bluuebunny/crossref_metadata_2025 huggingface dataset:
Hormonal and heat‐stress regulation of protein synthesis in the aleurone layers of barley seeds
Authors: Brown Peter H. , Brodl Mark R.
Published: February 2005

Barley aleurone cells have long served as a model system for studying the regulation of gene expression in plants. In this review we survey what is known about hormone‐regulated gene expression in aleurone cells. We also describe the effects of heat stress on gene expression in this system, and speculate how the aleurone cell prioritizes its response between hormone‐induced and environment‐induced programs of gene expression.
The banting and best department of medical research at the university of toronto
Authors: Fritz Irving B.
Published: February 2005

Places is a Features column presenting descriptions of and reports on major research institutes in biology. Previous articles have dealt with, amongst other institutions, the Imperial Cancer Research Fund, the Marine Biological Laboratory at Woods Hole, the John Innes Institute, and the Department of Embryology of the Carnegie Institute. In the following article, Irving B. Fritz reviews the history and present program of one of Canada's outstanding institutions, the Banting and Best Department of Medical Research of the University of Toronto.
Structure of human serum cholinesterase
Authors: Lockridge Oksana
Published: February 2005

Human cholinesterase has recently been sequenced and cloned. It is a glycoprotein of 4 identical subunits, each subunit containing 9 carbohydrate chains and 3.5 disulfide bonds. Protein folding is likely to be very similar in human cholinesterase and Torpedo acetylcholinesterase. The cholinesterases have no significant sequence homology with the serine proteases and seem to belong to a separate serine esterase family.
Chromatin organization at meiosis
Authors: Møens Peter B. , Pearlman Ronald E.
Published: February 2005

From 1956, when the complex ultrastructure of meiotic chromosomes was discovered, 1 until 1985, when the isolation of meiotic chromosome cores was reported, knowledge of the molecular structure of the meiotic chromosome was at best a dream. The dissection of meiotic chromosome structures has become a realistic challenge through the arrival of isolated symptonemal complexes (SCs), monoclonal and polyclonal antibodies against SCs, the possibility for screening expression libraries for genes that encode SC proteins, the isolation of SC‐associated DNA, and the development of techniques for the in situ recognition of DNA sequences in the context of the meiotic chromosome structure.
Modulation of myosin assembly
Authors: Epstein Henry F.
Published: February 2005

Myosin self‐assembly is generally considered to be the major process in thick filament formation within striated muscles. The biological assembly of myosin into thick filaments is being analysed by genetic dissection as well as biochemical and morphological experiments in the nematode Caenorhabditis elegans. This work shows that the assembly of myosin is modulated by its biosynthesis and interaction with non‐myosin proteins. Assemblages which generate multiple nascent thick filaments may play a central role in a catalytic cycle of myosin assembly.
Mechanism of Mu DNA transposition
Authors: Chaconas George , Surette Michael G.
Published: February 2005

The study of Mu DNA transposition in vitro has resulted in a much better understanding of the biochemical details of the transposition process. An early step in transposition is the generation of a 5th structure which is the product of the strand‐tansfer reaction. The polarity of the strand transfer has been determined and substantial progress has been made on the role of the individual proteins. Moreover, the strand‐transfer reaction is mediated by stable protein–DNA complexes, or transposomes, and the reaction can be divided into two sequential steps. The role of the transposomes and the requirement for a supercoiled Mu DNA substrate are also discussed.
Amphibian metamorphosis: An immunologic opportunity!
Authors: Ruben Laurens N. , Clothier Richard H. , Balls Michael , Horton John D.
Published: February 2005

Anuran amphibian metamorphosis is an immunologically interesting period. For the investigator, it provides an unusual opportunity for analyzing both humoral regulation of the immune response and the development and maintenance of self‐tolerance. Some of the questions one can ask are: Why don't immunocompetent larvae destroy antigenically disparate adult cells as they differentiate within them during metamorphosis? Do the dramatic hormonal changes occurring during this period regulate immunological function? How do animals in metamophorsis protect themselves from their immunologically hostile environment?
Specific protein changes during memory acquisition and storage
Authors: Nelson Thomas J. , Alkon Daniel L.
Published: February 2005

