bluuebunny/crossref_metadata_2025 huggingface dataset:
Gene therapy: prospects for glycolipid storage diseases
Authors: Gieselmann Volkmar , Matzner Ulrich , Klein Diana , Eric Mansson Jan , D'Hooge Rudi , DeDeyn Peter D. , Lüllmann Rauch Renate , Hartmann Dieter , Harzer Klaus
Published: September 2003

Lysosomal storage diseases comprise a group of about 40 disorders, which in most cases are due to the deficiency of a lysosomal enzyme. Since lysosomal enzymes are involved in the degradation of various compounds, the diseases can be further subdivided according to which pathway is affected. Thus, enzyme deficiencies in the degradation pathway of glycosaminoglycans cause mucopolysaccharidosis, and deficiencies affecting glycopeptides cause glycoproteinosis. In glycolipid storage diseases enzymes are deficient that are involved in the degradation of sphingolipids. Mouse models are available for most of these diseases, and some of these mouse models have been used to study the applicability of
in vivo
gene therapy. We review the rationale for gene therapy in lysosomal disorders and present data, in particular, about trials in an animal model of metachromatic leukodystrophy. The data of these trials are compared with those obtained with animal models of other lysosomal diseases.
Small–molecule therapeutics for the treatment of glycolipid lysosomal storage disorders
Authors: Butters Terry D. , Mellor Howard R. , Narita Keishi , Dwek Raymond A. , Platt Frances M.
Published: September 2003

Glycosphingolipid (GSL) lysosomal storage disorders are a small but challenging group of human diseases to treat. Although these disorders appear to be monogenic in origin, where the catalytic activity of enzymes in GSL catabolism is impaired, the clinical presentation and severity of disease are heterogeneous. Present attitudes to treatment demand individual therapeutics designed to match the specific disease–related gene defect; this is an acceptable approach for those diseases with high frequency, but it lacks viability for extremely rare conditions.

An alternative therapeutic approach termed ‘substrate deprivation’ or ‘substrate reduction therapy’ (SRT) aims to balance cellular GSL biosynthesis with the impairment in catalytic activity seen in lysosomal storage disorders. The development of N–alkylated iminosugars that have inhibitory activity against the first enzyme in the pathway for glucosylating sphingolipid in eukaryotic cells, ceramide–specific glucosyltransferase, offers a generic therapeutic for the treatment of all glucosphingolipidoses. The successful use of N–alkylated iminosugars to establish SRT as an alternative therapeutic strategy has been demonstrated in
in vitro
,
in vivo
and in clinical trials for type 1 Gaucher disease. The implications of these studies and the prospects of improvement to the design of iminosugar compounds for treating Gaucher and other GSL lysosomal storage disorders will be discussed.
Substrate reduction therapy in mouse models of the glycosphingolipidoses
Authors: Platt Frances M. , Jeyakumar Mylvaganam , Andersson Ulrika , Heare Tanya , Dwek Raymond A. , Butters Terry D.
Published: September 2003

Substrate reduction therapy uses small molecules to slow the rate of glycolipid biosynthesis. One of these drugs,
N
–butyldeoxynojirimycin (NB–DNJ), shows efficacy in mouse models of Tay–Sachs, Sandhoff and Fabry diseases. This offers the prospect that NB–DNJ may be of therapeutic benefit, at least in the juvenile and adult onset variants of these disorders. The infantile onset variants will require an additional enzyme–augmenting modality if the pathology is to be significantly improved. A second drug,
N
–butyldeoxyglactonojirimycin, looks very promising for treating storage diseases with neurological involvement as high systemic dosing is achievable without any side–effects.
A historical perspective of the glycosphingolipids and sphingolipidoses
Authors: Watts Richard W. E.
Published: September 2003

Glycosphingolipids are a polysaccharide chain between 1 and 40 carbohydrate residues long glycosidically linked to ceramide (a long–chain aliphatic amino–alcohol or sphingoid) that is embedded in the cell plasma membrane with the carbohydrate moiety on the outside. The sphingoid imparts rigidity to the membrane and the carbohydrate tails protect the cell surface and have functions in relation to cell adhesion, growth, regulation, differentiation, cell interaction, recognition and signalling. They provide adhesion sites for pathogens and change during oncogenic transformation. Ceramide is also a component of sphingomyelin. Glycosphingolipids are degraded by lysosomal hydrolysis. The sphingolipidoses are a series of diseases in which mutations affecting the enzymes catalysing the last 11 steps of this process causing abnormal compounds proximal to the metabolic block to accumulate intralysosomally. Thus, they are a sub–group of the lysosomal storage diseases. The degradation of sphingolipids containing three or less carbohydrate residues requires a sphingolipid activator protein and mutations affecting these proteins also cause abnormal glycosphingolipid storage.

