摘要:

AbstractThe generation of panels of mutant mice by homologous recombination has greatly increased the ability to assess the function of particular gene productsin vivo.The ability to control the developmental stage, the tissue and the nature of the mutation would be an important innovation. A recent report(1)demonstrates that the conservative site‐specific recombination of bacteriophage P1, namely Cre‐lox, can be used successfuly in combination with homologous recombination to generate temporal‐and cell‐restricted mutationsin vivo.The technical advance allows a greater flexibility in gene targeting and will have a significant impact on how complex gene functions are studied

ISSN:0265-9247    

DOI:10.1002/bies.950161202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractPremeiotic association of homologous chromosomes in the yeast,Saccharomyces cerevisiaehas been shown, by means of fluorescentin situhybridization (FISH)(1,2). Time course and mutant studies show that the premeiotic associations are disrupted upon entry into meiosis, to be reestablished shortly before synapsis. The data are consistent with a model in which multiple, unstable interactions bring homologues together, prior to stable joining by recombination(3).

ISSN:0265-9247    

DOI:10.1002/bies.950161203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractA recent paper(1)describing the stage‐specific loss of ubiquitin (UBQ) and ubiquitinated proteins (UBQ‐Ps) during pollen development has raised some interesting questions regarding our understanding of the regulation of protein turnover during cellular differentiation and the specialized development of the pollen grain. The authors, Callis and Bedinger(1), describe experiments in which the profiles of free and protein‐conjugated ubiquitin were examined during pollen development. UBQ and UBQ‐Ps were immunologically detected in extracts of microspores and maturing pollen of maize at six developmental stages. Their results remarkably demonstrate that UBQ and UBQ‐Ps decline to barely detectable levels during the final stages of pollen de

ISSN:0265-9247    

DOI:10.1002/bies.950161204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractInsect vision is nothing if not active. The regular head movements, called saccades, enable the flyDrosophilato keep a straight path in flight despite inequalities in the thrust of the wings. Using their own motion, bees in flight measure the ranges of nearby objects. A long history of research shows that bees discriminate visually in ways that depend on their activity or task, so we must distinguish between vision during flying, fixating or hovering and landing.Bees return again and again for a reward of sugar solution and use their eyes to find their way. In an apparatus that makes them discriminate between two simulataneously visible but regularly interchanged targets, seen at a distance of 27 cm, bees are able to distinguish a remarkable number of simple patterns, but they fail in certain critical cases. The results can be explained with the hypothesis that bees have several broadly tuned overlapping filters with large fields that respond to the predominant orientation in a region of the image, and others for radial and circular patterns. Together with colour, these filters are independent of range. Bees prefer to use landmarks where they can, then global pattern at the largest scale, and lastly the detail around the goal. The way that discrimination of one visual feature is independent of other variables can be explained by models analogous to the colour triangle in colour discrimination.

ISSN:0265-9247    

DOI:10.1002/bies.950161205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe bacterial pathogenListeria monocytogenesdisplays the remarkable ability to reorganize the actin cytoskeleton within host cells as a means for promoting cell‐to‐cell transfer of the pathogen, in a manner that evades humoral immunity. In a series of events commencing with the biosynthesis of the bacterial surface protein ActA, host cell actin and many actin‐associated protein self‐assemble to from rocket‐tail structures that continually grow at sites proximal to the bacterium and depolymerize distally. Widespread interest in the underlying molecular mechanism ofListerialocomotion stems from the likelihood that the dynamic remodeling of the host cell actin cytoskeleton at the cell's leading edge involves mechanistically analogous interactions. Recent advances in our understanding of these fundamental cytoskeletal rearrangements have been achieved through a clearer recognition of the central role of oligo‐proline sequence repeats present in ActA, and these findings provide a basis for inferring the role of analogous host cell proteins in the force‐producing and position‐securing steps in pseudopod and lamellipod formation at the peri

