摘要:

AbstractSporulation in the moldNeurospora crussacan proceed along three very different pathways, leading to the production of three types of spores. Two asexual sporulation pathways that lead to the formation of macroconidia and microconidia involve budding from hyphae by two different mechanisms. A much more complex sexual reproductive pathway involves the formation of a fruiting body called a perithecium, in which meiosis takes place and ascospores are formed in sac‐like cells called asci. Numerous mutations exist that affect these developmental pathways, and genes have been isolated that are expressed preferentially during sporulation. TheNeurosporasporulation pathways offer a simple system with which to study mechanisms and regulation of development that are usually obscured by complex cell‐cell interactions involved in animal and plant developm

ISSN:0265-9247    

DOI:10.1002/bies.950150602

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

年代:1993

数据来源: WILEY

摘要:

AbstractBinding of a growth factor (GF) to its specific receptor on the cell surface causes the initiation of a signal transduction cascade which eventually results in mitosis. GF:receptor complexes are removed from the cell surface via receptor‐mediated endocytosis, a process which involves clathrin‐coated pits. After internalization into the endosomal compartment, a significant pool of GFs and GF receptors escape recycling to the cell surface and are sorted to the degradation pathway. The ligandinduced internalization and lysosomal degradation of GF receptors result in the dramatic loss of surface receptors, a phenomenon termed receptor down‐regulation. In this review, we discuss relevant biochemical, morphological and kinetic studies of the mechanism of GF endocytosis, and the possible role of this process in mitogenic signaling by growth factor rece

ISSN:0265-9247    

DOI:10.1002/bies.950150603

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

年代:1993

数据来源: WILEY

摘要:

AbstractTheDrosophilaposition‐specific (PS) integrins are members of the integrin family of cell surface receptors and are thought to be receptors for extracellular matrix components. Each PS integrin consists of an α subunit, αPS1or αPS2, and a βPSsubunit. Mutations in the βPSsubunit and the αPS2subunit have been characterised and reveal that the PS integrins have an essential role in the adhesion of different cell layers to each other. The PS integrins are especially required for the function of the cell‐matrix‐cell junctions, where the muscles attach to the epidermis and where one surface of the developing wing adheres to the other. These junctions are similar to vertebrate focal adhesions and hemidesmosomes, which also contain integrins. Integrin‐mediated cell to cell adhesion via the extracellular matrix provides a way for tissues to adhere to each other without intermingling o

ISSN:0265-9247    

DOI:10.1002/bies.950150604

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe recognition of extracellular molecules by cell surface receptors is the principal mechanism used by cells to sense their environment. Consequently, signals transduced as a result of these interactions make a major contribution to the regulation of cellular phenotype. Historically, particular emphasis has been placed on elucidating the intracellular consequences of growth factor and cytokine binding to cells. In addition to these interactions, however, cells are usually in intimate contact with a further source of complex structural and functional information, namely immobilised extracellular matrix and/or cell surface adhesion proteins. A key question in recent years has been whether cells use the myriad of adhesion protein‐receptor interactions purely for structural and migratory function, or whether these interactions also make a more varied contribution to cell phenotype. Here we review dynamic aspects of the function of one major class of adhesion receptor, the integrins. In particular, we focus on the evidence for shape changes in integrin molecules, the mechanisms responsible for regulating ligand binding, and the signals transduced following integrin occupanc

ISSN:0265-9247    

DOI:10.1002/bies.950150605

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

年代:1993

数据来源: WILEY

摘要:

AbstractA framework for understanding the complex movements of mitosis and meiosis has been provided by the recent discovery of microtubule motor proteins, required for the proper distribution of chromosomes or the structural integrity of the mitotic or meiotic spindle. Although overall features of mitosis and meiosis are often assumed to be similar in mechanism, it is now clear that they differ in several important aspects. These include spindle structure and assembly, and timing of chromosome segregation to opposite poles. Here we review progress in the functional characterization of several newly identified microtubule motor proteins, emphasizing their possible roles in spindle structure and function.