With one exception (Fabry disease, which is X linked) the sphingolipidoses are inherited autosomally. The phenotypic manifestations of the individual sphingolipidoses are variable although the more severe variants are usually the better known. They have generally been regarded as untreatable but notable therapeutic advances are being made by enzyme replacement therapy and regulating the rate of glycosphingolipid synthesis by inhibiting UDP–glucose–
N
–acylsphingosine D–glucosyl transferase (CerGlcT), which is the first reaction on the pathway of glycosphingolipid synthesis. The compounds used are N–alkylated iminosugars whose glucose and galactose stereochemistries inhibit CerGlcT.

Prenatal and carrier state diagnosis, genetic counselling and the abortion of affected foetuses are reducing the incidence of some of the most severe sphingolipidoses in certain high–incidence populations.
Introduction
Authors: Dwek Raymond A. , Butters Terry D. , Platt Frances M. , Cox Timothy M.
Published: September 2003

In an era dominated by molecular biology, genomics and proteomics it is perhaps not surprising that a relatively small number of scientists worldwide have focused their research on an obscure family of glycoconjugates known as the glycosphingolipids. At first glance, these molecules have very little to commend them; they are complex and variable, not abundant in relation to other cellular lipids, are the product of multi–gene pathways making them hard to manipulate, are not trivial to purify or characterize and the technologies to analyse them have traditionally been insensitive and cumbersome. To compound the problem, we do not fully understand the role they play in cells let alone how they contribute to homeostasis in the intact organism. Theories abound but, until recently, hard evidence has been lacking. For decades they have therefore been a minority interest overlooked by the majority of investigators in both the biological and biomedical sciences.
The genetic architecture necessary for transgressive segregation is common in both natural and domesticated populations
Authors: Rieseberg Loren H. , Widmer Alex , Arntz A. Michele , Burke Burke
Published: September 2003

Segregating hybrids often exhibit phenotypes that are extreme or novel relative to the parental lines. This phenomenon is referred to as transgressive segregation, and it provides a mechanism by which hybridization might contribute to adaptive evolution. Genetic studies indicate that transgressive segregation typically results from recombination between parental taxa that possess quantitative trait loci (QTLs) with antagonistic effects (i.e. QTLs with effects that are in the opposite direction to parental differences for those traits). To assess whether this genetic architecture is common, we tabulated the direction of allelic effects for 3252 QTLs from 749 traits and 96 studies. Most traits (63.6%) had at least one antagonistic QTL, indicating that the genetic substrate for transgressive segregation is common. Plants had significantly more antagonistic QTLs than animals, which agrees with previous reports that transgressive segregation is more common in plants than in animals. Likewise, antagonistic QTLs were more frequent in intra– than in interspecific crosses and in morphological than in physiological traits. These results indicate that transgressive segregation provides a general mechanism for the production of extreme phenotypes at both above and below the species level and testify to the possible creative part of hybridization in adaptive evolution and speciation.
The
S
–locus and unilateral incompatibility
Authors: Hancock C. Nathan , Kondo Katsuhiko , Beecher Brian , McClure Bruce
Published: September 2003

Plants have many ways to regulate the type of pollen that arrives on the stigma surface. Once there, further control mechanisms regulate compatibility. The latter controls are largely based on biochemical interactions that support compatible pollination and prevent incompatible matings. S–RNase–based self–incompatibility (SI) systems are the most phylogenetically widespread mechanisms for controlling pollination. Studies of
Nicotiana
establish a firm link between SI and unilateral interspecific incompatibility. Although implicated in both inter– and intraspecific compatibility, S–RNase operates through at least three distinct genetic mechanisms that differ in their dependence on non–S–RNase factors. Identification and characterization of these non–S–RNase factors is currently an area of active research. Searching for genetic and biochemical interactions with S–RNase can identify candidate non–S–RNase factors. HT–protein is one factor that is required for
S
–allele–specific pollen rejection in the Solanaceae. Major style arabinogalactan proteins such as TTS interact biochemically with S–RNase. These glycoproteins are known to interact with compatible pollen tubes and have long been suggested as possible recognition molecules. Their binding to S–RNase implies a link between stylar systems for compatibility and incompatibility. Thus, genetic and biochemical studies suggest a highly networked picture of pollen–pistil interactions.
Male and female synchrony and the regulation of mating in flowering plants
Authors: Herrero M.
Published: September 2003