Changes in several distinct types of neuronal proteins are now known to be associated with learning. In this review, we will summarize the properties of these proteins and relate these properties to prominent theories of the biochemical basis of memory.
Cytoplasmic determination and distribution of developmental potential in the embryo of Caenorhabditis elegans
Authors: Schierenberg Einhard
Published: February 2005

Development of the nematode Caenorhabditis elegans has been described completely on a cell‐by‐cell basis. In an invariant pattern five somatic founder cells and the primordial germ cell are generated within the first hour after the onset of cleavage. Using a laser microbeam for manipulation of individual blastomers several aspects of early embryogenesis have been investigated, including the expression of cellular polarity, the localization of lineage‐specific cleavage potential, the necessity for early cell–cell interaction, and the control of differential cell‐cycle timing. The experiments demonstrate the central importance of a correct partitioning of cytoplasmic components during early embryogenesis and suggest a stepwise, binary segregation mechanism associated with the unequal cleavages in the germline.
Regulation of the Ca2+ pump atpase by cAMP‐dependent phosphorylation of phospholamban
Authors: Tada Michihiko , Kadoma Masaaki
Published: February 2005

Ca2+ transients in myocardial cells are modulated by cyclic AMP‐dependent phosphorylation of a protein in the sarcoplasmic reticulum. This protein, termed phospholamban, serves to regulate the Ca2+ pump ATPase of this membrane, thus altering the mode of Ca2+ transients and the myocardial contractile response. Elucidating the structure of phospholamban and its intimate interaction with the Ca2+ pump ATPase should provide the basis for understanding, at the molecular level, how the cAMP system contributes to excitation‐contraction coupling in muscle cells.
Bacterial cell walls and membranes. Discovery of the teichoic acids
Authors: Baddiley James
Published: February 2005

Teichoic acids are major wall components of most Gram‐positive bacteria. Their discovery followed that of their nucleotide precursors. Lipoteichoic acids associated with the cell membrane were discovered at the same time. Events leading to these discoveries and the probable function of teichoic acids in cation control are described.
Estrogens, antiestrogens and cell proliferation
Authors: Kon Oi Lian
Published: February 2005

The classical estrogen receptor model does not sufficiently account for the tumor‐promoting activity of extrogens or for the antiproliferative effect of antiestrogens in estrogen‐dependent tumors. Particular difficulties not readily accommodated within the model are that hormonal autonomy can supervene without loss of the estrogen receptor and that antiestrogen effects are highly context‐dependent, without apparent differences in the estrogen receptor itself or in metabolic transformation of antiestrogens. Recent studies suggest that estrogens may promote cell proliferation, in part, through the mediation of growth factors and that antiestrogens may exert some of their effects by mechanisms unrelated to the estrogen receptor.
Essential roles of 70kDa heat inducible proteins
Authors: Craig Elizabeth A.
Published: February 2005

The 70kDa heat inducible proteins (hsp70s) are a highly conserved family of proteins found in every organism examined. Some hsp70 proteins are essential for cell viability. Recent work has revealed that these proteins are involved in the movement of proteins into and through various compartments of the eukaryotic cell.
The discovery of gene amplification in mammalian cells: To be in the right place at the right time
Authors: Schimke Robert T.
Published: February 2005

The constancy of the genome structure of an organism has been accepted dogma for a number of decades. The genetic variegation of maize as described by McClintock in the 1940s and subsequently shown to be mediated by transposable elements indicated a degree of genomic fluidity not appreciated previously. The discovery of gene amplification in somatic mammalian cells in 1977 has added a new component to the phenomenon of genomic fluidity, which has implications for various subdisciplines of biology.
Uvomorulin‐catenin complex: Cytoplasmic anchorage of a Ca2+‐dependent cell adhesion molecule
Authors: Kemler Rolf , Ozawa Masayuki
Published: February 2005

The cytoplasmic domain of the cell adhesion molecule uvomorulin associates with three independent proteins, named catenins, which are structurally related in different cell types of various species. This complex formation connects uvnomorulin and cytoskeletal structures and might, moreover, be involved in other adhesion‐dependent mechanisms.
Genetics of increased lifespan in drosophila
Authors: Rose Michael R.
Published: February 2005

