyethyl) glycine], Ndab [N-(2-aminoethyl) glycine] and Nlys [N-(4-aminobutyl) glycine]. This series of compounds enables us to draw conclusions about the influence of positively or negatively charged residues in the bridging region on the binding affinity towards the isolated human somatostatin receptors. A loss of binding to the recombinant human somatostatin (hsst) receptors in the Nasp analog compared with L-363,301 and compared with the Ndab and Nlys analogs clearly demonstrates that the presence of an acidic residue in the bridging region is unfavorable for binding to the hsst receptors. Comparison between the Ndab analog and the Nlys analog suggests that the presence of a basic residue in the bridging region might be advantageous for binding to the hsst5 receptor provided that the residue bearing the basic group extends far enough to allow for interaction with the receptor, while the length of the basic peptoid residue does not influence binding to the hsst2 receptor. These results are useful for the design of hsst5 selective somatostatin analogs.

Chromatography, High Pressure Liquid↗

PubMed1999

Association of the cell cycle transcription factor Mbp1 with the Skn7 response regulator in budding yeast.

We previously isolated the SKN7 gene in a screen designed to isolate new components of the G1-S cell cycle transcription machinery in budding yeast. We have now found that Skn7 associates with Mbp1, the DNA-binding component of the G1-S transcription factor DSC1/MBF. SKN7 and MBP1 show several genetic interactions. Skn7 overexpression is lethal and is suppressed by a mutation in MBP1. Similarly, high overexpression of Mbp1 is lethal and can be suppressed by skn7 mutations. SKN7 is also required for MBP1 function in a mutant compromised for G1-specific transcription. Gel-retardation assays indicate that Skn7 is not an integral part of MBF. However, a physical interaction between Skn7 and Mbp1 was detected using two-hybrid assays and GST pulldowns. Thus, Skn7 and Mbp1 seem to form a transcription factor independent of MBF. Genetic data suggest that this new transcription factor could be involved in the bud-emergence process.

Cell Cycle↗

PubMed1999

beta-catenin signaling can initiate feather bud development.

Intercellular signaling by a subset of Wnts is mediated by stabilization of cytoplasmic beta-catenin and its translocation to the nucleus. Immunolocalization of beta-catenin in developing chick skin reveals that this signaling pathway is active in a dynamic pattern from the earliest stages of feather bud development. Forced activation of this pathway by expression of a stabilized beta-catenin in the ectoderm results in the ectopic formation of feather buds. This construct is sufficient to induce bud formation since it does so both within presumptive feather tracts and in normally featherless regions where tract-specific signals are absent. It is also insensitive to the lateral inhibition that mediates the normal spacing of buds and can induce ectopic buds in interfollicular skin. However, additional patterning signals cooperate with this pathway to regulate gene expression within domains of stabilized beta-catenin expression. Localized activation of this pathway within the bud as it develops is required for normal morphogenesis and ectopic activation of the pathway leads to abnormally oriented buds and growths on the feather filaments. These results suggest that activation of the beta-catenin pathway initiates follicle development in embryonic skin and plays important roles in the subsequent morphogenesis of the bud.

Animals↗

PubMed1998

Structural and functional architecture of the yeast cell-cycle transcription factor swi6.

The structural and functional organisation of Swi6, a transcriptional regulator of the budding yeast cell cycle has been analysed by a combination of biochemical, biophysical and genetic methods. Limited proteolysis indicates the presence of a approximately 15 kDa N-terminal domain which is dispensable for Swi6 activity in vivo and which is separated from the rest of the molecule by an extended linker of at least 43 residues. Within the central region, a 141 residue segment that is capable of transcriptional activation encompasses a structural domain of approximately 85 residues. In turn, this is tightly associated with an adjacent 28 kDa domain containing at least four ankyrin-repeat (ANK) motifs. A second protease sensitive region connects the ANK domain to the remaining 30 kDa C-terminal portion of Swi6 which contains a second transcriptional activator and sequences required for heteromerisation with Swi4 or Mbp1. Transactivation by the activating regions of Swi6 is antagonised when either are combined with the central ankyrin repeat motifs. Hydrodynamic measurements indicate that an N-terminal 62 kDa fragment comprising the first three domains is monomeric in solution and exhibits an unusually high frictional coefficient consistent with the extended, multi-domain structure suggested by proteolytic analysis.

Ankyrins↗

PubMed1998

Stage-specific effects of sonic hedgehog expression in the epidermis.

Sonic hedgehog (Shh) is expressed in the ectoderm of the forming hair follicle and feather bud during normal development. However, inappropriate activation of the Shh signal transduction cascade in human epidermis can cause basal cell carcinoma. Here we show that during normal development of avian skin, Shh is first expressed only after the responsiveness to this protein has been suppressed in most of the surrounding ectodermal cells. Forced expression of Shh in avian skin prior to this time causes a disorganized ectodermal proliferation. However, as skin begins to differentiate, the forced expression of Shh causes feather bud formation. Subsequently, expression of Shh in interfollicular epidermis has little or no morphological effect. Restricted responsiveness to Shh in developing skin has functional consequences for morphogenesis and may have important implications for cutaneous pathologies as well.

Animals↗

PubMed1998

Design, synthesis, and biological activities of potent and selective somatostatin analogues incorporating novel peptoid residues.