Successful mating clearly requires synchronous development of the male and female sexual organs. Evidence is accumulating that this synchrony of development also persists after pollination, with both pollen and pistil following complex, but highly integrated developmental pathways. The timing of the male–female interaction is crucial for the pistil, which, far from being a mature passive structure, is engaged in a continuing programme of development: only being receptive to the advances of the pollen for a relatively short window of time. This developmental programme is most conspicuous in the ovary, and this review focuses on the interaction between the male and female tissues in this structure. The review first considers pollen tube development in the ovary, concentrating of the mechanisms by which its growth is modulated at various control points associated with structures within the ovary. Second, alterations to this ‘normal’ developmental programme are reviewed and considered in the context of a breakdown of developmental synchrony. Finally, the consequences of male–female developmental synchrony and asynchrony are explored. Clearly, a synchronous male–female relationship leads to a successful fertilization. However, lack of synchrony also occurs, and could emerge as a powerful tool to investigate the regulation of mating.
Towards the theory of pollinator–mediated gene flow
Authors: Cresswell James E.
Published: September 2003

I present a new exposition of a model of gene flow by animal–mediated pollination between a source population and a sink population. The model's parameters describe two elements: (i) the expected portion of the source's paternity that extends to the sink population; and (ii) the dilution of this portion by within–sink pollinations. The model is termed the portion–dilution model (PDM). The PDM is a parametric restatement of the conventional view of animal–mediated pollination. In principle, it can be applied to plant species in general. I formulate a theoretical value of the portion parameter that maximizes gene flow and prescribe this as a benchmark against which to judge the performance of real systems. Existing foraging theory can be used in solving part of the PDM, but a theory for source–to–sink transitions by pollinators is currently elusive.
Investigating mechanisms involved in the self–incompatibility response in
Papaver rhoeas
Authors: Thomas Steve , Osman Kim , de Graaf Barend H. J. , Shevchenko Galina , Wheeler Mike , Franklin Chris (F. C. H.) , Franklin-Tong Noni (V. E.)
Published: September 2003

Sexual reproduction in flowering plants is controlled by recognition mechanisms involving the male gametophyte (the pollen) and the female sporophyte (the pistil). Self–incompatibility (SI) involves the recognition and rejection of self– or incompatible pollen by the pistil. In
Papaver rhoeas
, SI uses a Ca
2+
–based signalling cascade triggered by the
S
–protein, which is encoded by the stigmatic component of the
S
–locus. This results in the rapid inhibition of incompatible pollen tube growth. We have identified several targets of the SI signalling cascade, including protein kinases, the actin cytoskeleton and nuclear DNA. Here, we summarize progress made on currently funded projects in our laboratory investigating some of the components targeted by SI, comprising (i) the characterization of a pollen phosphoprotein (p26) that is rapidly phosphorylated upon an incompatible SI response; (ii) the identification and characterization of a pollen mitogen–activated protein kinase (p56), which exhibits enhanced activation during SI; (iii) characterizing components involved in the reorganization and depolymerization of the actin cytoskeleton during the SI response; and (iv) investigating whether the SI response involves a programmed cell death signalling cascade.
Plant introductions, hybridization and gene flow
Authors: Abbott Richard J. , James Juliet K. , Milne Richard I. , Gillies Amanda C. M.
Published: September 2003

Many regional floras contain a high proportion of recently introduced plant species. Occasionally, hybridization between an introduced species and another species (introduced or native) can result in interspecific gene flow. This may occur even in instances where the F1hybrid shows very high sterility, but occasionally produces a few viable gametes. We provide examples of gene flow occurring between some rhododendrons recently introduced to the British flora, and between an introduced and nativeSeneciospecies. Neutral molecular markers have normally been employed to obtain evidence of interspecific gene flow, but the challenge now is to isolate and characterize functional introgressed genes and to determine how they affect the fitness of introgressants and whether they improve adaptation to novel habitats allowing introgressants to expand the range of a species. We outline a candidate gene approach for isolating and characterizing an allele of theRAYgene inSenecio vulgaris, which is believed to have introgressed fromS. squalidus, and which causes the production of ray florets in flower heads. We discuss the effects of this introgressed allele on individual fitness, including those that originate directly from the production of ray florets plus those that may arise from pleiotropy and/or linkage.
Pollen performance before and during the autotrophic–heterotrophic transition of pollen tube growth
Authors: Stephenson Andrew G. , Travers Steven E. , Mena-Ali Jorge I. , Winsor James A.
Published: September 2003