ISSN:0265-9247    

DOI:10.1002/bies.950161206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractLong DNA palindromes pose a threat to genome stability. This instability is primarily mediated by slippage on the lagging strand of the replication fork between short directly repeated sequences close to the ends of the palindrome. The role of the palindrome is likely to be the juxtaposition of the directly repeated sequences by intrastrand base‐pairing. This intra‐strand base‐pairing, if present on both strands, results in a cruciform structure. In bacteria, cruciform structures have proved difficult to detectin vivo, suggesting that if they form, they are either not replicated or are destroyed. SbcCD, a recently discovered exonuclease ofEscherichia coli, is responsible for preventing the replication of long palindromes. These observations lead to the proposal that cells may have evolved a post‐replicative mechanism for the elimination and/or repair of large DNA secondary str

ISSN:0265-9247    

DOI:10.1002/bies.950161207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractEndothelial cells line the inside of all blood vessels, forming a structurally and functionally heterogenous population of cells. Their complexity and diversity has long been recognized, yet very little is known about the molecules and regulatory mechanisms that mediate the heterogeneity of different endothelial cell populations. The constitutive organ‐ and microenvironment‐specific phenotype of endothelial cells controls internal body compartmentation, regulating the trafficking of circulating cells to distinct vascular beds. In contrast, surface molecules associated with the activated cytokine‐inducible endothelial phenotype play a critical role in pathological conditions including inflammation, tumor angiogenesis, and wound healing. Differentiation of the endothelial cell phenotypes appears to follow similar mechanisms to the differentiation of hematopoietic cells, with the exception that endothelial cells maintain transdifferentiating competence. The present review offers a scheme of endothelial cell differentially expressed endothelial cell molecules as targets for directed therapeutic interve

ISSN:0265-9247    

DOI:10.1002/bies.950161208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThis article focuses on the occasional individuals of many species that live longer than is usual for their populations – here called longevity outliers. They appear to be exceptions to the usual patterns of mortality rates that increase with age. There is no model of survivorship that accommodates all of these individuals. They are less vulnerable to the usual causes of death than most in their populations. There are hints of genetically based mechanisms in the form of life‐prolonging genes in invertebrates and genetic resistance to fatal diseases in higher organisms. The reasons why longevity outliers ultimately die are not known. Based on well‐established trends, I predict that there will be many more humans reaching very old ages in the next ce

ISSN:0265-9247    

DOI:10.1002/bies.950161209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractOsteopotin is a secreted glycosylated phosphoprotein found in bone and other normal and malignant tissues. Osteopontin can be autophosphorylated on tyrosine residues and can also be phosphorylated on serine and threonine residues by several protein kinases. Autophosphorylation of osteopontin may generate sites for specific interactions with other proteins on the cell surface and/or within the extracelluar matrix. These interactions of osteopontin are thought to be essential for bone mineralization and function. The polyaspartic acid motif of osteopontin, in combination with neighboring sequences that include serine residues phosphorylated by protein kinases, could fold and assemble into a molecular structure that participates in the mineralization of the bone matrix.

ISSN:0265-9247    

DOI:10.1002/bies.950161210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractSuperoxide is produced by a NADPH oxidase of phagocytic cells and contributes to their microbicidal activities. The oxidase is activated when receptors in the neutrophil plasma membrane bind to the target microbe. These receptors recognise antibodies and complement fragments which coat the target cell. The oxidase electron transport chain, located in the plasma membrane, comprises a low potential cytochromebheterodimer (gp 91‐phoxand p22‐phox) associated with FAD. It is non‐functional until at least three proteins, p67‐phox, p47‐phoxand p21rac(and possibly others), move from the cytosol to dock on the cytochromeb.The docking involves the interaction of SH3domains may become exposed follwoing phosphorylation of p47‐phoxby protein kinase C or, in model systems, by addition of arachidonic acid to reconstitution mixtures. Following the docking process the electron‐transporting component is able to transfer electrons from NADPH to oxygen. This electrogenic event is charge‐compensated by the opening of a prton channel. Components of the oxidase are expressed in non‐phagocytes, where their function is uncretain but could be related to some signal funct

ISSN:0265-9247    

DOI:10.1002/bies.950161211

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY