摘要:

AbstractAgoutiexpression during the middle portion of the mouse hair growth cycle induces melanocytes to synthesize yellow instead of black pigment, generating black hairs with a yellow band. Dominantagoutialleles increase the amount of yellow pigment in the coat and are associated with pleiotropic effects including obesity, diabetes and increased tumor susceptibility. Four dominantagoutialleles (Aiapy,Aiy,AsyandAvy) were recently shown to result from insertions that cause ubiquitous expression of chimeric transcripts encoding a wild‐typeagoutiprotein(1,2). Three insertions were identified as intracisternal A‐particles, which helps explain the variable coat colors and parental imprinting effects associated with some dominatagoutialle

ISSN:0265-9247    

DOI:10.1002/bies.950161002

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe mechanisms used to establish embryonic polarity are still largely unknown. A recent paper(1)describes the expression pattern of the geneglp‐1, which is required for induction events during development of the nematodeCaenorhabditis elegans.Althoughglp‐1RNA is found throughout the early embryo, Glp‐1 protein is only expressed in anterior cells. This negative translational regulation in posterior cells is shown to be mediated through sequences in theglp‐13′ untranslated region (3′UTR). Thus in nematodes, as in Drosophila, translational repression is one mechanism used to establish the embryonic anterior‐p

ISSN:0265-9247    

DOI:10.1002/bies.950161003

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

年代:1994

数据来源: WILEY

摘要:

AbstractClassically, position effect variegation has been studied in Drosophila and results when a euchromatic gene is placed adjacent to either centromeric heterochromatin or to a telomeric domain. In such a circumstance expression of the locus variegates, being active in some cells and silent in others. Over the last few years a comparable phenomenon in yeast has been discovered. This system promises to tell us much about this curious behaviour. Indeed, experiments reported recently(1)indicate that the variegation of a yeast telomeric gene is cell‐cycle regulated. The results suggest the following model. During DNA replication there is a disassembly of chromatin that allows a competition between silencing factors andtrans‐activators to take place. Thus, reassembly of the domain may result in either the repression or the expression of the affected gene and, hence, produce a variegating phenot

ISSN:0265-9247    

DOI:10.1002/bies.950161004

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

年代:1994

数据来源: WILEY

摘要:

AbstractRecent work by Magnuson, Solomon and Grossman(1)adds to a growing body of evidence indicating that microorganisms possess sophisticated signaling systems that enable them to sense and respond to environmental challenges. Typically, this response results in morphological, physiological and even genetic differentiation, paralleling that observed among higher organisms. These signaling systems may be interpreted as adaptations that maximize the reproductive potential of a population.

ISSN:0265-9247    

DOI:10.1002/bies.950161005

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

年代:1994

数据来源: WILEY

摘要:

AbstractAncient DNA has been discovered in many types of preserved biological material, including bones, mummies, museum skins, insects in amber and plant fossils, and has become an important research tool in disciplines as diverse as archaeology, conservation biology and forensic science. In archaeology, ancient DNA can contribute both to the interpretation of individual sites and to the development of hypotheses about past populations. Site interpretation is aided by DNA‐based sex typing of fragmentary human bones, and by the use of genetic techniques to assess the degree of kinship between the remains of different individuals. On a broader scale, population migrations can be traced by studying genetic markers in ancient DNA, as in recent studies of the colonisation of the Pacific islands, while ancient DNA in preserved plant remains can provide information on the development of agricultur

ISSN:0265-9247    

DOI:10.1002/bies.950161006

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

年代:1994

数据来源: WILEY

摘要:

AbstractOrganelles transported along microtubules are normally moved to precise locations within cells. For example, synaptic vesiceles are transported to the neruronal synapse, the Golgi apparatus is generally found in a perinuclear location, and the membranes of the endoplasmic reticulum are actively extended to the cell periphery. The correct positioning of these organelles depends on microtubules and microtubule motors. Melanophores provide an extreme example of organized organelle transport. These cells are specialized to transport pigment granules, which are coordinately moved towards or away from the cell center, and result in the cell appearing alternately light or dark. Melanophores have proved to be an ideal system for studying the mechanisms by which the cell controls the direction of its organelle transport. Pigment granule dispersion (the movement away from the cell center) requires protein phosphorylation, while pigment aggregation (the movement towards the cell center) requires protein dephosphorylation. The target of this phosphorylation and dephosphorylation event is a protein that interacts with the microtubule motor protein, kinesin. Thus, the direction of organelle transport along microtubules may be regulated by controlling the activity of a microtubule motor.

