bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural and functional characterization of genes encoding Dictyostelium prestalk and prespore cell‐specific proteins
Authors: Early Anne , McRobbie Stuart J. , Duffy Karen T. , Jermyn Keith A. , Tilly Rita , Ceccarelli Adriano , Williams Jeffrey G. 
Published: May 2005

AbstractThe nucleotide sequence of D19, a Dictyostelium gene that encodes a prespore‐specific mRNA sequence shows it to encode PsA, the cell surface protein detected by the MUD 1 monoclonal antibody. The predicted sequence of the protein reveals a largely hydrophobic C terminus, with chemical similarity to proteins known to be attached to the plasma membrane via a phosphatidylinositol link. The C‐terminal region has direct sequence homology to the contact sites A protein and to the phosphatidylinositol‐linked form of a chicken N‐CAM, suggesting that it might play a role in cell adhesion. Expression of the D19 gene is known to be induced by cAMP and repressed by adenosine. The accumulation of the D19 mRNA is also repressed by DIF, the putative stalk‐specific morphogen, and this effect is mediated at the transcriptional level. The pDd56 and pDd63 genes are induced by DIF, and they are specific markers of prestalk and stalk cells. They encode, respectively, ST310 and ST430, two proteins that were first identified by two‐dimensional gel electrophoresis. Both proteins are predominantly composed of a highly conserved, 24‐amino acid repeat. The two proteins are localized in the slime sheath of the migratory slug and in the stalk tube and stalk cell wall of the mature culminant, where they presumably function as structural components of the extracellular matrix. We have constructed marked derivatives of the pDd56, pDd63, and D19 genes, and these are correctly regulated after transformation into Dictyostelium cells. Thus we have determined the structure, and elucidated possible functions, for one prespore and two prestalk genes. These sequences should be of value, both as markers of the earliest events in cellular differentiation and in identifying the regulatory sequences controlling cell type‐specific gene expression.
Regulation of mRNA stability and the poly(A) problem in Dictyostelium discoideum
Authors: Manrow Richard E. , Shapiro Robert A. , Herrick David , Steel Laura F. , Blinder Dmitry , Jacobson Allan 
Published: May 2005

AbstractThis paper reviews our studies of three aspects of post‐transcriptional regulation in Dictyostelium discoideum: (1) the determinants of mRNA stability in vegetative amoebae; (2) the effects of disaggregation and cyclic AMP on the decay rates of cell‐type‐specific mRNAs in late developing cells; and (3) the cytoplasmic function of the 3′ poly(A) tracts present on most mRNAs. We find that: (1) mRNA stability in vegetative amoebae is not dependent on mRNA size, ribosome loading, or poly(A) tract length, but may be determined by specific 3′‐untranslated sequences within a given mRNA; (2) mRNA decay rates in late developing cells are heterogeneous, and cyclic AMP does not act directly to stabilize cell‐type‐specific mRNAs; and (3) poly(A) is most likely involved in the initiation of protein synthesis via an interaction with cytoplasmic poly(A)‐binding proteins.
Post‐transcriptional regulation of ribosomal protein gene expression during development in Dictyostelium discoideum
Authors: Steel Laura F. , Jacobson Allan 
Published: May 2005

AbstractWe have isolated recombinant plasmids that contain cDNA inserts complementary to mRNAs encoding six different r‐proteins of Dictyostelium discoideum. Southern and quantitative dot blot analyses have shown that each of the r‐protein genes represented in these plasmids is encoded by a single copy gene and that these genes are not tightly linked to each other. We have determined the relative amount of the six r‐protein mRNAs present in cells at intervals throughout development and find that for the first 9 hours of development, each of the mRNAs remains present at virtually the same level as in vegetatively growing cells. Between 9 and 11 hours of development, there is a rapid loss of these mRNAs to 15% or less of vegetative levels, and that low level remains, or slightly declines, through the late stages of development. We have shown that two post‐transcriptional events contribute to the developmental regulation of the expression of the r‐protein genes. The first involves a specific block to translational initiation that is not the result of inactivation of these mRNAs by decapping or deadenylation. The second is a change in the stability of these mRNAs during early development. In order to begin to analyze the role of specific sequences that may act as targets or signals in these events, we have cloned and sequenced a 1.9‐kb genomic DNA fragment that encodes one of the r‐proteins. We find that transcription of this gene begins in a pyrimidine‐rich region that is not preceded by a TATA box, the gene contains a single intron of 350 bp, and there are two alternative 3′ processing sites. In addition, the 5′‐untranslated region of the transcript contains an unusually high percentage of G and C residues relative to other Dictyostelium mRNAs.
DNA repair in Dictyostelium
Authors: Deering Reginald A. 
Published: May 2005

