摘要:

AbstractSR proteins are essential for the splicing of messenger RNA precursorsin vitro, where they also alter splice site selection in a concentration‐dependent manner. Although experiments involving overexpression or dominant mutations have confirmed that these proteins can influence RNA processing decisionsin vivo, similar results with loss‐of‐function mutations have been lacking. Now, a system for genetic depletion of the chicken B cell line DT40 has revealed that the SR protein ASF/SF2 (alternative splicing factor/splicing factor 2) is essential for viability in these cells(1). This study opens the way for a complete functional dissection of this protein, and other SR proteins,in

ISSN:0265-9247    

DOI:10.1002/bies.950190302

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

年代:1997

数据来源: WILEY

摘要:

AbstractCell cycle arrest in M phase can be induced by the failure of a single chromosome to attach properly to the mitotic spindle. The same cell cycle checkpoint mediates M phase arrest when cells are treated with drugs that either disrupt or hyperstabilize spindle microtubules. Study of yeast mutants that fail to arrest in the presence of microtubule disruptors identified a set of genes important in this checkpoint pathway. Two recent papers report the cloning of human andXenopushomologues of one of these yeast genes, calledMAD2(for mitotic arrest deficient‐2)(1,2). Introduction of antibodies to the MAD2 protein into living mammalian cells orXenopusegg extracts abrogates the M phase arrest induced by microtubule inhibitors. This and other recent developments suggest a model for the M phase checkpoint in which unattached kinetochores inhibit the ubiquitination of proteins whose proteolysis is necessary for chromatid separation and exit from mitosi

ISSN:0265-9247    

DOI:10.1002/bies.950190303

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

年代:1997

数据来源: WILEY

摘要:

AbstractLithium, despite its simple structure, has numerous biological effects. It also has a remarkable therapeutic effect in the prophylactic treatment of manic depression, and is finding a role in controlling aggressive and self‐mutilating behavior. The special feature of lithium is that it only acts on overactive systems to bring them back to normal, without affecting the stable system. The mechanisms of action of this simple cation are still largely unknown although the inositol depletion theory is the most widely accepted model. A recent paper(1)described a different molecular mechanism for its effect on development, which may also explain its action in manic depressio

ISSN:0265-9247    

DOI:10.1002/bies.950190304

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

年代:1997

数据来源: WILEY

摘要:

AbstractDuring embryogenesis, cell division must be spatially and temporally regulated with respect to other developmental processes. Leech embryos undergo a series of unequal and asynchronous cleavages to produce individually recognizable cells whose lineages, developmental fates and cell cycle properties have been characterized. Thus, leech embryos provide an opportunity to examine the regulation of cell division at the level of individual well‐characterized cells within a community of different types of cells. Isolation of leech homologues of some of the highly conserved regulators of the cell division cycle, and characterization of their patterns of maternal and zygotic expression, indicate that the cell divisions of early leech embryos are regulated by cell type‐specific mechanisms. These studies with leech embryos contribute to the emerging appreciation of the diverse mechanisms by which animals regulate cell division during early developm

ISSN:0265-9247    

DOI:10.1002/bies.950190305

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

年代:1997

数据来源: WILEY

摘要:

AbstractA wide range of biological processes, in all eukaryotes and in some prokaryotes, are controlled by rhythms with a period close to 24 hours. The circadian oscillator, which is responsible for generating these rhythms, is controlled by light signals that maintain its synchrony with the environmental day/night cycle. Higher plants exhibit many circadian rhythms, including rhythms in the transcription of specific genes. Molecular tools derived from such clock‐controlled genes have led to the identification of several circadian rhythm mutants in the genetic model,Arabidopsis thaliana. The extensive understanding of photoperception in this species will make it a powerful system with which to investigate the light regulation of circadian rhythms. We compare Arabidopsis rhythms to the results from other systems, and discuss these data with respect to the current phototransduction model

ISSN:0265-9247    

DOI:10.1002/bies.950190306

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

年代:1997

数据来源: WILEY

摘要:

AbstractAdipose tissue plays an important role in mammalian energy equilibrium not only as a lipid‐dissipating, i.e. energy‐storing, tissue (white adipose tissue), but also as an energy‐dissipating one (brown adipose tissue). Brown adipocytes have the ability of facultative heat production due to a unique mitochondrial protein, the uncoupling protein (UCP). Differentiation of white and (to a lesser extent) brown adipocytes has been studied in different cell culture systems, which has led to the identification of external inducers, second messenger pathways and transcription factors involved in adipocyte differentiation. Functional differentiation of white adipocytes implies adipose conversion, whereas in brown adipocytes it insinuates additionally the development of a thermogenic function. This review discusses recent advances in the elucidation of the pathways responsible for, and the molecular bases of, adipose conversion on the one hand and development of the thermogenic properties of brown adipocytes on the