ISSN:0265-9247    

DOI:10.1002/bies.950150606

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

年代:1993

数据来源: WILEY

摘要:

AbstractTumour‐associated genetic changes frequently involve DNA translocation or deletion. Many of these events will have arisen from initial genomic damage, induced by either the activity of endogenous metabolic processes or from exposure to environmental genotoxic agents. Although initial genomic damage will have been widely distributed, tumorigenic events are confined to certain DNA target sites. Furthermore, within these target sites there appear to be regions of preferential DNA rearrangement, and examination of these sites implies that the location and extent of such rearrangement may be influenced by DNA primary and secondary structure rather than simply by the point of damage. We selectively review evidence relating to DNA structures that may predispose certain regions of the genome to damage‐induced rearrangement, and discuss the possible role of interstitial, inverted telomere‐like sequence arrays in promoting chromosomal events of a type known to be associated with some human and animal tu

ISSN:0265-9247    

DOI:10.1002/bies.950150607

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis review is primarily concerned with two key issues in research on dystrophin: (1) how the protein interacts with the plasma membrane of skeletal muscle fibres and (2) how an absence of dystrophin gives rise to Duchenne muscular dystrophy. In relation to the first point, we suggest that the post‐translational acylation of dystrophin may contribute to its interaction with the plasma membrane. Regarding the second point, it is generally considered that an absence of dystrophin makes the plasma membrane susceptible to damage by contraction/relaxation cycles. In this connection, we propose that the progressive nature of Duchenne dystrophy, and the phenotypic characteristics ofmdxmice, are more consistent with dystrophin functioning as a mechanical transducer that transmits growth stimuli from the enlarging skeleton to the muscle. On the basis of this hypothesis, dystrophin‐deficient muscles would be unable to grow at the same rate as the skele

ISSN:0265-9247    

DOI:10.1002/bies.950150608

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

年代:1993

数据来源: WILEY

摘要:

AbstractWerner syndrome (WS) is an inherited disorder that produces somatic stunting, premature ageing and early onset of degenerative and neoplastic diseases. Cultured fibroblasts derived from subjects with WS are found to undergo premature replicative senescence and thus provide a cellular model system to study the disorder. Recently, several overexpressed gene sequences isolated from a WS fibroblast cDNA library have been shown to possess the capacity to inhibit DNA synthesis and disrupt many normal biochemical processes. Because a similar constellation of genes is overexpressed in WS and senescent normal fibroblasts, these data suggest the existence of a common molecular genetic pathway for replicative senescence in both types of cell. We propose that the primary defect in WS is a mutation in a gene for a trans‐acting repressor protein that reduces its binding affinity for shared regulatory regions of several genes, including those that encode inhibitors of DNA synthesis (IDS). The mutant WS repressor triggers a sequence of premature expression of IDS and other genes, with resulting inhibition of DNA synthesis and early cellular senescence, events which occur much later in normal cell

ISSN:0265-9247    

DOI:10.1002/bies.950150609

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

年代:1993

数据来源: WILEY

摘要:

AbstractAlpha‐fetoprotein (AFP)AFP, alpha‐fetoprotein; T3R, thyroid hormone (triiodothyronine) receptor; RAR, retionic acid receptor; erbA, putative thyroid hormone receptor proto‐oncogene products; VDR, vitamin D receptor; MR, mineralocorticoid receptor; GR, glucocorticoid receptor; PR, progesterone receptor; AR, androgen receptor; HRE, hormone response element on DNA; RXR, retionic‐X‐receptor; RAP, receptor auxiliary (accessory) proteins; E, estrogen.is a tumor‐associated fetal marker, associated both with tumor growth and with birth defects. AFP, whose precise function is unknown, has been classified as belonging to a protein superfamily together with albumin and vitamin D‐binding (Gc) protein. AFP has been shown to bind various ligands in vitro including fatty acids, estrogens, thyroid hormones and retinoic acids. The steroid/thyroid nuclear receptor superfamily of proteins has recently become a major focus of biomedical investigation regarding regulation of gene expression. These receptors are thought to bind to DNA‐hormone response elements (HRE) that affect growth, development, differentiation, reproduction and homeostasis. The HREs are known to share DNA sequences with the various members of the nuclear receptor superfamily. In the present report, the possibility of a leucine‐zipper dimerization (heptad) motif in the carboxy‐terminal third domain of both rodent and human AFP is postulated. The presence of nine such hydrophobic repeats in the third domain of the AFP molecule mimics the heptad dimerization repeats found in the retinoic acid, thyroid, e‐erbA and other members of the nuclear receptor superfamily. Computer analysis revealed that the most conservative matching occurred between AFP and the retinoic acid class of receptors. However, other superfamily members displayed 40–60% homology with 5 of 9 AFP heptads. These findings could provide a possible mechanism for explaining the growth‐regulatory properties (both inhibition and enhancement) that have been ascribed

ISSN:0265-9247    

DOI:10.1002/bies.950150610

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

年代:1993

数据来源: WILEY

ISSN:0265-9247    

DOI:10.1002/bies.950150612

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

年代:1993

数据来源: WILEY