摘要:

AbstractBeckwith‐Wiedemann syndrome is a human congenital disorder characterized by a wide variety of growth abnormalities, including developmental defects and predisposition to certain tumors. Genetic evidence has suggested a role for p57KIP2, a member of a family of cell cycle inhibitory genes, in Beckwith‐Wiedemann syndrome. Two independent groups(1,2)have reported the generation and characterization of mice lacking functional p57KIP2, These mice demonstrate a number of abnormal phenotypes which overlap with, although do not completely recapitulate, Beckwith‐Wiedemann syndrome. These findings advance the molecular characterization of a human disorder, and provide insight into the interplay between regulation of cell division and develo

ISSN:0265-9247    

DOI:10.1002/bies.950191002

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

年代:1997

数据来源: WILEY

摘要:

AbstractThe soil bacteria rhizobia have the capacity to establish nitrogen‐fixing symbiosis with their leguminous host plants. In mostRhizobiumspecies the genes for nodule development and nitrogen fixation have been localized on large indigenous plasmids that are transmissible, allowing lateral transfer of symbiotic functions. A recent paper reports on the complete sequencing of the symbiotic plasmid pNGR234a fromRhizobiumspecies NGR234(1), revealing not only putative new symbiotic genes but also possible mechanisms for evolution and lateral dispersal of symbiotic nitrogen‐fixing abilities among rhizo

ISSN:0265-9247    

DOI:10.1002/bies.950191003

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

年代:1997

数据来源: WILEY

摘要:

AbstractElectrical signaling by neurons depends on the precisely ordered distribution of a wide variety of ion channels on the neuronal surface. The mechanisms underlying the targeting of particular classes of ion channels to specific subcellular sites are poorly understood. Recent studies have identified a new class of protein‐protein interaction mediated by PDZ domains, protein binding modules that recognize specific sequences at the C terminus of membrane proteins. The PDZ domains of a family of synaptic cytoskeleton‐associated proteins, typified by PSD‐95, bind to the intracellular C‐terminal tails of NMDA receptors and Shaker‐type K+channels. This interaction appears to be important in the clustering and localization of these ion channels at synaptic sites. Recognition of specific C‐terminal peptide sequences by different PDZ domain‐containing proteins may be a general mechanism for differential targeting of proteins to a variety of subcellu

ISSN:0265-9247    

DOI:10.1002/bies.950191004

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

年代:1997

数据来源: WILEY

摘要:

AbstractIn vertebrates the antero‐posterior organization of the embryonic body axis is thought to result from the activity of two separate centers, the head organizer and the trunk organizer, as operationally defined by Spemann in the 1920s. Current molecular studies have supported the existence of a trunk organizer activity while the presence of a distinct head inducing center has remained elusive. Mainly based on analyses of headless mutants in mice, it has been proposed that the anterior axial mesoderm plays a determining role in head induction. Recent gain‐ and loss‐of‐function studies in various organisms, however, provide compelling evidence that a largely ignored region, the anterior primitive endoderm, specifies rostral identity. In this review we discuss the emerging concept that the anterior primitive endoderm, rather than the prechordal plate mesoderm, induces head development in the vertebrate

ISSN:0265-9247    

DOI:10.1002/bies.950191005

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

年代:1997

数据来源: WILEY

摘要:

AbstractNeutrophil transepithelial migration is a central component of many inflammatory diseases of the gastrointestinal, respiratory and urinary tracts, and correlates with disease symptoms.In vitromodeling with polarized intestinal epithelial monolayers has shown that neutrophil transepithelial migration can influence crucial epithelial functions, ranging from barrier maintenance to electrolyte secretion. Studies have also demonstrated a dynamic involvement of the epithelium in modulating neutrophil transepithelial migration. Characterization of the molecular interactions between neutrophils and epithelial cells has revealed that transepithelial migration is dependent on the neutrophil β2integrin CD11b/CD18, and does not appear to involve adhesive interactions with the selectins or intercellular adhesion molecule‐1. Recent studies have implicated another transmembrane glycoprotein, CD47, as a crucial component of the transepithelial migration response. While the precise function of CD47 is not known, current evidence suggests that CD47‐dependent events occur after CD11b/CD18‐mediated neutrophil adhesion to the epithelium. This review will highlight key features of the current understanding of the molecular events important in neutrophil migration across epithelial su

ISSN:0265-9247    

DOI:10.1002/bies.950191006

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

年代:1997

数据来源: WILEY

摘要:

AbstractThe oocyte is not only the rarest and the largest cell in the body, but it also has one of the most remarkable life histories. Formed in the fetal ovary and suspended at diplotene of meiosis, it may wait for years before beginning to grow, and not until this process is complete can it resume meiosis and undergo fertilisation. Major changes in the number, morphology and distribution of cytoplasmic organelles occur during growth, and a molecular program for embryogenesis is formed. Specific yolk proteins are absent and much of the RNA and some of the protein are degraded by the cleavage stage. The zona pellucida has been intensively studied, but knowledge of oocyte‐specific genes is otherwise surprisingly patchy given the significance of this cell type and the expansion of reproductive technology. Finally, it is now clear that oocytes are not mere passengers which depend on granulosa cells for nutrition and regulation but actively promote the growth and differentiation of their follicle

