bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mating type and mating strategies in Neurospora
Authors: Metzenberg Robert L. , Glass N. Louise 
Published: February 2005

AbstractIn the heterothallic species Neurospora crassa, strains of opposite mating type, A and a, must interact to give the series of events resulting in fruiting body formation, meiosis, and the generation of dormant ascospores. The mating type of a strain is specified by the DNA sequence it carries in the mating type region; strains that are otherwise isogenic can mate and produce ascospores. The DNA of the A and a regions have completely dissimilar sequences. Probing DNA from strains of each mating type with labelled sequences from the A and the a regions has shown that, unlike in Saccharomyces cerevisiae, only a single copy of a mating type sequence is present in a haploid genome. The failure to switch is explainable by the physical absence of DNA sequences characteristic of the opposite mating type. While the mating type sequences must be of the opposite kind for mating to occur in the sexual cycle, two strains of opposite mating type cannot form a stable heterokaryon during vegetative growth; instead, they fuse abortively to give a heterokaryon incompatibility reaction, which results in death of the cells along the fusion line. The DNA sequences responsible for this reaction are coextensive with those sequences in the A and a regions which are necessary to initiate fruiting body formation. The genus Neurospora also includes homothallic species – ones in which a single haploid nucleus carries all the information necessary to form fruiting bodies, undergo meiosis, and produce new haploid spores. One such species, N. terricola, contains one copy each of the A and the a sequences within each haploid genome. Another homothallic species, N. africana, contains a single copy of the A sequence in the haploid genome, but does not contain any sequences corresponding to the a sequence. We present a model for the role of the mating type‐specific sequences in heterothallic and homothallic species of Neurospora and we speculate on the origin of the different modes of reproduction in the genus Neurospora.
Tumor suppressor genes
Authors: Levine Arnold J. 
Published: February 2005

AbstractThe retinoblastoma sensitivity protein (Rb) and the p53 gene product both appear to function as negative regulators of cell division or abnormal cellular growth in some differentiated cell types. Several types of cancers have been shown to be derived from cells that have extensively mutated both alleles of one or both of these genes, resulting in a loss‐of‐function mutation. In the case of the p53 gene, this mutational process appears to occur in two steps, with the first mutation at the p53 locus resulting in a trans‐dominant phenotype. The mutant p53 gene product enters into an oligomeric protein complex with the wild‐type p53 protein derived from the other normal allele and such a complex is inactive or less efficient in its negative regulation of growth control. This intermediate stage of carcinogenesis selects for the proliferation of cells with one mutant allele, enhancing the probability of obtaining a cancer cell with both alleles damaged.The DNA tumor viruses have evolved mechanisms to interact with the Rb and p53 negative regulators of cellular growth in order to enhance their own replication in growing cells. SV40 and adenovirus type 5 produce viral encoded proteins that also form oligomeric protein complexes with p53 and Rb, presumably inactivating their functions. These viral proteins are also the oncogene products of these viruses. Thus, the mechanisms by which cancer may arise in a host, via mutations or virus infections, have fundamental common pathways effecting the same cellular genes and gene products; Rb and p53.
Unbalanced transmethylation and the perturbation of the differentiated state leading to cancer
Authors: Hoffman Robert M. 
Published: February 2005

AbstractIt is proposed that the perturbation of the differentiated state in cancer is related to alterations in DNA methylation as well as to alterations in methylation of other cellular molecules, leading to an imbalance in global cellular methylation. It is hypothesized that the global imbalance in methylation is reflected in the enhanced levels of transmethylation seen in many cancer cell types as well as in a number of undermethylated molecules.
Molecular changes in carbohydrate antigens associated with cancer
Authors: Singhal Anil , Hakomori Sen‐Itiroh 
Published: February 2005

