ISSN:0265-9247    

DOI:10.1002/bies.950180202

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

年代:1996

数据来源: WILEY

摘要:

AbstractEach of the homeotic genes of the bithorax complex of Drosophila defines the identities of more than one body segment. The mechanisms by which this occurs have been elusive. In a recent report, Castelli‐Gair and Akam(1)analyze in detail the control of parasegment 5 and parasegment 6 identities by the bithorax complex geneUbx. Their results indicate that differences in the spatial and temporal expression patterns ofUbxare critical in determining differences between these parasegments. However, dose effects observed by others indicate that parasegment‐specific differences in the level ofUbxexpression are also important. For the other BX‐C genes, parasegment‐specific expression of protein isoforms, or combinatorial control dependent on the expression patterns of other spatially restricted regulators, may also play

ISSN:0265-9247    

DOI:10.1002/bies.950180203

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

年代:1996

数据来源: WILEY

摘要:

AbstractLigand binding to cellular receptors initiates a series of signal transducing cascades that are essential to cellular responses. The Ras pathway is activated in response to a variety of ligands and has been extensively studied. More recently, a novel family of transcription factors (Stats) has been found to be activated in response to many ligands. Three recent publications(1–3)have presented evidence to suggest that these two pathways converge at the level of modulation of Stat function by phosphorylation by MAP kinases. However, each proposes radically different models that are not easily reconciled but invite further experimentatio

ISSN:0265-9247    

DOI:10.1002/bies.950180204

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

年代:1996

数据来源: WILEY

摘要:

AbstractAsymmetric cell division generates two cells that contain different regulatory proteins and express different fates. In an example of asymmetric cell division fromB. subtilis, a site on the membrane of the dividing cell is chosen to establish the initial asymmetry. Recent results(1,2)show that a key regulatory protein, SpollE, is localized to one side of a sporulatingB. subtiliscell, and subsequently functions in an asymmetric manner. SpollE is a phosphatase at the beginning of a regulatory cascade that leads to activation of a cell fate‐determining transcription factor in only one daughter cel

ISSN:0265-9247    

DOI:10.1002/bies.950180205

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

年代:1996

数据来源: WILEY

摘要:

AbstractRan is one of the most abundant and best conserved of the small GTP binding and hydrolyzing proteins of eukaryotes. It is located predominantly in cell nuclei. Ran is a member of the Ras family of GTPases, which includes the Ras and Ras‐like proteins that regulate cell growth and division, the Rho and Rac proteins that regulate cytoskeletal organization and the Rab proteins that regulate vesicular sorting. Ran differs most obviously from other members of the Ras family in both its nuclear localization, and its lack of sites required for post‐translational lipid modification. Ran is, however, similar to other Ras family members in requiring a specific guanine nucleotide exchange factor (GEF) and a specific GTPase activating protein (GAP) as stimulators of overall GTPase activity. In this review, the multiple cellular functions of Ran are evaluated with respect to its known biochemistry and molecular interacti

ISSN:0265-9247    

DOI:10.1002/bies.950180206

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

年代:1996

数据来源: WILEY

摘要:

AbstractMost characters that distinguish one individual from another, like height or weight, vary continuously in populations. Continuous variation of these ‘quantitative’ traits is due to the simultaneous segregation of multiple quantitative trait loci (QTLs) as well as environmental influences. A major challenge in human medicine, animal and plant breeding and evolutionary genetics is to identify QTLs and determine their genetic properties. Studies of the classic quantitative traits, abdominal and sternopleural bristle numbers ofDrosophila, have shown that: (1) many loci have small effects on bristle number, but a few have large effects and cause most of the genetic variation; (2) ‘candidate’ loci involved in bristle development often have large quantitative effects on bristle number; and (3) alleles at QTLs affecting bristle number have variable degrees of dominance, interact with each other, and affect other quantitative traits, including fitness. Lessons learned from this model system will be applicable to studies of the genetic basis of quantitative variation in other

ISSN:0265-9247    

DOI:10.1002/bies.950180207

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

年代:1996

数据来源: WILEY

摘要:

AbstractBasement membranes are thin sheets of extracellular proteins situated in close contact with cells at various locations in the body. They have a great influence on tissue compartmentalization and cellular phenotypes from early embryonic development onwards. The major constituents of all basement membranes are collagen IV and laminin, which both exist as multiple isoforms and each form a huge irregular network by self assembly. These networks are connected by nidogen, which also binds to several other components (proteoglycans, fibulins). Basement membranes are connected to cells by several receptors of the integrin family, which bind preferentially to laminins and collagen IV, andviasome lectin‐type interactions. The formation of basement membranes requires cooperation between different cell types since nidogen, for example, is usually synthesized by cells other than those exposed to the basement membranes. Thus many molecular interactions, of variable affinities, determine the final shape of basement membranes and their preferred subanatomical localizatio

ISSN:0265-9247    

DOI:10.1002/bies.950180208

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe process of chromatin diminution inParascarisandAscarisis a developmentally controlled genome rearrangement, which results in quantitative and qualitative differences in DNA content between germ line and somatic cells. Chromatin diminution involves chromosomal breakage, new telomere formation and DNA degradation. The programmed elimination of chromatin in presomatic cells might serve as an alternative way of gene regulation. We put forward a new hypothesis of how an ancient partial genome duplication and chromatin diminution may have served to maintain the genetic balance in somatic cells and simultaneously endowed the germ line cells with a selective advantage.

ISSN:0265-9247    

DOI:10.1002/bies.950180209

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

年代:1996

数据来源: WILEY

摘要:

AbstractUltraviolet radiation activates the expression of a wide variety of genes, by pathways which differ between the short non‐solar ultraviolet C (UVC) wavelengths, which are strongly absorbed by nucleic acids, and the long solar ultraviolet A (UVA, 320–380 nm) wavelengths, which generate active oxygen intermediates. Intermediate solar ultraviolet (UV) wavelengths in the UVB (290–320 nm) range also contain an oxidative component, but more closely resemble UVC in their gene activating properties. Short wavelength UV, in common with other extracellular stimuli including growth factors, activates signal transduction events that involve both stress‐ and mitogen‐activated protein kinase cascades. The extrapolation of the complex modulation of gene expression that ensues to the consequences of natural UV exposure requires careful attention to the details of doses and wavelength employed in the model experiments. Nevertheless, there is evidence that UVB irrradiation of skin can activate the expression of proteins including immunomodulating cytokines, ornithine decarboxylase and, to a limited extent, nuclear oncogene products, as well as lead to stabilisation of p53. Non‐cytotoxic doses of UVA radiation also lead to the strong activation of several genes which would be expected to have functional relev

ISSN:0265-9247    

DOI:10.1002/bies.950180210

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

年代:1996

数据来源: WILEY

摘要:

AbstractA cabbage looper's job, in many respects not unlike our own, is to survive its early developmental period and grow up healthy, metamorphose into an adult moth, and beget the next generation of loopers. Given its numerous predators, exposure to the continuous barrage of toxic physical, chemical and biological agents delivered by humans in an effort to eradicate it, as well as nature's own hazards, such as the ultraviolet component of sunlight and hazardous natural chemicals in plants that serve to deter ingestion by the looper, it is not difficult to view the looper as a highly stressed organism. However, the looper and its lepidopteran ancestors have been quite successful at resisting such hazards since the Mesozoic Era. The purpose of this brief review will be to examine some of the potential mechanisms by which the looper and its relatives have been able to be so successful over these past 200 million years.

ISSN:0265-9247    

DOI:10.1002/bies.950180211

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

年代:1996

数据来源: WILEY