For species with bicellular pollen, the attrition of pollen tubes is often greatest where the style narrows at the transition between stigmatic tissue and the transmitting tissue of the style. In this region, the tubes switch from predominantly autotrophic to predominantly heterotrophic growth, the generative cell divides, the first callose plugs are produced, and, in species with RNase–type self–incompatibility (SI), incompatible tubes are arrested. We review the literature and present new findings concerning the genetic, environmental and stylar influences on the performance of pollen before and during the autotrophic–heterotrophic transition of pollen tube growth. We found that the ability of the paternal sporophyte to provision its pollen during development significantly influences pollen performance during the autotrophic growth phase. Consequently, under conditions of pollen competition, pollen selection during the autotrophic phase is acting on the phenotype of the paternal sporophyte. In a field experiment, usingCucurbita pepo, we found broad–sense heritable variation for herbivore–pathogen resistance, and that the most resistant families produced larger and better performing pollen when the paternal sporophytes were not protected by insecticides, indicating that selection during the autotrophic phase can act on traits that are not expressed by the microgametophyte. In a study of a weedy SI species,Solanum carolinense, we found that the ability of the styles to arrest self–pollen tubes at the autotrophic–heterotrophic transition changes with floral age and the presence of developing fruits. These findings have important implications for selection at the level of the microgametophyte and the evolution of mating systems of plants.
Imprinting in the endosperm: a possible role in preventing wide hybridization
Authors: Gutierrez-Marcos Jose F. , Pennington Paul D. , Costa Liliana M. , Dickinson Hugh G.
Published: September 2003

Reproductive isolation is considered to play a key part in evolution, and plants and animals have developed a range of strategies that minimize gene flow between species. In plants, these strategies involve either pre–zygotic barriers, such as differences in floral structure and pollen–stigma recognition, or post–zygotic barriers, which are less well understood and affect aspects of seed development ranging from fertilization to maturation.

In most angiosperms, a double fertilization event gives rise to a zygote and the endosperm: a triploid tissue with an unequal parental genomic contribution, which, like the placenta of mammals, provides reserves to the developing embryo. Interestingly, many aspects of endosperm development, again like the placenta, are regulated by a range of epigenetic mechanisms that are globally termed imprinting. Imprinted genes are characterized by their uniparental expression, the other parental allele being silenced. Normal development of the endosperm thus requires a highly specific balance of gene expression, from either the maternal or paternal genomes. Any alteration of this balance resulting from changes in allelic copy number, sequence or epigenetic imprints can cause endosperm failure and eventual seed abortion. In its widest sense, the endosperm thus serves as an accurate ‘sensor’ of compatibility between parents. A first step in understanding this important, yet complex system must clearly be the isolation and characterization of as wide a range as possible of imprinted genes.
Using empirical data to model transgene dispersal
Authors: Meagher T. R. , Belanger F. C. , Day P. R.
Published: September 2003

One element of the current public debate about genetically modified crops is that gene flow from transgenic cultivars into surrounding weed populations will lead to more problematic weeds, particularly for traits such as herbicide resistance. Evolutionary biologists can inform this debate by providing accurate estimates of gene flow potential and subsequent ecological performance of resulting hybrids. We develop a model for gene flow incorporating exponential distance and directional effects to be applied to windpollinated species. This model is applied to previously published data on gene flow in experimental plots ofAgrostis stoloniferaL. (creeping bentgrass), which assessed gene flow from transgenic plants resistant to the herbicide glufosinate to surrounding non–transgenic plants. Our results show that although pollen dispersal can be limited in some sites, it may be extensive in others, depending on local conditions such as exposure to wind. Thus, hybridization under field conditions is likely to occur. Given the nature of the herbicide resistance trait, we regard this trait as unlikely to persist in the absence of herbicide, and suggest that the ecological consequences of such gene flow are likely to be minimal.
Apomixis in flowering plants: an overview
Authors: Richards A. J.
Published: September 2003

Apomixis is a common feature of perennial plants, which occurs inca. 60% of the British flora, but has been largely ignored by reproductive theoreticians. Successful individuals may cover huge areas, and live to great ages, favoured by ‘symmetrical’ selection. Apomixis is favoured by colonizing modes, for instance post–glacially. Despite its theoretical advantages, apomixis usually coexists with sexuality, suggesting ‘hidden’ disadvantages. Agamospermy (apomixis by seed) is relatively uncommon, but gains from the attributes of the seed. It pays agamospermy genes, which discourage recombination, to form co–adapted linkage groups, so that they become targets for disadvantageous recessive mutant accumulation. Consequently, agamospermy genes cannot succeed in diploids and agamosperms are hybrid and highly heterotic. Agamospermous endosperm may suffer from genomic imbalance, so that nutritious ovules, which can support embryos without endosperm, may be preadapted for agamospermy. When primary endosperm nucleus fertilization (‘pseudogamy’) continues as a requirement for many aposporous agamosperms, selfing sex becomes preadaptive and archesporial sex remains an option. Apomictic populations can be quite variable although apomictic families are much less variable than sexuals. Only in some diplosporous species does sex disappear completely, and in those species some release of variability may persist through somatic recombination. The search for an agamospermy gene suitable for genetic modification should target fertile sexuals with a single localized agamospermy (A) gene, which therefore lack a genetic load. TheAgene should coexist alongside sexuality, so that it would be easy to select seedlings of sexual and asexual origins. Plants with sporophytic agamospermy provide all these attributes.
Recent approaches into the genetic basis of inbreeding depression in plants
Authors: Carr David E. , Dudash Michele R.
Published: September 2003