AbstractOncogenic transformation is often associated with aberrant glycosylation in experimental and human tumors. The carbohydrate epitopes, resulting either from incomplete synthesis or neosynthesis, accumulate in high density, possibly in a novel conformation, at the tumor cell surface. A variety of monoclonal antibodies have been developed that recognize tumor‐associated carbohydrate antigens and their aberrant organization at the cell surface. These carbohydrate epitopes and the antibodies specific to these structures are being exploited to develop novel diagnostic tools and therapeutic strategies for cancer.
Problems and paradigms: Chromosome reproduction: Units of DNA for segregation
Authors: Taylor J. Herbert 
Published: February 2005

AbstractEvidence is summarized which indicates that the DNA loop anchoring proteins in chromosomes are effectively heterodimers that stack and are fastened into a bilaterally symmetrical array along the chromonemal axis. The evidence consists primarily of the observations made twenty five to thirty years ago on the pattern of sister chromatid exchanges and the way the DNA chains are sorted in the formation of diplochromosomes in cells that have undergone endoreduplication. The evidence indicates that each chain of DNA in the single duplex, which is assumed to run the length of a chromosome, is anchored to a bilaterally symmetrical axis of heterodimers that sort the two original chains among the four derived chromatids of each diplochromosome in a very precise way. These observations are considered in the context of investigations on the nature of scaffold proteins and the loop anchorage sequences, as well as the advances being made on the nature of DNA binding proteins and the roles of topoisomerase II.
Yeast as a model system for understanding the control of DNA replication in eukaryotes
Authors: Bartlett Rachel , Nurse Paul 
Published: February 2005

AbstractIn the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe, the initiation of DNA replication is controlled at a point called START. At this point, the cellular environment is assessed; only if conditions are appropriate do cells traverse START, thus becoming committed to initiate DNA replication and complete the remainder of the cell cycle. The cdc2+ / CDC28+ gene, encoding the protein kinase p34, is a key element in this complex control. The identification of structural and functional homologues of p34 suggests that it has a role in the control of DNA replication in all eukaryotes. The WHI1+, CLN1+ and CLN2+ gene products, identified in S. cerevisiae, are positive regulators that function at START and may interact with p34. Determining how passing the START control point leads to the initiation of DNA replication is a major outstanding challenge in cell cycle studies.
Structure–function relationships in eukaryotic nuclei
Authors: Jackson Dean A. 
Published: February 2005

AbstractIt may be that eukaryotic nuclei contain a collection of operationally independent units (genes), each controlled through its interactions with soluble protein factors which diffuse at random throughout the nucleoplasmic space. Alternatively, nuclei might be organized in such a sophisticated fashion that specific genes, occupy distinct sites and that spatially ordered RNA synthesis, processing and transport delivers mature RNAs to predestined sites in the cytoplasm.Different fields of research support each of these extreme views. Molecular biologists inspecting the precise details of specific interactions, usually in vitro, inevitably favour the former, while cell biologists working with far more complicated systems generally assume that more elaborate arrangements exist. In considering the importance of nuclear architecture, I have attempted to relate a collection of experiments each of which intimates some close relationship between structural aspects of chromatin organization and the precise mechanisms underlying nuclear function. I will argue that higherorder structures are crucial for achieving the observed efficiency and coordination of many nuclear processes.
Selective phospholipase C activation
Authors: Wahl Matthew , Carpenter Graham 
Published: February 2005

AbstractPhospholipase C is a family of cellular proteins believed to play a significant role in the intracellular signaling mechanisms utilized by diverse hormones. One class of hormones, polypeptide growth factors, elicits its influence on cellular function through stimulation of cell surface receptor tyrosine kinase activity. Certain growth factors appear to stimulate cellular phospholipase C activity by selective, receptor‐mediated tyrosine phosphorylation of the phospholipase C‐γ1 isozyme. While the role of phospholipase C activity in growth factor regulation of cell proliferation remains to be clarified, the selective growth factor‐stimulated tyrosine phosphorylation and activation of phospholipase C‐γ1 is an interesting example of enzyme–substrate interaction at the crossroads of two important intracellular signaling pathways.
A role for interferons in early pregnancy
Authors: Roberts R. Michael 
Published: February 2005

