摘要:

AbstractDevelopment of gene transfer systems provides a key tool for understanding gene function. Exciting and often unexpected consequences from embryo manipulations are yielding insights into molecular mechanisms underlying development under normal and pathogenic states, and are providing animal models for diseases. Contributing to this progress is the elegant work on c‐fos(1), where Wagner and coworkers identify this proto‐oncogene as a primary factor which directs cell differentiation along the osteoclast/macrophage lineages, and thus regulates bone remodeling. Their studies support a link between skeletogenesis, marrow formation and hematopoiesis, and may help to delineate mechanisms underlying the oncogenic transformation of skeletal and hematopoietic ce

ISSN:0265-9247    

DOI:10.1002/bies.950170402

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

年代:1995

数据来源: WILEY

摘要:

AbstractAnalysis of the light‐induced changes of cytosolic Ca2+([Ca2+]i) in photoreceptor cells has been taken a step further with two recently published studies(1,2). In one, changes in [Ca2+]iwere measured in single detached rod outer segments from Gecko in response to various light intensities. The advances of the other(2)are embodied in its employment of transgenic Drosophila, whose photoreceptors express a visual pigment that is insensitive to the wavelength of light used in the fluorescence imaging of [Ca2+]i. These studies provide a better basis for understanding the regulation of Ca2+‐mediated events in photoreceptor ce

ISSN:0265-9247    

DOI:10.1002/bies.950170403

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

年代:1995

数据来源: WILEY

摘要:

AbstractEthylene (C2H4) is a gaseous plant hormone produced by higher and lower (green) plants and, when grown on appropriate substrates, also by fungi, yeasts and bacteria. Ethylene is involved in many developmental processes in plants and is biologically active in trace amounts (10 – 100 nl/I of air) that may be present in the outside air due to industrial air pollution(1). Fruit ripening and flower senescence especially, in a variety of commercially important crops, are dramatically stimulated by ethylene. Following characterization of the genes coding for the key enzymes in ethylene biosynthesis, i.e. ACC synthase and ACC oxidase, it has become clear that their expression is regulated in a complex manner involving developmental, hormonal and tissue‐specific factors. This was recently very elegantly demonstrated for the expression of ACC oxidase genes in developing petunia flowers by Tanget al.(2). The spatial and temporal expression patterns, especially in the reproductive organs, suggest a hitherto unknown role for ethylene in reproductive processes such as the self‐incompatible response and the secretion of cellular exudate by the stigma and ne

ISSN:0265-9247    

DOI:10.1002/bies.950170404

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

年代:1995

数据来源: WILEY

摘要:

AbstractExpression and transposition of theSuppressor‐mutator (Spm)transposon of maize are controlled by interacting epigenetic and autoregulatory mechanisms. Methylation of critical element sequences prevents both transcription and transposition, heritably inactivating the element. The promoter, comprising the terminal 0.2 kb of the element, and a 0.35‐kb, highly GC‐rich, downstream sequence are the methylation target sequences. The element encodes two proteins necessary for transposition, TnpA and TnpD. There are multiple TnpA binding sites, both in the 5′ terminal promoter region and at the element's 3′ end. In addition to its role in transposition, TnpA is both a positive and a negative regulator of transcription. TnpA represses the element's promoter when it is not methylated. When the element is inactive and its promoter methylated, TnpA activates the methylated promoter and facilitates both its transient and heritable deme

ISSN:0265-9247    

DOI:10.1002/bies.950170405

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe appendages ofDrosophiladevelop from the imaginal discs. During the extensive growth of these discs cell lineages are for the most part unfixed, suggesting a strong role for cell‐cell interactions in controlling the final pattern of differentiation. However, during early and middle stages of development, discs are subdivided by strict lineage restrictions into a small number of spatially distinct compartments. These compartments appear to be maintained by stably inheriting states of gene expression; the compartmentspecific expression of two such ‘selector’ ‐ like genes,engrailedandapterous, are critical for anterior‐posterior and dorso‐ventral compartmentalization, respectively. Recent work suggests that one purpose of compartmentalization is to establish regions of specialized cells near compartment boundariesviaintercompartmental induction, using molecules like thehedgehogprotein. Thus, compartments can act as organizing centers for patterning within compartments. Evidence for non‐compartmental patterning mechanisms will also

ISSN:0265-9247    

DOI:10.1002/bies.950170406

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

年代:1995

数据来源: WILEY

摘要:

AbstractMammals have an XX:XY system of chromosomal sex determination in which a small heterochromatic Y controls male development. The Y contains the testis determining factorSRY, as well as several genes important in spermatogenesis. Comparative studies show that the Y was once homologous with the X, but has been progressively degraded, and now consists largely of repeated sequences as well as degraded copies of X linked genes. The small original X and Y have been enlarged by cycles of autosomal addition to one partner, recombination onto the other and continuing attrition of the compound Y. This addition–attrition hypothesis predicts that the pseudoautosomal region of the human X is merely the last relic of the latest addition. Genes (includingSRY) on the conserved or added region of the Y evolved functions in male sex determination and differentiation distinct from the general functions of their X‐linked partners. Although the gonadogenesis pathway is highly conserved in vertebrates, its control has probably changed radically and rapidly in vertebrate – even mammalian – ev

ISSN:0265-9247    

DOI:10.1002/bies.950170407

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

年代:1995

数据来源: WILEY

摘要:

AbstractThere is increasing evidence to suggest that cytoplasmic tyrosine kinases of the Src family have a pivotal role in the regulation of a number of cellular processes. Members of this family have been implicated in cellular responses to a variety of extracellular signals, such as those arising from growth factors and cell‐cell interactions, as well as in differentiative and developmental processes in both vertebrates and invertebrates. A better understanding of the regulation and of the structure‐function relationships of these enzymes might aid in the development of specific ways to interfere with their action, as well as serving as a paradigm for regulation of other protein tyrosine kinases that have SH2 and SH3 domains. In this review we will first discuss the regulation of Src family protein tyrosine kinases, with particular emphasis on their SH2 and SH3 domains. We will then briefly review other non‐receptor protein tyrosine kinases that have SH2 and SH3 do

ISSN:0265-9247    

DOI:10.1002/bies.950170408

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

年代:1995

数据来源: WILEY

摘要:

AbstractOne major milestone in the development of the sea urchin embryo is the assembly of a single cilium on each blastomere just before hatching. These cilia are constructed both from pre‐existing protein building blocks, such as tubulin and dynein, and from a number of 9+2 architectural elements that are synthesizedde novoat ciliogenesis. The finite or quantal synthesis of certain key architectural proteins is coincident with ciliary elongation and proportional to ciliary length. Upon deciliation, the synthesis of architectural proteins occurs anew, a new cilium grows, and the stores of various building blocks are replenished. This routine of coordinated ciliary gene expression may be replayed experimentally many times without delaying normal development. The ability to regenerate cilia has allowed elucidation of these various protein synthetic relationships and has led to the discovery of the pathways by which membrane‐associated tubulin and axoneme‐associated architectural proteins are conveyed into the highly compartmentalized growing cilium. The sea urchin embryo thus provides a very convenient model system for studies of ciliary assembly and maintenance, coordinate gene expression and membrane dyn

ISSN:0265-9247    

DOI:10.1002/bies.950170409

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

年代:1995

数据来源: WILEY

摘要:

AbstractOver the last decade, the c‐mybgene and its protein product, Myb, have undergone extensive examination and manipulation in hemopoietic tissues. Although it is rarely disputed that, as a transcription factor, Myb regulates cell cycling, proliferation and differentiation, identification of genes directly controlled by Myb has been surprisingly difficult. More recently, genes with promoter regions that contain Myb recognition sequences have been identified, but a direct proliferative response to Mybviathese ‘target genes’ has yet to be demonstrated. Mutagenesis studies have defined domains of the protein which influence its transcriptional activity and transforming potential; however how the molecule interacts with itself and with other cellular factors is only beginning to be understood. A broader examination of c‐mybexpression in normal and malignant tissues suggests an analogous role for Myb in proliferation, differentiation and transformation of nonhemopoietic

ISSN:0265-9247    

DOI:10.1002/bies.950170410

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe members of the phylumCnidaria(corals, sea anemones, medusae) are all equipped with stinging cells (cnidocytes, nematocytes), which serve mainly in prey capture and defense. The secretory product of these cells is a most complicated extrusome consisting of a cyst containing a tubule and a liquid matrix. Mechanical stimulation of the cell's cnidocil apparatus by a prey or an offender leadsviabioelectrical signal transduction to the explosive discharge of the cnidocyst. In stenoteles ofHydrathis process, during which the tubule is everted out of the cyst, takes less than 3 msec. The forces involved are partly due to spring‐like tensions stored in the collagenous structural compartment, and partly to an osmotically generated intracapsular pressure, which can amount to 150 bar (1.5 × 107Pa). The osmotic machinery depends on the presence in the cyst's matrix of inorganic cations (either K+, Mg2+or Ca2+) and rare polyanions (poly‐γ‐L‐glutamates), which, so far, have not been reported from recently evolved eukaryotes. The discharging cyst acts like a self‐reloading syringe, injecting poison and other components into the target. Since the cnidocytes are incapable of regenerating their exocytosed cysts, they have to be replaced by new cells derived by differentiation from pluripotent stem cells (intersti

ISSN:0265-9247    

DOI:10.1002/bies.950170411

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

年代:1995

数据来源: WILEY