ISSN:0265-9247    

DOI:10.1002/bies.950191007

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

年代:1997

数据来源: WILEY

摘要:

AbstractCadherin‐mediated cell‐cell adhesion is perturbed in protein tyrosine kinase (PTK)‐transformed cells. While cadherins themselves appear to be poor PTK substrates, their cytoplasmic binding partners, the Arm catenins, are excellent PTK substrates and therefore good candidates for mediating PTK‐induced changes in cadherin behavior. These proteins, p120ctn, β‐catenin and plakoglobin, bind to the cytoplasmic region of classical cadherins and function to modulate adhesion and/or bridge cadherins to the actin cytoskeleton. In addition, as demonstrated recently for β‐catenin, these proteins also have crucial signaling roles that may or may not be related to their effects on cell‐cell adhesion. Tyrosine phosphorylation of cadherin complexes is well documented and widely believed to modulate cell adhesiveness. The data to date, however, is largely correlative and the mechanism of action remains unresolved. In this review, we discuss the current literature and suggest models whereby tyrosine phosphorylation of Arm catenins contribute to regulation or perturbation of ca

ISSN:0265-9247    

DOI:10.1002/bies.950191008

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

年代:1997

数据来源: WILEY

摘要:

AbstractDNA joining enzymes play an essential role in the maintenance of genomic integrity and stability. Three mammalian genes encoding DNA ligases,LIG1, LIG3andLIG4, have been identified. Since DNA ligase II appears to be derived from DNA ligase III by a proteolytic mechanism, the threeLIGgenes can account for the four biochemically distinct DNA ligase activities, DNA ligases I, II, III and IV, that have been purified from mammalian cell extracts. It is probable that the specific cellular roles of these enzymes are determined by the proteins with which they interact. The specific involvement of DNA ligase I in DNA replication is mediated by the non‐catalytic amino‐terminal domain of this enzyme. Furthermore, DNA ligase I participates in DNA base excision repair as a component of a multiprotein complex. Two forms of DNA ligase III are produced by an alternative splicing mechanism. The ubiqitously expressed DNA ligase III‐α forms a complex with the DNA single‐strand break repair protein XRCC1. In contrast, DNA ligase III‐β, which does not interact with XRCC1, is only expressed in male meiotic germ cells, suggesting a role for this isoform in meiotic recombination. At present, there is very little information about the cellular functions of DN

ISSN:0265-9247    

DOI:10.1002/bies.950191009

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

年代:1997

数据来源: WILEY

摘要:

AbstractRecent findings indicate that substantial cross‐talk may exist between transcriptional and post‐transcriptional processes. Firstly, there are suggestions that specific promoters influence the post‐transcriptional fate of transcripts, pointing to communication between protein complexes assembled on DNA and nascent pre‐mRNA. Secondly, an increasing number of proteins appear to be multifunctional, participating in transcriptional and post‐transcriptional events. The classic example is TFIIIA, required for both the transcription of 5S rRNA genes and the packaging of 5S rRNA. TFIIIA is now joined by the Y‐box proteins, which bind DNA (transcription activation and repression) and RNA (mRNA packaging). Furthermore, the tumour suppressor WT1, at first thought to be a typical transcription factor, may also be involved in splicing; conversely, hnRNP K, abona fidepre‐mRNA‐binding protein, appears to be a transcription factor. Other examples of multifunctional proteins are mentioned: notably PTB, Sxl, La and PU.1. It is now reasonable to assert that some proteins, which were first identified as transcription factors, could just as easily have been identified as splicing factors, hnRNP, mRNP proteins andvice versa. It is no longer appropriate to view gene expression as a series of compartmentalised processes; instead, multifunctional proteins are likely to co‐ordinate different steps o

ISSN:0265-9247    

DOI:10.1002/bies.950191010

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

年代:1997

数据来源: WILEY

摘要:

AbstractAtaxia‐telangiectasia (A‐T) is a pleiotropic recessive disorder characterized cerebellar ataxia, immunodeficiency, specific developmental defects, profound predisposition to cancer and acute radiosensitivity. Functional inactivation of single gene product, ATM, accounts for this compound phenotype. We suggest that ATM acts as a sensor of reactive oxygen species and/or oxidative damage cellular macromolecules, including DNA. In turn, ATM induces signalling through multiple pathways, thereby coordinating acute phase stress responses with cell cycle checkpoint control and repair of oxidative damage. Absence of ATM is proposed to limit the repair of insidious oxidative damage that can occur under normal physiological conditions, ultimately leading to apoptosis of particularly sensitive cells, such as neurons and thymocy

ISSN:0265-9247    

DOI:10.1002/bies.950191011

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

年代:1997

数据来源: WILEY