ISSN:0265-9247    

DOI:10.1002/bies.950190802

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

年代:1997

数据来源: WILEY

摘要:

AbstractA key characteristic of an animal's nervous system is that it can respond to brief environmental stimuli with lasting changes in its structure and function. These changes are triggered by specific patterns of neuronal electrical activity and are manifested as changes in the strength and patterns of synaptic connectivity between activated neurons. The biochemical mechanisms that control these changes are unclear, but cytoplasmic rises in Ca2+levels may play a critical role, especially in regulating neuronal gene expression for making activity‐induced synaptic changes permanent. Recently, two reports have explored the spatial features by which activity‐induced rises in Ca2+levels activate transcription factors and gene expression(1,2). The reports suggest that Ca2+influx acts both locally at the synapse and distantly within the nucleus to regulate transcription factors and gene expression. The results also show that regulatory elements within genes can respond differentially, depending on spatial differences in intracellular Ca2+rises. These reports suggest new spatial mechanisms by which Ca2+‐dependent gene expression could contribute to activity‐dependent synaptic

ISSN:0265-9247    

DOI:10.1002/bies.950190803

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

年代:1997

数据来源: WILEY

摘要:

AbstractThe evolutionarily conserved genomic organization of theHoxgenes has been a puzzle ever since it was discovered that their order along the chromosome is similar to the order of their functional domains along the antero‐posterior axis. Why has this colinearity been maintained throughout evolution? A close look at regulatory sequences from the mouseHoxclusters(1,2)suggests that enhancer sharing between adjacentHoxgenes may be one reason. Moreover, characterizing the activity of one of these mouse enhancers inDrosophila(2)illustrates that despite many similarities, not allHoxclusters are built in the same wa

ISSN:0265-9247    

DOI:10.1002/bies.950190804

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

年代:1997

数据来源: WILEY

摘要:

AbstractThe transparent sea urchin embryo provides a laboratory for study of morphogenesis. The calcareous endoskeleton is formed by a syncytium of mesenchyme cells in the blastocoel. The locations of mesenchyme in the blastocoel, the size of the skeleton, and even the branching pattern of the skeletal rods, are governed by interactions with the blastula wall. Now Guss and Ettensohn(1)show that the rate of deposition of CaCO3in the skeleton is locally controlled in the mesenchymal syncytium, as is the pattern of expression of three genes involved in skeleton formation. They propose that short range signals emanating from the blastula wall regulate many aspects of the biomineralization process.

ISSN:0265-9247    

DOI:10.1002/bies.950190805

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

年代:1997

数据来源: WILEY

摘要:

AbstractAt least seven orphan members of the nuclear receptor superfamily are transcriptionally regulated by the steroid hormone ecdysone and expressed during the onset ofDrosophilametamorphosis. A recent paper provides functions for two of these receptors, E75B and DHR3, throughtrans‐regulation and heterodimerization(1). DHR3 appears to function as a switch that defines the transition from a late larva to a prepupa, and E75B functions as a timer that modulates this transition. This study provides a biological function for orphan receptor interactions during developmen

ISSN:0265-9247    

DOI:10.1002/bies.950190806

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

年代:1997

数据来源: WILEY

摘要:

AbstractOur understanding of epithelial development inDrosophilahas been greatly improved in recent years. Two key regulators of epithelial polarity, Crumbs andDE‐cadherin, have been studied at the genetic and molecular levels and a number of additional genes are being analyzed that contribute to the differentiation of epithelial cell structure. Epithelial architecture has a profound influence on morphogenetic movements, patterning and cell‐type determination. The combination of embryological and genetic/molecular tools inDrosophilawill help us to elucidate the complex events that determine epithelial cell structure and how they relate to morphogenesis and other developmental proces

ISSN:0265-9247    

DOI:10.1002/bies.950190807

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

年代:1997

数据来源: WILEY

摘要:

