Encyclopedia of Life Sciences (ELS) - Free Content

Hair Cells

Hair cells are the sensory receptors in the inner ear that detect sound and head motion to begin the processes of hearing and balance control. The defining feature of hair cells is the hair bundle, the transduction organelle protruding from their apical surface composed of ordered arrays of stereocilia. Mechanical deflection of the hair bundle, normally induced by physiological stimuli, increases the open probability of mechanically gated cation channels located at the tip of stereocilia. The resulting depolarizing inward current generates a receptor potential. The information encoded in this electrical response is transmitted to the auditory or vestibular afferent nerve fibres via the Ca2+-induced release of neurotransmitter from the hair cell's basal pole. In this way sensory information is relayed to the brain enabling us to perceive sound and maintain balance. In mammals, hair cell loss causes irreversible balance and hearing impairment because these sensory cells show very little or no regenerative ability. Read full article

Liposomes

Liposomes are synthetic vesicles consisting of one or more phospholipid bilayers, able to accommodate water- and lipid-soluble molecules. They are used as a delivery system for drugs, genes and vaccines in therapeutics. Liposomes may be formulated with a range of characteristics including different size, charge and drug retention, which can be tailored for a given drug and target site. There is a range of clinical products approved for use which exploit liposomes to passively target drugs or vaccines to the appropriate site of action thereby improving specificity and reducing toxicity. Liposomes can also be actively targeted to specific cells or subcellular regions using targeting ligands attached to their surface, or by modification of the bilayer to give triggered release under appropriate conditions. Read full article

Politics in Biology

The relationship between biology and politics is manifold, ranging from politics within biology and implications of politics for biological research to intrinsic political dimensions of biological insights. Politics within biology plays out in the everyday practice of academic and applied science and has recently reached a new dimension in the context of priority and patent disputes, whereas political interventions in form of regulatory and funding policies have become major factors in shaping biological research. Here we focus on how the results of biology, and specifically modern evolutionary biology and its conceptual extensions, have shaped discussions in economics, medicine and public health and anthropology. We argue that these recent developments in the life sciences have enormous conceptual and practical implications for human society and politics as they contribute to a substantial reevaluation of some deeply entrenched conceptions about human nature and the foundations of society. Read full article

HPV Vaccine

The discovery in the early 1970s that cervical cancer was caused by infection with human papillomavirus (HPV) stimulated a highly successful vaccine development programme based on the use of recombinant deoxyribonucleic acid (DNA) technology to produce virus proteins in a form that can stimulate powerful and long lasting antibody responses. The vaccines have been designed as combinations to target the HPV virus types that are responsible for most human disease. Clinical trials have shown that it is possible to prevent both genital warts and the early stages of cervical cancer through vaccination and this has led to licensure and use of HPV vaccines in many countries throughout the world. Progression from initial virus infection to development of invasive cancer is often very slow, however, and so it will be many years before the impact of the vaccine on the overall disease burden is fully understood. Read full article

History of Ornithology

Before the seventeenth century, interest in birds centred largely on folklore and their symbolic significance. Ray and Willughby's encyclopaedia, the Ornithology of Francis Willughby (1676 and 1678) marked a turning point in the study of birds by rejecting folklore and focussing especially on biology. Following Ray's Wisdom of God (1691), which addressed ultimate causes, the study of birds developed along two separate strands: (i) systematics, nomenclature and faunistics (inspired by Ornithology) and (ii) natural history (inspired by Wisdom). The first of these endeavours dominated ornithology for the next 250 years, and were the main focus of the ornithological Unions founded in the 1800s. The two strands were reunited in the 1920s (central Europe) and 1940s (the UK and the USA). After World War II not only the expansion of higher education resulted in a huge increase in both the number of professional ornithologists, but also our knowledge of avian natural history and evolution. Read full article