Natural selection in the laboratory has been used to produce populations of Drosophila with genetically increased lifespan. These populations have been used to determine the physiological basis of postponed ageing and its pleiotropic concomitants. It appears that many loci and a number of physiological alterations are involved in increased lifespan.
Epithelial shape change in mouse embryonic submandibular gland: Modulation by extracellular matrix components
Authors: Nakanishi Yasuo , Ishii Takahiro
Published: February 2005

Early morphogenesis of mouse submandibular gland provides an excellent model for the formation of epithelial lobules as a consequence of epithelial‐mesenchymal interactions. Both proteoglycans and a glycosaminoglycan, high molecular weight components which contain amino‐sugars and hexuronic acids, seem to be important in maintaining the lobular structure through the formation of epithelial basal lamina. Collagen also appears to play a crucial role in this morphogenesis. By visualizing the distribution of collagen fibrils and by changing the concentration of collagen in the gland, we have developed a new hypothesis which emphasizes the mechanical role of mesenchyme in epithelial cleft formation. Precise mechanisms for the involvement of these molecules have not been elucidated, yet it is now clear that knowledge of the function of the extracellular matrix components is a prerequisite for understanding the epithelial‐mesenchymal interactions.
Mating type and mating strategies in Neurospora
Authors: Metzenberg Robert L. , Glass N. Louise
Published: February 2005

In 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

The 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

It 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

Oncogenic 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

Evidence 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

In 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

It 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

Phospholipase 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

In 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

Cell 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

Fundamental 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

This 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

Hydractinia 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

Insect 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

To 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 molecular basis for tropomyosin isoform diversity
Authors: Lees‐Miller James P. , Helfman David M.
Published: February 2005

The tropomyosins are a family of actin filament binding proteins. In multicellular animals, they exhibit extensive cell type specific isoform diversity. In this essay we discuss the genetic mechanisms by which this diversity is generated and its possible significance to cellular function.
The helix‐loop‐helix domain: A common motif for bristles, muscles and sex
Authors: Garrell Joan , Campuzano Sonsoles
Published: February 2005

Three 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

Mouse 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

Free 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

Mitotic 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

Mammalian 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

The 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

Studies 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.
The ageing pineal gland and its physiological consequences
Authors: Reiter Russel J.
Published: February 2005

Melatonin, the chief hormone of the pineal gland, is produced and secreted into the blood in a circadian manner with maximal production always occurring during the dark phase of the light dark cycle. Whereas the 24h rhythm of melatonin production is very robust in young animals including humans, the cycle deteriorates during ageing. The rhythm of melatonin can be substantially preserved during ageing by restricting the food intake of experimental animals; this same treatment increases the life span of the animals. The exogenous administration of melatonin to non‐food restricted animals also reportedly increases their survival. Moreover, melatonin has been shown to have immunoenhancing effects and oncostatic properties. The implication of these studies is that melatonin may have both direct and indirect beneficial effects in delaying ageing processes or it may retard the development of processes (e.g., immunodeficiency and tumor growth) which contribute to a reduced life span.
Why do cancer cells metastasize into particular organs?
Authors: Rusciano Dario , Burger Max M.
Published: February 2005

Metastatic spread of tumor cells is one of the most common causes of death in cancer patients. Therefore, elucidation of the molecular mechanisms that underlie the formation of metastatic colonies has been one of the major objectives of cancer research during the last two decades. In this review we will mainly discuss the mechanisms that cause a malignant cell to grow at a given site rather than at other possible sites, taking into account experimental and clinical evidence published on the subject. As a whole this evidence tends to confirm the hypothesis that organ‐specific colonization by malignant cells often follows very specific and close interactions between the cancer cell and the target organ, either in terms of specific cellular adhesion or growth promotion. In this paper we would like to underscore the fact that cellular adhesion, either specific or unspecific, is a necessary but, by itself, insufficient condition for the development of metastases. It is the ability of the tumor cells to grow at the site where they arrested that ultimately determines whether a metastatic colony develops or fails to develop at that site.
Direct‐developing sea urchins and the evolutionary reorganization of early development
Authors: Raff Rudolf A.
Published: February 2005