AbstractRecent approaches to the study of DNA repair in Dictyostelium discoideum are reviewed. Thymidine auxotrophs facilitate the uptake of labeled thymidine into DNA during its replication and repair. The tmpA 600 mutation leads to a loss of thymidylate synthase activity, and tdrA600 results in increased transport of thymidine into the cell. In the HPS401 double mutant (tmpA600tdrA600), thymidine is taken up uniformly into the nuclear and mitochondrial DNAs at levels up to 50‐fold that in the wild type. tmpA maps on linkage group III. tdrA is on IV or VI, which cosegregate in strains containing this mutation. Alkaline sucrose gradients of nuclei from HPS401 pulsed for 15 min with [3H]thymidine in axenic medium show that the initially labeled single‐strand DNA is about 7 × 106 daltons, which may be the size of the replicon. This nascent DNA matures in about 45 minutes to 2 × 108 daltons. Ultraviolet light (254 nm) decreases the size of the nascent DNA and delays its maturation. In addition to studies of DNA repair utilizing repairproficient and ‐deficient mutants of thymidine auxotrophs, we are currently using two approaches for cloning genes involved in repair: (1) genes are sought that can functionally complement repair defects in Saccharomyces cerevisiae following transformation with a D. discoideum DNA library in YEp 24(URA); 4‐NQO is used for the selection of RAD transformants; and (2) we have characterized and purified to near‐homogeneity two repair enzymes from D. discoideum–uracil‐DNA glycosylase and AP‐endonuclease. An Nterminal sequence has been determined for the glycosylase, and a synthetic oligonucleotide probe derived from this sequence will be used to screen for this gene. A similar approach is in progress for the AP‐endonuclease.
Electron microscopic localization of myosin II and ABP‐120 in the cortical actin matrix of Dictyostelium amoebae using IgG‐gold conjugates
Authors: Ogihara S. , Carboni J. , Condeelis J. 
Published: May 2005

AbstractTo narrow the field of possible functions of an actin‐binding protein (ABP‐120) and myosin II, we have used high resolution immunocytochemistry with IgG‐colloidal gold conjugates to identify the types of actin containing structures with which these proteins are associated in the isolated cell cortex. Staining for myosin II and ABP‐120 is associated with distinct regions of the actin cytoskeleton in isolated cortices. Myosin II is localized to lateral arrays of filaments, where it is clustered and has a density that is unrelated to distance from the plasma membrane. Staining for myosin II is associated also with unidentified cytoplasmic vesicles. However, staining for ABP‐120 is concentrated in dense networks of branched microfilaments that are adjacent to the plasma membrane or in surface projections (residual pseudopods and lamellopods). These results are consistent with a role for ABP‐120 in the formation of filament networks in vivo and further suggest that networks of branched microfilaments are unlikely to participate in motility that is mediated by myosin II.
Movement of the Dictyostelium discoideum slug: Models, musings, and images
Authors: Breen Edmond J. , Williams Keith L. 
Published: May 2005

AbstractThe last 5 years have resulted in many advances in knowledge of the cytoskeleton and motility of individual cells. Here the problem of multicellular movement is addressed. The Dictyostelium discoideum slug is examined, and models for how approximately 100,000 cells become coordinated to move are briefly reviewed. Experiments that contributed to model building as well as those used to test models are considered. Four levels of experimentation are considered: (1) the extracellular matrix (ECM) is examined as a component of the system; (2) information obtained by examining the organisation of slug cells through sectioning is presented; (3) time, the 4th dimension, is considered, and approaches to studying the dynamics of cell interactions from the point of view of movement are outlined, and (4) cell adhesion molecules are addressed.
Cell‐cell adhesion in Dictyostelium discoideum
Authors: Loomis William F. 
Published: May 2005