Sjögren's Syndrome

Sjögren's syndrome is a lymphoproliferative disease with autoimmune features characterized by mononuclear cell infiltration of exocrine glands, notably the lacrimal and salivary glands (autoimmune exocrinopathy). These lymphoid infiltrations lead to dryness of the eyes (keratoconjunctivitis sicca), dryness of the mouth (xerostomia) and frequently, dryness of the nose, throat, vagina and skin. Sjögren's syndrome is associated with the production of autoantibodies because B-cell activation is a consistent immunoregulatory abnormality. The spectrum of the disease extends from an organ-specific autoimmune disorder to a systemic process (musculoskeletal, pulmonary, gastric, haematologic, dermatologic, renal and nervous system involvement). Sjögren's syndrome may occur alone (primary) or in association with almost any of the autoimmune rheumatic diseases (secondary), the most frequent being rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). Sjögren's syndrome also is associated with an increased risk of B-cell lymphoma development. Current treatments are mainly symptomatic. Read full article

Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis is a progressive neurodegenerative syndrome characterized by loss of motor neurons. Cognitive impairment occurs in a significant proportion of those affected. Numerous theories of pathogenesis have been advanced. The most cogent hypothesis is that genetic susceptibilities to neurodegeneration interact with environmental exposures, leading to neuronal injury, glial activation and neuronal death. Modern tools of molecular and cell biology and constructive international collaborations have provided insights into the factors that increase disease susceptibility. The important observation that genes associated with ribonucleic acid (RNA) processing are implicated in disease pathogenesis will undoubtedly influence the direction of research in the coming years. These factors, combined with improvements in clinical trial design, and an improved understanding of the limitations of translating positive findings from animal models to human subjects, are likely to lead to new and successful therapeutic options for patients in the near future. Read full article

Climate Change Impacts: Vegetation

Climate, more than any other factor, controls the broad-scale distributions of plant species and vegetation. Rapid climate change over the next century is likely to lead to major changes in the distribution of plants and thus in biomes and habitats. This will affect many other nonplant species as their ecology is intimately linked not only to climate but also to the habitat availability. How plants have already responded to climate change, concentrating on their phenology, the timing of events in their annual cycle such as leaf out or flowering and shifts in species ranges are summarized. How plants have responded in the past to changing climates particularly since the end of the last ice age is also discussed. Simulation modelling is a tool that is being used to forecast vegetation change and some of the techniques and forecasts for the future from modelling experiments are also described.

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Stable Isotope Ecology

Stable isotope geochemistry has proved to be an extremely useful tool in elucidating many ecological problems, with stable isotope ecology comprising the theme of a series of international conferences (http://www.isoecol.org). Stable isotopes can be used as biological tracers in the following ways: (i) to identify sources, for instance in determining the identity of basal carbon in a food web; (ii) to distinguish sources, for example to determine whether a breeding animal is using local resources or its own reserves; (iii) to quantify relative inputs in a system, for example determining the proportions of different prey items to a consumer's diet. When utilized carefully, stable isotope geochemistry provides some advantages over conventional methods, and provides an additional device for the ecologist. The following article provides a short reference for ecologists considering the inclusion of stable isotope analysis as part of their methodology. Read full article

Plant–Water Relations

Plant–water relations concern how plants control the hydration of their cells, including the collection of water from the soil, its transport within the plant and its loss by evaporation from the leaves. The water status of plants is usually expressed as ‘water potential’, which has units of pressure, is always negative, and in simple form is the algebraic sum of the hydrostatic pressure and the osmotic pressure of water. Flow of water through plant and soil over macroscopic distances is driven by gradients in hydrostatic pressure. Over microscopic distances (e.g. across semipermeable membranes) it is driven by gradients in water potential. Evaporation of water from leaves is primarily controlled by stomata, and if not made good by the flow of water from soil through the plant to the leaves, results in the plants wilting. Resistances to this flow are still not well understood. Read full article