The evolution of development can be made accessible to study by exploiting closely related species that exhibit distinct ontogenies. The direct‐developing sea urchin Heliocidaris erythrogramma is closely related to indirect‐developing sea urchins that develop via a feeding larval stage. Superficial consideration would suggest that simple heterochronies resulting in loss of larval features and acceleration of adult features could explain the substitution of direct for indirect development. However, our experiments show that early development has in fact been extensively remodeled, with modified localization of maternal determinants coupled with dissociation of cell cleavage from axis formation resulting in novel patterns of cell lineage differentiation and fate map. Gene expression has undergone concomitant changes.
Problems and paradigms: Genetic sex determination mechanism and evolution
Authors: Hodgkin Jonathan
Published: February 2005

Different animal groups exhibit a surprisingly diversity of sex determination systems. Moreover, even systems that are superficially similar may utilize different underlying mechanisms. This diversity is illustrated by a comparison of sex determination in three well‐studied model organisms: the fruitfly Drosophila melanogaster, the nematode Caenorhabditis elegans, and the mouse. All three animals exhibit male heterogamety, extensive sexual dimorphism and sex chromosome dosage compensation, yet the molecular and cellular processes involved are now known to be quite unrelated. The similarities must have arisen by convergent evolution. Studies of sex determination demonstrate that evolution can produce a variety of solutions to the same basic problems in development.
Structure and evolution of insulins: Implications for receptor binding
Authors: Murray‐Rust J. , McLeod A. N. , Blundell T. L. , Wood S. P.
Published: February 2005

Insulin is a member of a family of hormones, growth factors and neuropeptides which are found in both vertebrates and invertebrates. A common ‘insulin fold’ is probably adopted by all family members. Although the specificities of receptor binding are different, there is possibility of co‐evolution of polypeptides and their receptors.
Mouse models of human single gene disorders I: Non‐transgenic mice
Authors: Darling Susan M. , Abbott Catherine M.
Published: February 2005

Mouse models of human genetic disorders provide a valuable resource for investigating the pathogenesis of genetic disease and for testing potential therapies. The high degree of resolution of linkage mapping in the mouse allows mutant phenotypes to be mapped precisely which, combined with the accurate definition of areas of homology between the mouse and human genomes, greatly facilitates the identification of mouse models. We describe here mouse models of human single gene disorders dividing them into three categories depending on the information available; phenotypic similarities, comparative mapping and identification of the underlying genetic lesion.
The vertebrate limb: A model system to study the Hox/hom gene network during development and evolution
Authors: Duboule Denis
Published: February 2005

The potential of the vertebrate limb as a model system to study developmental mechanisms is particularly well illustrated by the analysis of the Hox gene network. These genes are probably involved in the establishment of patterns encoding positional information. Their functional organisation during both limb and trunk development are very similar and seem to involve the progressive activation in time, along the chromosome, of a battery of genes whose products could differentially instruct those cells where they are expressed. This process may be common to all organisms that develop according to an anterior‐posterior morphogenetic progression. The possible linkage of this system to a particular mechanism of segmentation as well as its phylogenetic implications are discussed.
Problems and paradigms: A mammalian molecular clock?
Authors: Easteal Simon
Published: February 2005

The molecular clock hypothesis remains controversial more than a quarter of a century after it was first proposed. A variety of approaches have been applied to testing the molecular clock in mammals. In many of these studies apparent refutation of the molecular clock has based on false assumptions about the pattern of mammalian evolution. With a few exceptions there now appears to be little evidence for variation in the rate of molecular evolution among mammalian lineages, although comparison of more genes and proteins among a greater variety of mammalian orders is needed before a definitive conclusion can be reached on the issue.
Streamer F mutants and chemotaxis of Dictyostelium
Authors: Newell Peter C. , Liu Gang
Published: February 2005

Streamer F mutants have been found to be useful tools for studying the pathway of signal transduction leading to chemotactic cell movement. The primary defect in these mutants is in the structural gene for the cyclic GMP specific phosphodiesterase. This defect allows a larger and prolonged peak of cyclic GMP to be formed in response to the chemotactic stimulus, cyclic AMP. This characteristic aberrant pattern of cyclic GMP accumulation in the streamer F mutants has been correlated with similar patterns of changes in the influx of calcium from the medium, myosin II association with the cytoskeleton, myosin phosphorylation and a decrease in speed of movement of the amoebae. From these studies a sequence of events can be deduced that leads from cell surface cyclic AMP stimulation to cell polarization prior to movement of the amoebae in response to the chemotactic stimulus.
E.coli hemolysin interactions with prokaryotic and eukaryotic cell membranes
Authors: Hughes Colin , Stanley Peter , Koronakis Vassilis
Published: February 2005