AbstractIn order to survive, the developing conceptus must interrupt the normal ovarian cycle of the mother and extend the production of progesterone by the corpus luteum. An unusual Type 1 interferon (IFN), related structurally to the IFN–α molecule and produced in massive amounts for only a few days by the first epithelium (trophectoderm) of the preimplantation conceptus, has been implicated as the antiluteolytic agent in sheep and cattle. IFN‐a therapy during this critical period can also improve pregnancy success in sheep. It remains unclear, however, whether the trophoblast IFN have specialized biological properties or whether they are unique merely in the timing, magnitude and site of their expression.
Animal cell shape changes and gene expression
Authors: Ben‐Ze've Avri 
Published: February 2005

AbstractCell shape and cell contacts are determined by transmembrane receptor‐mediated associations of the cytoskeleton with specific extracellular matrix proteins and with ligands on the surface of adjacent cells. The cytoplasmic domains of these microfilament‐membrane associations at the adherens junction sites, also Iocalize a variety of regulatory molecules involved in signal transduction and gene regulation. The stimulation of cells with soluble polypeptide factors leads to rapid changes in cell shape and microfilament component organization. In addition, this stimulation also activates the phosphoinositide signaling pathway. Recently, a linkage between actin‐binding proteins and the phosphoinositide signaling pathway, was discovered. It is Suggested that by the association with the second messenger system, and/or by controlling the localization of regulatory molecules, the cytoskeleton may regulate gene expression.
Temporal and spatial regulation of developmentally expressed genes in Caulobacter
Authors: Gober James W. , Shapiro Lucy 
Published: February 2005

AbstractFundamental problems in developmental biology, such as the generation of asymmetry, differential transcription, and the execution of positional information, are all exhibited by a prokaryotic system, the Caulobacter cell cycle. Progeny cells resulting from each cell division have different developmental programs with respect to patterns of transcription and the initiation of DNA replication. The binary fission that yields dissimilar progeny results from asymmetry generated in the parent cell. An aspect of this fundamental developmental event is the temporally‐controlled biogenesis of a polar flagellum. Several flagellar promoters require the histone‐like protein, integration host factor (IHF) for transcription activation. IHF introduces bends in DNA resulting in the reorganization of the higher‐order structure of the promoter region. These promoters appear to be transcribed from the chromosome in the swarmer pole of the predivisional cell. The newly replicated chromosomes in the predivisional cell differ in sedimentation coefficient and in the ability to initiate replication in the progeny cell. We hypothesize that the differential higher order structure of the two chromosomes contributes to both replication potential and transcription specificity.
Stabilization and post‐translational modification of microtubules during cellular morphogenesis
Authors: Bulinski Jeannette C. , Gundersen Gregg G. 
Published: February 2005

AbstractThis review discusses the possible role of α‐tubulin detyrosination, a reversible post‐translational modification that occurs at the protein's C‐terminus, in cellular morphogenesis. Higher eukaryotic cells possess a cyclic post‐translational mechanism by which dynamic microtubules are differentiated from their more stable counterparts; a tubulin‐specific carboxypeptidase detyrosinates tubulin protomers within microtubules, while the reverse reaction, tyrosination, is performed on the soluble protomer by a second tubulin‐specific enzyme, tubulin tyrosine ligase. In general, the turnover of microtubules in undifferentiated, proliferating cells is so rapid that the microtubules accumulate very little detyrosinated tubulin; that is, they are enriched in tyrosinated tubulin. However, an early event common to at least three well‐studied morphogenetic events myogenesis, neuritogenesis, and directed cell motility is the elaboration of a polarized array of stable microtubules that become enriched in detyrosinated tubulin. The formation of this specialized array of microtubules in specific locations in cells undergoing morphogenesis suggests that it plays an important role in generating cellular asymmetries.
Control of metamorphosis and pattern formation in Hydratinia (hydrozoa, cnidaria)
Authors: Berking Stefan 
Published: February 2005