AbstractNew molecular markers for epidermal stem cells have enabled their isolation bothin vitroand from the epidermis lying between hair follicles. Micro‐dissection experiments have localised a second population of stem cells within hair follicles. Epidermal stem cells have a patterned distributionin vivo. The patterning can be reconstitutedin vitro, showing that it is generated by interactions between keratinocytes and that the differentiation of epidermal stem cells is regulated by signals from other keratinocytes. Recent evidence from transgenic mice suggests that stem cell behaviour in the gut may be regulated by similar cell‐cell interactionsin vivo. Candidate genes for mediating these interactions are the homologues ofDrosophilacell fate patterning genes such asNotchandWinglessand the Cadherin family of cell‐cell adhesion molecules. The roles of stem cells and of mutations of thePatchedgene in epithelial carcinogenesis are disc

ISSN:0265-9247    

DOI:10.1002/bies.950190808

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

年代:1997

数据来源: WILEY

摘要:

AbstractSkin is one of the most thoroughly studied epithelia and can be used as a model for transcriptional control of epithelial differentiation. In particular, the stages of epidermal development and differentiation from a simple epithelium are well characterized. Temporal gene expression during development can be used to assign roles for transcription factors in epidermal differentiation. Approaches to understanding transcriptional regulation in epidermis include extensive promoter analysis and expression studies, in some cases coupled to functional studies. This work has not produced any consensus about the importance of any particular factor or class of factors in epidermal specification. There is, as yet, nothing similar to the myo D family of tissue‐specific and cell‐type determining factors in epidermis. These studies, however, have revealed much about control of the differentiation process in epidermis. Most recently, there has been a suggestion that epithelial transcription can be influenced directly by the status of the adhesion complexes at the cell surface, providing a direct link between one of the distinguishing features of the epithelial state and gene transcript

ISSN:0265-9247    

DOI:10.1002/bies.950190809

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

年代:1997

数据来源: WILEY

摘要:

AbstractEpithelia can be defined morphologically as tissues that line surfaces, and ultrastructurally with reference to their cells' apico‐basal polarity and possession of specific cell‐cell junctions. Defining the epithelial phenotype at a molecular level is more problematic ‐ while it is easy to name proteins (e.g. keratins) expressed by a “typical” epithelium, no known molecules are expressed by every epithelium but by no other tissues. Cells can differentiate to and from the epithelial state as part of normal development, as a response to disease or when manipulated in culture. Many factors (matrix components, adhesion molecules, growth factors, transcription factors) have been identified that can trigger these transitions of phenotype in specific cases, but to date no general master regulators of the epithelial state have been found. The epithelial state may therefore be controlled by multiple regulatory genes so that there is no single molecule responsible for all of the diverse types of epithelium that exist in highe

ISSN:0265-9247    

DOI:10.1002/bies.950190810

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

年代:1997

数据来源: WILEY

摘要:

AbstractThe expression of epithelial cell adhesion and cytoskeletal genes is orchestrated by an apparently unique set of rules. No tissue‐specific transactivator proteins have been found to drive them; only ubiquitous factors are utilized. In non‐epithelial cells, they are actively repressed. Moreover, it was recently found that a single protein (adenovirus E1a) coordinately represses non‐epithelial genes while inducing epithelial genes. A simple model is offered to explain how epithelial gene expression is coordinated. Under this model, the epithelial cell gene expression program is a transcriptional ‘default’; that is, it occurs in the absence of tissue‐specific transactivation. Conversion to this default requires only that mesenchymal transactivators are not expressed, or that central ‘integrator’ proteins are inactive. In their absence, mesenchymal gene expression cannot occur. Moreover, because the repressors cease to be expressed, the epithelial genes are induced. Oncogenes generally cause the breakdown of the epithelial phenotype ‐ generating carcinomas ‐ so genes such as E1a that cause epithelial conversion may prove useful for both understanding and

ISSN:0265-9247    

DOI:10.1002/bies.950190811

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

年代:1997

数据来源: WILEY