Cancer Stem Cells

There is growing evidence that tumours display a hierarchy similar to normal tissues. A small population of cancer stem cells is supposed to perpetuate tumour growth. These cells self-renew and are highly tumourigenic upon injection into immunocompromised animals, yielding tumours largely identical to those from which they were derived.  In a recent article, Jiri Hatana and Wolfgang Shultz describe how a number of tumours with tumour stem cells have now been identified, including tumours derived from breast, brain, colon and prostate cancers, as well as leukaemias. Read full article

Asthma: Genetics

Asthma affects around 155 million individuals worldwide. Environmental factors contribute to disease progress, but genetic factors are also now being identified. Scientists are using this information to improve disease taxonomy and diagnosis. In this article, Saffron Willis-Owen describes the identification of genes contributing to asthma brought about by recent improvements using genotyping technology. She also considers the correlation between the development of asthma and simultaneous development of other atopic diseases such as eczema and allergic rhinitis. Read full article

Cell Suicide

Apoptosis is the process whereby a cell kills itself via a tightly, molecularly-regulated process. It therefore differs from necrosis, the process whereby a cell dies via lysis. Organisms use apoptosis as an essential tool to respond to cell insults such as viral infection or radiation, as well as to regulate tissue and organ development. Identifying the apoptotic process can be crucial for identifying early stages of disease. In this article, Glenda Globe and Brian Harmon examine ways to identify apoptosis correctly using different types of biochemical and morphological assays. Read full article

Investigating Bioterrorism

The danger of bioterrorism was exposed in 2001 when a number of biological attacks were conducted via the mail system in New York using spores from the bacterium Bacillus anthracis. The attacks resulted in a number of civilians being hospitalised. In an article on microbial forensics, Stephen Morse and Bruce Budowle address the processes that enable scientists to analyse and interpret evidence from the scene of an act of bioterrorism. Read full article

Brain Evolution

The central nervous system has changed over the course of time independently in different lineages of animals. The broad array of variation in nervous system structure reflects the diversity of successful niches and lifestyles available in the biological world. In this article, Ann Butler describes how parts of the central nervous system have elaborated. She demonstrates that evolution has not occurred in a simple, unilinear progressive manner and describes how this has resulted in a diversity of morphology such that both simpler and more complex nervous systems may be adaptive, depending on selective pressures. Read full article

Plant Peroxisomes and Glyoxysomes

Peroxisomes and glyoxysomes are membrane enclosures containing enzymes that participate in photorespiration in leaves, nitrogen metabolism in root nodules and fat conversions in seeds. Oxidases in these organelles circumvent energy conservation by producing hydrogen peroxide, which is detoxified by catalase in the matrix and ascorbate peroxidase in the membrane. In this article, Robert Donalson, Yoon Kwak, Tulin Yanik and Vishakha Sharma describe how recent genomic and proteomic analyses have revealed that plant peroxisomes and glyoxysomes can contain over a 100 different protein molecules, many still having unknown functions. Read full article

Post-fertilization Reproductive Strategies

Animals have diverse strategies that improve the success of their offspring after mating (i.e. post-fertilization reproductive strategies); the most common ones are parental care and offspring provisioning. The type, mode and duration of parental care exhibited by males and females depend on social and nonsocial environment, and on genetic and phylogenetic constraints. In this article, Rene van Dijk and Tamas Szekely overview five rapidly developing areas of parental care research, and conclude that sexual conflict between parents, social interactions and environmental conditions play important roles in determining post-fertilization reproductive strategies. Read full article

Bacteriophage: Therapeutic Uses

Bacteriophages are viruses that grow within bacteria, often killing the bacterial host in order to release the next generation of bacteriophages. Since their discovery in 1915, they have been identified as having potential for the control of bacterial disease. Following the widespread appearance of resistance to conventional antibiotics,  David Harper and Elizabeth Kutter describe how interest in this area has revived with clinical trials of bacteriophage therapeutics now under way. Read full article