AbstractHydractinia echinata is a marine colonial hydroid, a relative of the more widely known Hydra. In contrast to Hydra, embryogenesis, metamorphosis and colony growth in Hydractinia are experimentally accessible and therefore, provide an ideal model system for investigating the biochemical basis of pattern formation. In particular, the processes involved in the transformation of the drop‐shaped freely swimming larva into a sessile tube‐shaped polyp are easily monitored, because this transfomation can be induced by application of various substances. Our results indicate that the internal level of S‐adenosylmethionine (SAM), potentially the most important methyl donor in transmethylation processes, plays a key role in the onset of metamorphosis. It is also proposed that the internal level of SAM plays a pivotal role in the proportioning and spacing of polyps within the colony.
Immune defense and suppression in insects
Authors: Schmidt Otto , Theopold Ulrich 
Published: February 2005

AbstractInsect endoparasitoids are able to circumvent the defense reactions of their habitual hosts. In a hymenopteran wasp species, virus‐like particles, found on the egg surface are responsible for the protection against the encapsulation reaction of the host caterpillar. Some of the particle proteins are structurally and probably functionally related to host protein(s). Biological properties of some of the host proteins suggest that they might be involved in the insect defense reaction.
Late events in regulated exocytosis
Authors: Tatham Peter E. R. , Gomperts Bastien D. 
Published: February 2005

AbstractTo understand the intracellular mechanisms that control exocytosis it is necessary to have access to the cell interior. This is achieved by plasma membrane permeabilisation or by application of patch‐pipettes. These conditions permit control over the cytosol composition and also allow leakage of soluble factors that may have roles in the exocytotic mechanism. Different permeabilisation methods allow different extents of leakage and therefore provide complementary data. The exocytotic machinery itself remains intact and can be activated by providing Ca2+ and/or a guanine nucleotide. In some cells there is evidence for the participation of two guanine nucleotide‐binding proteins (Gp and GE), as well as a Ca2+ ‐binding protein. In others Ca2+ is the only requirement. In a number of cell types, ATP is not required for the late steps in the secretory pathway.
The helix‐loop‐helix domain: A common motif for bristles, muscles and sex
Authors: Garrell Joan , Campuzano Sonsoles 
Published: February 2005

AbstractThree apparently unrelated developmental processes – mammalian myogenesis, the choice of neural fate and sex determination in Drosophila – are controlled by a common mechanism. Most of the genes governing these processes encode transcriptional factors that contain the helix‐loop‐helix (HLH) motif. This domain mediates the formation of homo‐ or heterodimers that specifically bind to DNA through a conserved basic region adjacent to the HLH motif. Dimers differ in their affinity for DNA and in their ability to activate transcription from HLH binding‐site containing promoters. In addition, the activity of HLH proteins is inhibited by dimerization with another class of HLH proteins that lack a basic domain entirely or have an altered one. These structural properties provide a molecular mechanism to explain the synergistic and antagonistic functional relations among the HLH encoding genes that control several developmental pathways.
Role of colony stimulating factor‐1 (CSF‐1) and other lympho‐hematopoietic growth factors in mouse pre‐implantation development
Authors: Pampfer Serge , Arceci Robert J. , Pollard Jeffrey W. 
Published: February 2005

AbstractMouse pre‐implantation development appears to be under the control of paracrine and autocrine growth factors. The epithelium of the oviduct and the uterus together, with the population of macrophages and lymphocytes present in the reproductive tract from the onset of pregnancy, are thought to be the major sources of paracrine growth factors targeted to the developing embryos. Some of the growth factors are synthesized by both uterine epithelial cells and activated lympho‐hematopoietic cells, suggesting a partial overlap of the regulatory signals used by the reproductive and lympho‐hematopoietic systems. Such growth factors may be the long sought‐after mediators of the synchrony between the pre‐implantation embryo and the sex‐steroid hormone‐induced changes in the uterus.
Chemosensory behaviour of Tetrahymena
Authors: And Vegn Leick , Hellung‐Larsen Per 
Published: February 2005