Predictions for the evolution of mating systems and genetic load vary, depending on the genetic basis of inbreeding depression (dominance versus overdominance, epistasis and the relative frequencies of genes of large and small effect). A distinction between the dominance and overdominance hypotheses is that deleterious recessive mutations should be purged in inbreeding populations. Comparative studies of populations differing in their level of inbreeding and experimental approaches that allow selection among inbred lines support this prediction. More direct biometric approaches provide strong support for the importance of partly recessive deleterious alleles. Investigators using molecular markers to study quantitative trait loci (QTL) often find support for overdominance, though pseudo–overdominance (deleterious alleles linked in repulsion) may bias this perception. QTL and biometric studies of inbred lines often find evidence for epistasis, which may also contribute to the perception of overdominance, though this may be because of the divergent lines initially crossed in QTL studies. Studies of marker segregation distortion commonly uncover genes of major effect on viability, but these have only minor contributions to inbreeding depression. Although considerable progress has been made in understanding the genetic basis of inbreeding depression, we feel that all three aspects merit more study in natural plant populations.
Effects of inbreeding on the genetic diversity of populations
Authors: Charlesworth Deborah
Published: September 2003

The study of variability within species is important to all biologists who use genetic markers. Since the discovery of molecular variability among normal individuals, data have been collected from a wide range of organisms, and it is important to understand the major factors affecting diversity levels and patterns. Comparisons of inbreeding and outcrossing populations can contribute to this understanding, and therefore studying plant populations is important, because related species often have different breeding systems. DNA sequence data are now starting to become available from suitable plant and animal populations, to measure and compare variability levels and test predictions.
The different mechanisms of sporophytic self–incompatibility
Authors: Hiscock Simon J. , Tabah David A.
Published: September 2003

Flowering plants have evolved a multitude of mechanisms to avoid self–fertilization and promote outbreeding. Self–incompatibility (SI) is by far the most common of these, and is found inca. 60% of flowering plants. SI is a genetically controlled pollen–pistil recognition system that provides a barrier to fertilization by self and self–related pollen in hermaphrodite (usually co–sexual) flowering plants. Two genetically distinct forms of SI can be recognized: gametophytic SI (GSI) and sporophytic SI (SSI), distinguished by how the incompatibility phenotype of the pollen is determined. GSI appears to be the most common mode of SI and can operate through at least three different mechanisms, two of which have been characterized extensively at a molecular level in the Solanaceae and Papaveraceae. Because molecular studies of SSI have been largely confined to species from the Brassicaceae, predominantlyBrassicaspecies, it is not yet known whether SSI, like GSI, can operate through different molecular mechanisms. Molecular studies of SSI are now being carried out onIpomoea trifida(Convolvulaceae) andSenecio squalidus(Asteraceae) and are providing important preliminary data suggesting that SSI in these two families does not share the same molecular mechanism as that of the Brassicaceae. Here, what is currently known about the molecular regulation of SSI in the Brassicaceae is briefly reviewed, and the emerging data on SSI inI. trifida, and more especially inS. squalidus, are discussed.
Genetic mechanisms of apomixis
Authors: Spielman Melissa , Vinkenoog Rinke , Scott Rod J.
Published: September 2003

The introduction of apomixis to crops would allow desirable genotypes to be propagated while preventing undesirable gene flow, but so far there has been little success in transferring this trait from a natural apomict to another species. One explanation is the sensitivity of endosperm to changes in relative maternal and paternal contribution owing to parental imprinting, an epigenetic system of transcriptional regulation by which some genes are expressed from only the maternally or paternally contributed allele. In sexual species, endosperm typically requires a ratio of two maternal genomes to one paternal genome for normal development, but this ratio is often altered in apomicts, suggesting that the imprinting system is altered as well. We present evidence that modification of DNA methylation is one mechanism by which the imprinting system could be altered to allow endosperm development in apomicts. Another feature of natural apomixis is the modification of the normal fertilization programme. Sexual reproduction uses both sperm from each pollen grain, but pseudogamous apomicts, which require a sexual endosperm to support the asexual embryo, often use just one. We present evidence that multiple fertilization of the central cell is possible inArabidopsis thaliana, suggesting that pseudogamous apomicts may also need to acquire a mechanism for preventing more than one sperm from contributing to the endosperm. We conclude that strategies to transfer apomixis to crop species should take account of endosperm development and particularly its sensitivity to parental imprinting, as well as the mechanism of fertilization.
Current knowledge of gene flow in plants: implications for transgene flow
Authors: Ellstrand Norman C.
Published: September 2003