ISSN:0265-9247    

DOI:10.1002/bies.950161007

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

年代:1994

数据来源: WILEY

摘要:

AbstractGlycine is a major inhibitory neurotransmitter in the spinal cord and in the brain stem, where it acts by activating a chloride conductance. The postsynaptic glycine receptor has been purified and contains two transmembrane subunits of 48 kDa (α) and 58 kDa (β), and a peripheral membrane protein of 93 kDa. cDNA sequencing of the α and β subunits has revealed a common structural organization and a strong homology between these polypeptides and the nicotinic acetylcholine and GABAAreceptor proteins. The glycine receptor exhibits a heterogeneity resulting from the existence of several α subtypes with distinct functional properties and different developmental expressions. When present in the central nervous systemin situ, as well as in primary cultures of spinal cord neurons, these receptors are localized at the postsynaptic membrane adjacent to the presynaptic release sites, thus forming functional microdomains at the neuronal surface. This distribution raises the question of the formation and the maintenance of the heterogeneity of the somato‐dendritic plasma me

ISSN:0265-9247    

DOI:10.1002/bies.950161008

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

年代:1994

数据来源: WILEY

摘要:

AbstractThere are many obvious morphological and behavioural differences between male and femaleDrosophila, whose differing phenotypes are produced by a hierarchy of sex determination genes. These genes have been well characterised at the genetic and molecular level. Similarly, a number of sex‐specific differentiation genes have been characterised, such as thechorionandvitelline membranegenes in females and thesex peptideand other accessory gland proteins in males. Despite the depth of these parallel studies, there is only one example of a direct link between the sex determination pathway and the downstream sex differentiation genes, namely the regulation of the female‐specific yolk protein genes. The yolk proteins are synthesised in the fat body and ovarian follicle cells of the adult female and are subsequently transported to the oocyte where they are stored for utilization during embrygenesis. The expression of the yolk protein genes is not entirely controlled by the sex determination hierarchy, as several different regulatory pathways must interact to direct their correct sexual, temporal and spatial regulation during developm

ISSN:0265-9247    

DOI:10.1002/bies.950161009

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe rate‐limiting step in the uptake and metabolism of Dglucose by insulin target cells is thought to be glucose transport mediated by glucose transporters (primarily the GLUT4 isoform) localized to the plasma membrane. However, subcellular fractionation, photolabelling and immunocytochemical studies have shown that the pool of GLUT4 present in the plasma membrane is only one of many subcellular pools of this protein. GLUT4 has been found in occluded vesicles at the plasma membrane, clathrin‐coated pits and vesicles, early endosomes, and tubulo‐vesicular structures; the latter are analogous to known specialized secretory compartments. Tracking the movement of GLUT4 through these compartments, and defining the mechanism and site of action of insulin in stimulating this subcellular trafficking, are major topics of current investigation. Recent evidence focuses attention on the exocytosis of GLUT4 as the major site of insulin action. Increased exocytosis may be due to decreased retention of glucose transporters in an intracellular pool, or possibly to increased assembly of a vesicle docking and fusion complex. Although details are unknown, the presence in GLUT4 vesicles of a synaptobrevin homologue leads us to propose that a process analogous to that occurring in synaptic vesicle trafficking is involved in the assembly of GLUT4 vesicles into a form suitable for fusion with the plasma membrane. Evidence that the pathways of signalling from the insulin receptor and of GLUT4 vesicle exocytosis may converge at the level of the key signalling enzyme, phosphatidylinositol 3‐kinase, is di

ISSN:0265-9247    

DOI:10.1002/bies.950161010

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

年代:1994

数据来源: WILEY

摘要:

AbstractEndo‐exonucleases fromE. colito man, although very different proteins, are multifunctional enzymes with similar enzymatic activities. They probably have two common but opposing biological roles. On the one hand, they promote survival of the organism by acting in recombination and recombinational DNA repair to diversify and help preserve the genome intact. On the other hand, they degrade the genomic DNA when it is damaged beyond repair. This ensures elimination of heavily mutagenized cells from the populatio

ISSN:0265-9247    

DOI:10.1002/bies.950161011

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

年代:1994

数据来源: WILEY