The hemolysin toxin (HlyA) is secreted across both the cytoplasmic and outer membranes of pathogenic Escherichia coli and forms membrane pores in cells of the host immune system, causing cell dysfunction and death. The processes underlying the interaction of HlyA with the bacterial and mammalian cell membranes are remarkable. Secretion of HlyA occurs without a periplasmic intermediate and is directed by an uncleaved C‐terminal targetting signal and the HlyB and HlyD translocator proteins, the former being a member of a transporter superfamily central to import and export of a wide range of substrates by prokaryotic and eukaryotic cells. The separate process by which HlyA is targetted to mammalian cell membranes is dependent upon fatty acylation of a non‐toxic precursor, proHlyA. This is achieved by a novel mechanism directed by the activator protein HlyC, which binds to an internal proHlyA recognition sequence and provides specificity for the transfer of fatty acid from cellular acyl carrier protein.
The mechanism of receptor‐mediated endocytosis: More questions than answers
Authors: Schmid Sandra L.
Published: February 2005

Receptor‐mediated endocytosis occurs via clathrin‐coated pits and is therefore coupled to the dynamic cycle of assembly and disassembly of the coat constituents. These coat proteins comprise part, but certainly not all, of the machinery involved in the recognition of membrane receptors and their selective packaging into transport vesicles for internalization. Despite considerable knowledge about the biochemistry of coated vesicles and purified coat proteins, little is known about the mechanisms of coated pit assembly, receptor‐sorting and coated vesicle formation. Cell‐free assays which faithfully reconstitute these events provide powerful new tools with which to elucidate the overall mechanism of receptor‐mediated endocytosis.
My favorite molecule. The sex‐peptide
Authors: Kubli Eric
Published: February 2005

Injection of a peptide of 36 amino acids into virgin Drosophila females changes their reproductive properties drastically: males are rejected and egg laying is increased. The neuronal and physiological properties of the virgin state are replaced by a new pattern of behavior and stimulation of egg production and deposition. Under natural conditions, the peptide is synthesized by the male and transferred into the female during copulation. The sex‐peptide, therefore, can be considered as a pheromone. In this review, I shall limit my discussion to Drosophila melanogaster.
Exploitation of host signal transduction pathways and cytoskeletal functions by invasive bacteria
Authors: Rosenshie I. , Finlay B. Brett
Published: February 2005

Many bacteria that cause disease have the capacity to enter into and live within eukaryotic cells such as epithelial cells and macrophages. The mechanisms used by these organisms to achieve and maintain this intracellular lifestyle vary considerably, but most mechanisms involve subversion and exploitation of host cell functions. Entry into non‐phagocytic cells involves triggering host signal transduction mechanisms to induce rearrangement of the host cytoskeleton, thereby facilitating bacterial uptake. Once inside the host cell, intracellular pathogens either remain within membrane bound inclusions or escape to the cytoplasm. Those living in the cytoplasm can further pirate the host actin system, using actin as a mechanism to facilitate movement within and between host cells. Organisms remaining within the vacuole have specialized mechanisms for intracellular survival and growth which involve additional communication with the host cell. Some of the processes involved in the various steps of facultative intracellular parasitism are discussed in the context of subverting the host cell cytoskeleton and signal transduction pathways for bacterial benefit.
The assembly of signalling complexes by receptor tyrosine kinases
Authors: Panayotou George , Waterfield Michael D.
Published: February 2005

Cell proliferation in response to growth factors is mediated by specific high affinity receptors. Ligand‐binding by receptors of the protein tyrosine kinase family results in the stimulation of several intracellular signal transduction pathways. Key signalling enzymes are recruited to the plasma membrane through the formation of stable complexes with activated receptors. These interactions are mediated by the conserved, non‐catalytic SH2 domains present in the signalling molecules, which bind with high affinity and specificity to tyrosine‐phosphorylated sequences on the receptors. The assembly of enzyme complexes is emerging as a major mechanism of signal transduction and may regulate the pleiotropic effects of growth factors.