Plant evolutionary biologists' view of gene flow and hybridization has undergone a revolution. Twenty–five years ago, both were considered rare and largely inconsequential. Now gene flow and hybridization are known to be idiosyncratic, varying with the specific populations involved. Gene flow typically occurs at evolutionarily significant rates and at significant distances. Spontaneous hybridization occasionally has important applied consequences, such as stimulating the evolution of more aggressive invasives and increasing the extinction risk for rare species. The same problems have occurred for spontaneous hybridization between crops and their wild relatives. These new data have implications for transgenic crops: (i) for most crops, gene flow can act to introduce engineered genes into wild populations; (ii) depending on the specific engineered gene(s) and populations involved, gene flow may have the same negative impacts as those observed for traditionally improved crops; (iii) gene flow's idiosyncratic nature may frustrate management and monitoring attempts; and (iv) intercrop transgene flow, although rarely discussed, is equally worthy of study.
The population genetics of sporophytic self–incompatibility inSenecio squalidusL. (Asteraceae): avoidance of mating constraints imposed by lowS–allele number
Authors: Brennan Adrian C. , Harris Stephen A. , Hiscock Simon J.
Published: September 2003

Senecio squalidusL. (Asteraceae) has been the subject of several ecological and population genetic studies due to its well–documented history of introduction, establishment and spread throughout Britain in the past 300 years. Our recent studies have focused on identifying and quantifying factors associated with the sporophytic self–incompatibility (SSI) system ofS. squalidusthat may have contributed to its success as a colonist. These findings are of general biological interest because they provide important insights into the short–term evolutionary dynamics of a plant mating system. The number ofS–alleles in populations and their dominance interactions were investigated in eight wild British populations using cross–diallel studies. The numbers ofS–alleles in BritishS. squaliduspopulations are typically low (average of 5.3S–alleles) and the entire British population is estimated to possess no more than 7–11S–alleles. Such low numbers ofS–alleles are most probably a consequence of population bottlenecks associated with introduction and colonization. Potential evolutionary impacts on SSI caused by a paucity ofS–alleles, such as restricted mate availability, are discussed, and we suggest that increased dominance interactions betweenS–alleles may be an important short–term means of increasing mate availability whenS–allele numbers are low.
Mating strategies in flowering plants: the outcrossing–selfing paradigm and beyond
Authors: Barrett Spencer C. H.
Published: September 2003

Comparisons of the causes and consequences of cross– and self–fertilization have dominated research on plant mating since Darwin's seminal work on plant reproduction. Here, I provide examples of these accomplishments, but also illustrate new approaches that emphasize the role of floral design and display in pollen dispersal and fitness gain through male function. Wide variation in outcrossing rate characterizes animal–pollinated plants. In species with large floral displays, part of the selfing component of mixed mating can arise from geitonogamy and be maladaptive because of strong inbreeding depression and pollen discounting. Floral strategies that separate the benefits of floral display from the mating costs associated with geitonogamy can resolve these conflicts by reducing lost mating opportunities through male function. The results from experiments with marker genes and floral manipulations provide evidence for the function of herkogamy and dichogamy in reducing self–pollination and promoting pollen dispersal. Evidence is also presented indicating that increased selfing resulting from changes to floral design, or geitonogamy in large clones, can act as a stimulus for the evolution of dioecy. The scope of future research on mating strategies needs to be broadened to include investigations of functional links among flowers, inflorescences and plant architecture within the framework of life–history evolution.
Do the different parental ‘heteromes’ cause genomic shock in newly formed allopolyploids?
Authors: Comai Luca , Madlung Andreas , Josefsson Caroline , Tyagi Anand
Published: September 2003

Allopolyploidy, the joining of two parental genomes in a polyploid organism with diploid meiosis, is an important mechanism of reticulate evolution. While many successful long–established allopolyploids are known, those formed recently undergo an instability phase whose basis is now being characterized. We describe observations made with theArabidopsissystem that include phenotypic instability, gene silencing and activation, and methylation changes. We present a model based on the epigenetic destabilization of genomic repeats, which in the parents are heterochromatinized and suppressed. We hypothesize that loss of epigenetic suppression of these sequences, here defined as the heterome, results in genomic instability including silencing of single–copy genes.
The emergence of abstract ideas: evidence from networks and babies
Authors: Colung Eliana , Smith Linda B.
Published: September 2003

What is abstraction? In our view, abstraction is generalization. Specifically, we propose that abstract concepts emerge as the natural product of associative learning and generalization by similarity. We support this proposal by presenting evidence for two ideas: first, that children's knowledge about how categories are organized and how words refer to them can be explained as learned generalizations over specific experiences of words referring to categories; and second, that the path of concepts from concrete to more abstract can be observed throughout development and that even in their more abstract form, concepts retain some of their original sensory basis. We illustrate these two facts by examining, in two kinds of learners—networks and young children—the development of three abstract ideas: (i) the idea of word; (ii) the idea of object; and (iii) the idea of substance.
Abstraction in art with implications for perception
Authors: Zimmer Robert
Published: September 2003