AbstractFree swimming cells of the ciliated protozoan Tetrahymena are attracted to certain chemicals by chemokinesis. However, a special type of chemotaxis in response to a chemical gradient is found in cells gliding very slowly in semisolid media. In contrast to classical chemotaxis by leukocytes, which is solely positive towards chemo‐attractants, the oriented chemokinesis by gliding Tetrahymena involves both positive and negative elements. The major chemo‐attractants are peptides and/or proteins, and they may be compounds which signal the presence of food in the natural environment of this freshwater phagotroph.
Molecular components of the mitotic spindle
Authors: Kuriyama Ryoko , Nislow Corey 
Published: February 2005

AbstractMitotic spindles constitute the machinery responsible for equidistribution of the genetic material into each daughter cell during cell division. They are transient and hence quite labile structures, changing their morphology even while performing their function. Biochemical, immunological and genetic analyses of mitotic cells have allowed us to identify a variety of molecules that are recruited to form the spindle at the onset of mitosis. Evaluation of the roles of these molecules in both the formation and in the dynamics of spindle microtubules should be important for understanding the molecular basis of mitosis and its regulation. We have recently identified a novel mitosis‐specific microtubule‐associated protein (MAP) using a monoclonal antibody probe raised against the mitotic spindles isolated from cultured mammalian cells. This 95/105 kDa antigen represents a unique component of the spindle distinct from any of the other MAPs reported so far. Antibody microinjection resulted in mitotic inhibition in a stage‐specific and dosedependent manner, indicating that the protein is an essential spindle component.
Regulation of meiotic maturation in the mammalian oocyte: Inteplay between exogenous cues and the microtubule cytoskeleton
Authors: Albertini David F. 
Published: February 2005

AbstractMammalian oocytes exhibit a series of cell cycle transitions that coordinate the penultimate events of meiosis with the onset of embryogenesis at fertilization. The execution of these cell cycle transitions, at G2/M of meiosis‐I and metaphase/anaphase of meiosis I and II, involve both biosynthetic and post‐translational modifications that directly modulate centrosome and microtubule behavior. Specifically, somatic cells alter the signal transduction pathways in the oocyte and influence the expression of maturation promoting factor (MPF) and cytostatic factor (CSF) activity through a microtubule‐dependent mechanism. The regulation of the oocytes' cell cycle machinery by hormone‐mediated somatic cell signals, involving both positive and negative stimuli, ensures that meiotic cell cycle progression is synchronized with the earliest pivotal events of mammalian reproduction.
Sorting of proteins to the vacuoles of plant cells
Authors: Vitale Alessandro , Chrispeels Maarten J. 
Published: February 2005

AbstractThe secretory system of plant cells sorts a large number of soluble proteins that either are secreted or accumulate in vacuoles. Secretion is a bulk‐flow process that requires no information beyond the presence of a signal peptide necessary to enter the endoplasmic reticulum. Many vacuolar proteins are glycoproteins and the glycans are often modified as the proteins pass through the Golgi complex. Vacuolar targeting information is not contained in glycans as it is in animal cells; rather, targeting information is in polypeptide domains as it is in yeast cells. Several such domains have now been identified, but these show little or no amino acid sequence homology. We discuss the possibilities that targeting of protein to plant vacuoles may involve receptors as well as aggregation of protein at low pH.
Control of transcription of Drosophila retrotransposons
Authors: Arkhipova Irina R. , Ilyin Yurii V. 
Published: February 2005

AbstractStudies of transcriptional control sequences responsible for regulated and basal‐level RNA synthesis from promoters of Drosophila melanogaster retrotransposons reveal novel aspects of gene regulation and lead to identification of trans‐acting factors that can be involved in RNA polymerase II transcription not only of retrotransposons, but of many other cellular genes. Comparisons between promoters of retrotransposons and some other Drosophila genes demonstrate that there is a greater variety in basal promoter structure than previously thought and that many promoters may contain essential sequences downstream from the RNA start site.