ISSN:0265-9247    

DOI:10.1002/bies.950190307

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

年代:1997

数据来源: WILEY

摘要:

AbstractTo understand how morphological characters change during evolution, we need insight into the evolution of developmental processes. Comparative developmental approaches that make use of our fundamental understanding of development in certain model organisms have been initiated for different animal systems and flowering plants. Nematodes provide a useful experimental system with which to investigate the genetic and molecular alterations underlying evolutionary changes of cell fate specification in development, by comparing different species to the genetic model systemCaenorhabditis elegans.In this review, I will first discuss the different types of evolutionary alterations seen at the cellular level by focusing mainly on the analysis of vulva development in different species. The observed alterations involve changes in cell lineage, cell migration and cell death, as well as induction and cell competence. I then describe a genetic approach in the nematodePristionchus pacificusthat might identify those genetic and molecular processes that cause evolutionary changes of cell fate specification.

ISSN:0265-9247    

DOI:10.1002/bies.950190308

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

年代:1997

数据来源: WILEY

摘要:

AbstractUnlike the most well‐characterized prokaryotic polymerase,E. ColiDNA pol I, none of the eukaryotic polymerases have their own 5′ to 3′ exonuclease domain for nick translation and Okazaki fragment processing. In eukaryotes, FEN‐1 is an endo‐and exonuclease that carries out this function independently of the polymerase molecules. Only seven nucleases have been cloned from multicellular eukaryotic cells. Among these, FEN‐1 is intriguing because it has complex structural preferences; specifically, it cleaves at branched DNA structures. The cloning of FEN‐1 permitted establishment of the first eukaryotic nuclease family, predicting thatS. cerevisiaeRAD2 (S. pombeRad13) and its mammalian homolog, XPG, would have similar structural specficity. The FEN‐1 nuclease family includes several similar enzymes encoded by bacteriophages. The crystal structures of two enzymes in the FEN‐1 nuclease family have been solved and they provide a structural basis for the interesting steric requirements of FEN‐1 substrates. Because of their unique structural specificities, FEN‐1 and its family members have important roles in DNA replication, repair and, potentially, recombination. Recently, FEN‐1 was found to specifically associate with PCNA, explaining some aspects of FEN‐1 function during DNA replication and

ISSN:0265-9247    

DOI:10.1002/bies.950190309

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

年代:1997

数据来源: WILEY

摘要:

AbstractMammalian sperm undergo discharge of a single, anterior secretory granule following their attachment to the zona pellucida surrounding the oocyte. This secretory discharge is known for historical reasons as the acrosome reaction. It fulfils a number of purposes and without it, sperm are unable to penetrate the zona pellucida and fuse with the oocyte. In this review, we focus on the role of the acrosome reaction in the development of fusion competence in sperm. Any naturally occurring membrane fusion has two major sequential steps: a docking or adhesion step, in which two membranes adhere, and a fusion step, in which their lipid bilayers are destabilized and merged and a cellular compartment is either created or destroyed. Recent evidence suggests that there is an important role for oocyte integrins and sperm‐bound disintegrins in mammalian sperm/oocyte adhesion and fusion. The fusion mechanism employed by sperm remains poorly understood, however, and circumstantial evidence suggests it is more complex than the interaction between a single protein species and its target. Sperm/oocyte fusion is probably the most accessible eukaryotic model for intercellular fusion currently available, partly because it is temporally separated from gene expression. Elucidation of the mechanism of sperm/oocyte fusion may throw light on the mechanism of other intercellular fusions such as myoblast fusion, and the evolutionary relationship of intercellular membrane fusion to intracellular membrane fusio

ISSN:0265-9247    

DOI:10.1002/bies.950190310

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

年代:1997

数据来源: WILEY

摘要:

AbstractKnockout experiments inTetrahymenashow that linker histone H1 is not essential for nuclear assembly or cell viability. These results, together with a series of biochemical and cell biological observations, challenge the existing paradigm that requires linker histones to be a key organizing component of higher‐order chromatin structure. The H1 Knockouts also reveal a much more subtle role for H1. Instead of acting as a general transcriptional repressor, H1 is found to regulate a limited number of specific genes. Surprisingly, H1 can both activate and repress transcription. We discuss how this architectural protein might accomplish this important regulatory rol

ISSN:0265-9247    

DOI:10.1002/bies.950190311

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

年代:1997

数据来源: WILEY