The relationship between people and art is complex and intriguing. Of course, artworks are our creations; but in interesting and important ways, we are also created by our artworks. Our sense of the world is informed by the art we make and by the art we inherit and value, works that, in themselves, encode others' world views. This two-way effect is deeply rooted and art encodes and affects both a culture's ways of perceiving the world and its ways of remaking the world it perceives. The purpose of this paper is to indicate ways in which a study of abstraction in art can be used to discover insights into, to quote the call for papers for this issue, ‘our perception of the world, acquired through experience’ and ‘the way concepts are formed and manipulated to achieve goals’.
A grounded theory of abstraction in artificial intelligence
Authors: Zucker Jean-Daniel
Published: September 2003

In artificial intelligence, abstraction is commonly used to account for the use of various levels of details in a given representation language or the ability to change from one level to another while preserving useful properties. Abstraction has been mainly studied in problem solving, theorem proving, knowledge representation (in particular for spatial and temporal reasoning) and machine learning. In such contexts, abstraction is defined as a mapping between formalisms that reduces the computational complexity of the task at stake. By analysing the notion of abstraction from an information quantity point of view, we pinpoint the differences and the complementary role of reformulation and abstraction in any representation change. We contribute to extending the existing semantic theories of abstraction to be grounded on perception, where the notion of information quantity is easier to characterize formally. In the author's view, abstraction is best represented using abstraction operators, as they provide semantics for classifying different abstractions and support the automation of representation changes. The usefulness of a grounded theory of abstraction in the cartography domain is illustrated. Finally, the importance of explicitly representing abstraction for designing more autonomous and adaptive systems is discussed.
Abstraction and art
Authors: Gortais Bernard
Published: September 2003

In a given social context, artistic creation comprises a set of processes, which relate to the activity of the artist and the activity of the spectator. Through these processes we see and understand that the world is vaster than it is said to be. Artistic processes are mediated experiences that open up the world. A successful work of art expresses a reality beyond actual reality: it suggests an unknown world using the means and the signs of the known world. Artistic practices incorporate the means of creation developed by science and technology and change forms as they change. Artists and the public follow different processes of abstraction at different levels, in the definition of the means of creation, of representation and of perception of a work of art. This paper examines how the processes of abstraction are used within the framework of the visual arts and abstract painting, which appeared during a period of growing importance for the processes of abstraction in science and technology, at the beginning of the twentieth century. The development of digital platforms and new man–machine interfaces allow multimedia creations. This is performed under the constraint of phases of multidisciplinary conceptualization using generic representation languages, which tend to abolish traditional frontiers between the arts: visual arts, drama, dance and music.
Visual categorization: accessing abstraction in non–human primates
Authors: Fabre-Thorpe Michèle
Published: September 2003

Evolution might have set the basic foundations for abstract mental representation long ago. Because of language, mental abilities would have reached different degrees of sophistication in mammals and in humans but would be, essentially, of the same nature. Thus, humans and animals might rely on the same basic mechanisms that could be masked in humans by the use of sophisticated strategies. In this paper, monkey and human abilities are compared in a variety of perceptual tasks including visual categorization to assess behavioural similarities and dissimilarities, and to determine the level of abstraction of monkeys' mental representations. The question of how these abstract representations might be encoded in the brain is then addressed. A comparative study of the neural processing underlying abstract cognitive operations in animals and humans might help to understand when abstraction emerged in the phylogenetic scale, and how it increased in complexity.
Abstract and associatively based representations in human sequence learning
Authors: Spiegel Rainer , McLaren I. P. L.
Published: September 2003

We give an analysis of performance in an artificial neural network for which the claim had been made that it could learn abstract representations. Our argument is that this network is associative in nature, and cannot develop abstract representations. The network thus converges to a solution that is solely based on the statistical regularities of the training set. Inspired by human experiments that have shown that humans can engage in both associative (statistical) and abstract learning, we present a new, hybrid computational model that combines associative and more abstract, cognitive processes. To cross–validate the model we attempted to predict human behaviour in further experiments. One of these experiments reveals some evidence for the use of abstract representations, whereas the others provide evidence for associatively based performance. The predictions of the hybrid model stand in line with our empirical data.
Abstraction and natural language semantics
Authors: Kayser Daniel
Published: September 2003