We report the synthesis, bioactivity, and structure-activity relationship studies of compounds related to the Merck cyclic hexapeptide c[Pro6-Phe7-d-Trp8-Lys9-Thr10-Phe11], L-363,301 (the numbering in the sequence refers to the position of the residues in native somatostatin). The Pro residue in this compound is replaced with arylalkyl peptoid residues. We present a novel approach utilizing beta-methyl chiral substitutions to constrain the peptoid side-chain conformation. Our studies led to molecules which show potent binding and increased selectivity to the hsst2 receptor (weaker binding to the hsst3 and hsst5 receptors compared to L-363, 301). In vivo, these peptoid analogues selectively inhibit the release of growth hormone but have no effect on the inhibition of insulin. The biological assays which include binding to five recombinant human somatostatin receptors carried out in two independent laboratories and in vivo inhibition of growth hormone and insulin provide insight into the relationship between structure and biological activity of somatostatin analogues. Our results have important implications for the study of other peptide hormones and neurotransmitters.

Animals↗

PubMed1998

Regulation of the fission yeast transcription factor Pap1 by oxidative stress: requirement for the nuclear export factor Crm1 (Exportin) and the stress-activated MAP kinase Sty1/Spc1.

The fission yeast Sty1 stress-activated MAP kinase is crucial for the cellular response to a variety of stress conditions. Accordingly, sty1- cells are defective in their response to nutrient limitation, lose viability in stationary phase, and are hypersensitive to osmotic stress, oxidative stress, and UV treatment. Some of these phenotypes are caused by Sty1-dependent regulation of the Atf1 transcription factor, which controls both meiosis-specific and osmotic stress-responsive genes. However, in this report we demonstrate that the cellular response to oxidative stress and to treatment with a variety of cytotoxic agents is the result of Sty1 regulation of the Pap1 transcription factor, a bZip protein with structural and DNA binding similarities to the mammalian c-Jun protein. We show that both Sty1 and Pap1 are required for the expression of a number of genes involved in the oxidative stress response and for the expression of two genes, hba2+/bfr1+ and pmd1+, which encode energy-dependent transport proteins involved in multidrug resistance. Furthermore, we demonstrate that Pap1 is regulated by stress-dependent changes in subcellular localization. On imposition of oxidative stress, the Pap1 protein relocalizes from the cytoplasm to the nucleus in a process that is dependent on the Sty1 kinase. This relocalization is the result of regulated protein export, rather than import, and involves the Crm1 (exportin) nuclear export factor and the dcd1+/pim1+ gene that encodes an Ran nucleotide exchange factor.

Activating Transcription Factor 1↗

PubMed1998

Helios, a novel dimerization partner of Ikaros expressed in the earliest hematopoietic progenitors.

BACKGROUND: Normal hematopoietic development depends on the activity of the Ikaros transcription factor, which contains distinct zinc-finger domains that mediate DNA binding and protein dimerization. Mice homozygous for a transgene encoding a dominant-negative version of Ikaros that lacks the DNA-binding domain but not the dimerization domain have a more severe phenotype than Ikaros null mice. This observation suggests the presence of factor(s) that can dimerize with Ikaros and partially complement its function. One previously identified factor, Aiolos, probably serves this role in the lymphoid system; a related factor involved in hematopoietic progenitors remains unknown, however. RESULTS: Here, we describe the cloning of an Ikaros-related gene, Helios. Analysis of the primary sequences of Helios, Ikaros and Aiolos revealed that the DNA-binding, transcriptional activation and dimerization domains are functionally conserved. Helios activated transcription from Ikaros DNA-binding sites and could dimerize with itself, Ikaros or Aiolos. Expression of Helios was detected in the earliest hematopoietic sites of the embryo, in hematopoietic stem cells in the adult and was subsequently restricted to a subset of cells in the T cell lineage. Helios co-localized with Ikaros and Aiolos proteins in macromolecular nuclear structures and formed stable complexes in vivo with the dominant-negative version of Ikaros. CONCLUSIONS: Distinct but overlapping expression patterns of members of the Ikaros gene family during hematopoiesis might result in the formation of different multimeric complexes that have specific roles in lineage progression. The preferential expression of Helios in the earliest stages of hematopoiesis suggests that this gene functions predominantly in early progenitors.

Amino Acid Sequence↗

PubMed1998

Aiolos regulates B cell activation and maturation to effector state.

Aiolos encodes a zinc finger DNA-binding protein that is highly expressed in mature B cells and is homologous to Ikaros. In the periphery of mice homozygous for an Aiolos-null mutation, B cells exhibit an activated cell surface phenotype and undergo augmented antigen receptor (BCR)-mediated in vitro proliferative responses, even at limiting amounts of stimulant. In vivo, T cell-dependent B cell responses, including the formation of germinal centers and elevated serum IgG and IgE, are detected in Aiolos-deficient mice in the absence of immunization. Auto-antibodies and development of B cell lymphomas are frequently seen among aging Aiolos mutants. In sharp contrast to conventional B cells, B cells of the peritoneum, of the marginal zone, and the recirculating bone marrow population are greatly reduced.

Animals↗

PubMed1998

BMPs mediate lateral inhibition at successive stages in feather tract development.

The spacing of feather buds in a tract is thought to arise from the interaction between an inducing signal from the dermis and an inhibitory signal generated in the nascent buds. Local BMP-2 expression in the ectoderm precedes the formation of the ectodermal placodes, which are the first morphological sign of bud differentiation. We have altered the activity of BMP-2 or BMP-4 in the ectoderm of the feather field by expressing them or their inhibitor noggin using retroviral vectors. These experiments demonstrate that BMP-2 is necessary and sufficient to mediate the lateral inhibition that positions buds in a tract. After buds are initiated, BMP-2 and BMP-4 continue to inhibit the adoption of bud fates and help to specify the size and shape of the bud. They may do so in part by their regulation of Fgf receptor expression in both the ectoderm and dermis. Additional insights into pattern formation in the feather bud can be inferred from the effects of altered BMP activity on bud morphogenesis.

Animals↗