AbstractThree separate mechanisms of cell‐cell adhesion have been shown to appear at different stages of development in Dictyostelium discoideum. During the first few hours of development, the cells synthesize and accumulate a glycoprotein of 24,000 daltons (gp24) that is positioned in the membrane. The time of appearance of gp24 correlates exactly with the time of appearance of cell‐cell adhesion in two strains in which temporal control varies by several hours. Antibodies specific to gp24 are able to block cell‐cell adhesion during the first few hours of development but not during later development. By 8 hr of development, another glycoprotein, gp80, that is not recognized by antibodies to gp24 accumulates on the surface of cells. This membrane protein mediates an independent adhesion mechanism during the aggregation stage that is resistant to 10 mM EDTA. Antibodies specific to gp80 can block EDTA‐resistant adhesion during this stage. During subsequent development, gp80 is removed from the cell surface and replaced by another adhesion mechanism that is insensitive to antibodies to either gp24 or gp80.A λgtll expression vector carrying a Dictyostelium cDNA insert was isolated that directs the synthesis of a fusion protein recognized by antibodies specific to gp24. This cDNA was used to probe a genomic library. A clone carrying a 1.4‐kb insert of genomic DNA was recognized by the cDNA and shown to hybridize to a 0.7‐kb mRNA that accumulates early in development. This unusually small RNA could code for the small protein, gp24. Southern analysis of restriction fragments generated by various enzymes on Dictyostelium DNA with both the cDNA and genomic clones indicated the presence of two tandem copies of the gene. This may account for the failure to recover mutations resulting in the lack of gp24.Mutations have been recovered that result in the lack of accumulation of gp80, and cells carrying these mutations have been shown to be missing the second adhesion mechanism. These mutant strains are able to complete development because the other adhesion mechanisms are not impaired. Sequential addition of adhesion mechanisms provides a means for the formation of multicellular organisms from previously solitary cells.
Biosynthesis of 117 antigen: A cell cohesion molecule in Dictyostelium discoideum
Authors: Sadeghi Homayoun , Silva Aline Da , Klein Claudette 
Published: May 2005

Abstract117 antigen is involved in the process of intercellular cohesiion in Dictyostelium discoideum [Brodie et al., 1983]. The antigen, a 69‐and 72‐kDa doublet, was found to arise from a 60‐and 62‐kDa precursor. The mature antigen contains N‐linked oligosaccharides that are sulfated and fucosylated [Sadeghi et al., 1987]. These oligosaccharide chains are resistant to endoglycosidase H digestion. 117 antigen also contains a post‐translationally added carbohydrate‐containing modification(s). Unlike the N‐linked oligosaccharide, this carbohydrate moiety is sensitive to periodate oxidation. 117 antigen is developmentally regulated, and the changes in rate of 117 antigen synthesis reflect changes in the cellular levels of its mRNA. 117 mRNA accumulates in starving cells and reaches its maximum when cells become aggregation competent. The mRNA levels then decline, and by the time the slug structure is formed, no 117 mRNA is present. 117 mRNA reaccumulates for a brief period during early culmination and then returns to an undetectable level.
Cell behavior during formation of prestalk/prespore pattern in submerged agglomerates of Dictyostelium discoideum
Authors: Takeuchi Ikuo , Kakutani Tetsuji , Tasaka Masao 
Published: May 2005

AbstractWhen cells dissociated from Dictyostelium discoideum slugs were cultured in roller tubes, they formed agglomerates in which prestalk cells were initially dispersed but soon sorted out to the center and then moved to the edge to reconstitute the prestalk/prespore pattern. To examine the mechanism of sorting out, individual prestalk cells were traced by a videotape recorder. The radial component of the rate of movement toward the center of the presumptive prestalk region was calculated. Prestalk cells did not move randomly, but rather directionally toward the center. Thei movement was pulsatile, with a period of ca. 15 min, and accompanied by occasional formation of cell streams, thus resembling the movement observable during cell aggregation. These results favor the idea that prestalk cells sort out to the prestalk region due to differential chemotaxis rather than differential adhesiveness. After formation of the prestalk/prespore pattern, the prestalk region rotated along the circumference of the agglomerates. This appears comparable to migration of slugs on the substratum, the rate of rotation being similar to that of slug migration.To examine the processes of pattern formation during development. washed vegetative cells were cultured in roller tubes. Prespore cells identified by antispore immunoglobulin initially appeared randomly within the agglomerates, but then nonprespore cells accumulated in the center and finally moved to the edge to establish the prestalk/prespore pattern, the processes being similar to those of pattern reconstruction with differentiated prestalk and prespore cells.
A mutant strain of Polysphondylium with defects in many genes
Authors: Francis David , Shaffer Arthur 
Published: May 2005