According to the traditional view, a word prototypically denotes a class of objects sharing similar features, i.e. it results from an abstraction based on the detection of common properties in perceived entities. I explore here another idea: words result from abstraction of common premises in the rules governing our actions. I first argue that taking ‘inference’, instead of ‘reference’, as the basic issue in semantics does matter. I then discuss two phenomena that are, in my opinion, particularly difficult to analyse within the scope of traditional semantic theories: systematic polysemy and plurals. I conclude by a discussion of my approach, and by a summary of its main features.
Abstraction from a sensori-motor perspective: can we get a quick hold on simple perception?
Authors: Rossetti Yves
Published: September 2003

Two main types of dissociation can be considered in order to articulate action and abstraction. Vision for action and vision for perception are often described as dissociated systems at both anatomical and functional levels. Within this framework, abstraction should be specific to perceptual representation, whereas the action system would simply analyse the objective metric of space. By contrast, one may focus on dissociations within the action system. In this case, one will accept that action may involve abstract representations, at least during movement preparation. But a specific visuomotor level of processing can be described that appears to comply with the spatial properties of the relationship between the actor and the environment. This system would be specialized for fast movement guidance towards pre–defined goals. Such an automatic piloting system would thus be free of abstraction.
Abstraction and context in concept representation
Authors: Hampton James A.
Published: September 2003

This paper develops the notion of abstraction in the context of the psychology of concepts, and discusses its relation to context dependence in knowledge representation. Three general approaches to modelling conceptual knowledge from the domain of cognitive psychology are discussed, which serve to illustrate a theoretical dimension of increasing levels of abstraction.
A neuroscientific grasp of concepts: from control to representation
Authors: Gallese Vittorio
Published: September 2003

Abstraction denotes the cognitive process by means of which general concepts are formed. The dominant view of abstraction considers it not only as a complex and sophisticated cognitive activity, but also as a distinctive hallmark of mankind. The distinctiveness of abstract thought has indeed been closely related to another feature peculiar to our species: language. Following this perspective, the possibility to entertain conceptual representations is thus precluded to animals devoid of full–blown language. I challenge this view and propose that the representational dynamic of the brain is conceivable as a type of self–organization, in which action plays a crucial part. My aim will be to investigate whether, and to what extent, conceptual knowledge can be attributed to non–linguistic animal species, with particular emphasis on nonhuman primates. I therefore introduce the notion of semantic content as a type of ‘relational specification’. A review of recent neurophysiological data on the neural underpinnings of action end–states in the macaque monkey brain is presented. On the basis of this evidence, I propose that conceptual representations can be conceived as the expression of a coherent internal world model. This model decomposes the ‘outer’ space inhabited by things in a meaningful way only to the extent that it accords to biologically constrained, embodied invariance. Finally, I discuss how the ‘comparative’ neuroscientific approach to abstraction proposed here may shed some light on its nature and its evolutionary origin.
Abstraction in mathematics
Authors: Ferrari Pier Luigi
Published: September 2003

Some current interpretations of abstraction in mathematical settings are examined from different perspectives, including history and learning. It is argued that abstraction is a complex concept and that it cannot be reduced to generalization or decontextualization only. In particular, the links between abstraction processes and the emergence of new objects are shown. The role that representations have in abstraction is discussed, taking into account both the historical and the educational perspectives. As languages play a major role in mathematics, some ideas from functional linguistics are applied to explain to what extent mathematical notations are to be considered abstract. Finally, abstraction is examined from the perspective of mathematics education, to show that the teaching ideas resulting from one–dimensional interpretations of abstraction have proved utterly unsuccessful.
Abstraction and reformulation in artificial intelligence
Authors: Holte Robert C. , Choueiry Berthe Y.
Published: September 2003

This paper contributes in two ways to the aims of this special issue on abstraction. The first is to show that there are compelling reasons motivating the use of abstraction in the purely computational realm of artificial intelligence. The second is to contribute to the overall discussion of the nature of abstraction by providing examples of the abstraction processes currently used in artificial intelligence. Although each type of abstraction is specific to a somewhat narrow context, it is hoped that collectively they illustrate the richness and variety of abstraction in its fullest sense.
Beyond learning fixed rules and social cues: abstraction in the social arena
Authors: Call Josep
Published: September 2003

Abstraction is a central idea in many areas of physical comparative cognition such as categorization, numerical competence or problem solving. This idea, however, has rarely been applied to comparative social cognition. In this paper, I propose that the notion of abstraction can be applied to the social arena and become an important tool to investigate the social cognition and behaviour processes in animals. To make this point, I present recent evidence showing that chimpanzees know about what others can see and about what others intend. These data do not fit either low-level mechanisms based on stimulus-response associations or high-level explanations based on metarepresentational mechanisms such as false belief attribution. Instead, I argue that social abstraction, in particular the development of concepts such as seeing in others, is key to explaining the behaviour of our closest relative in a variety of situations.