AbstractPN6024 is a mutant strain of P. pallidum which appeared on selection for resistance to MDMP, an inhibitor of translation. It was found to be mutant in four other traits, being resistant to tubercidin, incapable of growth at 31.5°C, abnormal in development, and slow growing at 25°C. Genetic crosses using the macrocyst cycle showed that these five traits are controlled by five unlinked genes. The hypothesis is that movement of a transposon to multiple new locations caused these mutations. A difference in restriction fragment pattern between PN6024 and its parent PN600 support the hypothesis. Attempts were made to find conditions generating other strains like PN6024. Selection for growth in the presence of tubercidin yielded clones which resemble PN6024 in being developmentally abnormal as well as tubercidin resistant. Tubercidin treatment also increased the frequency of clones resistant to canavanine. It is suggested that tubercidin is mutagenic because it causes movement of the putative transposon, not because it generates point mutations. Growth under conditions of stress (at 31.5°C, at 8°C, in the presence of 2% ethanol) had at most an erratic effect in generating strains like PN6024.Three substrains appeared spontaneously in cultures of PN6024. These differed in developmental characteristics from each other and from the parent strain. It is suggested that they carry mutations in genes which control the choices between growth and aggregation, and between aggregation and encystment.
Ammonia can stimulate or inhibit aggregate density in Dictyostelium mucoroides: A quantitative test of the hypothesis that ammonia is the aggregation‐suppressing gas
Authors: Feit Ira N. 
Published: May 2005

AbstractAmmonia, at moderate concentrations, stimulates aggregate density of Dictyostelium mucoroides. The range of stimulatory concentrations includes ammonia concentrations established by populations of amebae. At higher concentrations, ammonia inhibits aggregate density.A quantitative test of the hypothesis that ammonia is the aggregation‐suppressing gas has been carried out. The concentration of ammonia established over defined populations of amebae is one or two orders of magnitude lower than the concentration of ammonia required to exert the same degree of inhibitory effect as the populations of amebae exert.An additional difference between ammonia and the aggregation‐suppressing gas is the fact that increasing concentrations of the aggregation‐suppressing gas cause progressively larger aggregation streams, while increasing concentrations of ammonia have no such effect.The stimulatory effect of ammonia at concentrations established by ameba populations indicates that ammonia must be included in the variables affecting the aggregation process and that this ammonia effect must be taken into account in any quantitative modelling of the aggregation process.
Purification, characterization, and partial structure of D factor from Polysphondylium violaceum
Authors: Hanna Michael H. , Fatone Michael , Newth‐Clark Cynthia , Salerno John , Clemans Steven 
Published: May 2005

AbstractThe A component of D factor (DfA) was overproduced during development of wild type Polyspondylium violaceum strain China after starvation in liquid medium. Crude DfA excreted by strain China was partially purified by ultrafiltration using Amicon YM10 and YM2 filters with DfA extracted from the filtrate by absorption onto a preparative grade C‐18 resin. The concentrated material was further purified on a C‐18 analytical column using both acetonitrile:water and methanol: water gradients. This highly purified fraction was a single component with a final specific activity of greater than 106 units per mg dry weight. Purified DfA is red having a broad visible absorbance at 500 nm and a ultraviolet (uv) absorbance at 290–300 nm. The red chromophore is sensitive to pH and to oxidation‐reduction. 1H and 13C nmr studies with purified DfA indicate that it is a C11 compound with both polar and non‐polar regions. The non‐polar region has been identified as a hexanone and is the same as the side chain of DIF from Dictyostelium discoideum. Purified DfA has been used in studies with the D factor non‐producing mutant, tsg‐119 cyc‐1 aggA586 (A586), to show that neither production of glorin nor chemotactic sensitivity to glorin are affected by D factor. However, founder cells develop in A586 mutant populations only after addition of D factor. These data suggest that DfA may be necessary for induction of aggregate formation by aggregation‐competent amoebae.
Cell size in Dictyostelium
Authors: Waddell David R. 
Published: May 2005

AbstractCellular slime mold amoebae have become a model system for the study of cell motility and the cytoskeleton. A basic problem which all cells face that involves the cytoskeleton is how to control their size. The varied ways in which cellular slime mold amoebae change their cell size‐by changing the size at which division occurs, by cell fusion, and by control over cytokinesis‐are reviewed. A model is presented which attempts to explain how the mechanisms affected in certain cytokinesis mutants in Dictyostelium discideum known as phg mutants could be involved in control of cell size in the predatory slime mold Dictyostelium caveatum.
Changes in protein synthetic activity in early Drosophila embryos mutat for the segmentation gene Krüppel
Authors: Bedian Vahe , Summers Michael C. , Kauffman Stuart A. 
Published: May 2005

AbstractWe have identified early embryo proteins related to the segmentation gene Krüppel by [35S]methionine pulse labelling and two‐dimensional gel electrophoresis. Protein synthesis differences shared by homozygous embryos of two Krüppel alleles when compared to heterozygous and wild‐type embryos are reported. The study was extended to syncytial blastoderm stages by pulse labelling and gel analysis of single embryos, using Krüppel specific proteins from gastrula stages as molecular markers for identifying homozygous Krüppel embryos. Localized expression of interesting proteins was examined in embryo fragments. The earliest differences detected at nuclear migration stages showed unregulated synthesis in mutant embryos of two proteins that have stage specific synthesis in normal embryos. At the cellular blastoderm stage one protein was not synthesized and two proteins showed apparent shifts in isoelectric point in mutant embryos. Differences observed in older embryos included additional proteins with shifted isoelectric points and a number of qualitative and quantitative changes in protein synthesis. Five of the proteins with altered rates of synthesis in mutant embryos showed localized synthesis in normal embryos. The early effects observed are consistent with the hypothesis that the Krüppel product can be a negative or positive regulator of expression of other loci, while blastoderm and gastrula stage shifts in isoelectric point indicate that a secondary effect of Krüppel function may involve post‐translational modification of proteins.
Pretranslational control of the levels of glyoxysomal protein gene expression by the embryonic axis in maize
Authors: Skadsen Ronald W. , Scandalios John G. 
Published: May 2005

AbstractPrevious studies showed that the expression of catalase‐2 (CAT‐2) and other glyoxysomal proteins is independently controlled in the scutella of intact maize seedlings. In this study, removal of the embryonic axis prior to seed imbibition dramatically decreased the amounts of all but two of the 19 immunologically detectable glyoxysomal proteins in the scutellum, including CAT‐2. The temporal expression profile of CAT‐2 was also altered. Removal of the axis after seeds were fully imbibed (24 hr) had little effect on the subsequent pattern of expression of CAT‐2. The effect of axis removal was specific for glyoxysomal enzymes and caused relatively little change in the population of stainable scutellar proteins. In vitro translation studies and nucleic acid hybridization with a gene‐specific cloned probe (for Cat2) revealed that the mRNA levels for glyoxysomal proteins were sharply lowered by axis removal. This study provides evidence that a signal may be released from the embryonic axis during imbibition, leading to the expression of a set of glyoxysomal enzymes by enhancing either the transcription of their genes or transcript stability.
Effects of heat shock on protein processing and turnover in developing Drosophila wings
Authors: Petersen Nancy S. , Young Patricia 
Published: May 2005

AbstractDevelopmental defects called phenocopies can be induced by heating Drosophila melanogaster pupae at specific developmental stages. The induction of the defects is thought to be a result of interference with gene expression at some level (Petersen and Mitchell, Dev Biol 1987; 121:335‐341, 1987). Here we look at protein turnover in developing 52‐hour wings and at the effect of heat on the proteolytic processing of three proteins that normally turn over rapidly. The effect of the heat treatment itself on the turnover of each protein is different. However, all of the proteins appear to be stabilized at 25°C during recovery from severe heat shocks.