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1203. Chemical codes for the control of behaviour in arthropods.
Neuromodulators and hormones elicit and modify well-defined behaviours. Their mode of action can be studied to advantage in arthropods, where the natural releasing cells and neuronal target circuits are concisely identified. The coordinated actions of biogenic amines and peptides on both central and peripheral neural activity and metabolic processes bias the whole organism to perform a coherent behavioural routine.
1204. Deleterious mutations and the evolution of sexual reproduction.
The origin and maintenance of sexual reproduction continues to be an important problem in evolutionary biology. If the deleterious mutation rate per genome per generation is greater than 1, then the greater efficiency of selection against these mutations in sexual populations may be responsible for the evolution of sex and related phenomena. In modern human populations detrimental mutations with small individual effects are probably accumulating faster than they are being eliminated by selection.
1205. Trophic regulation of nerve cell morphology and innervation in the autonomic nervous system.
A remarkable feature of nerve cells is the complex and variable pattern of their axonal and dendritic branches. Quantitative studies of a simple part of the nervous system in mammals provide evidence that neuronal geometry and innervation are regulated by long-term trophic interactions between neurons and their targets. This trophic linkage may explain how nerve cells adjust their function to the needs of bodies that vary markedly in size and form.
1206. How eukaryotic transcriptional activators work.
A specific protein, bound to DNA, can activate transcription of a wide array of genes in many eukaryotes. Further analysis suggests a general outline for how eukaryotic transcriptional activators function and are controlled.
1207. The functional logic of cortical connections.
Patterns of anatomical connections in the visual cortex form the structural basis for segregating features of the visual image into separate cortical areas and for communication between these areas at all levels to produce a coherent percept. Such multi-stage integration may be a common strategy throughout the cortex for producing complex behaviour.
1208. The molecular genetics of embryonic pattern formation in Drosophila.
Analysis of the genes that control the early events of Drosophila embryogenesis is providing details of the molecular processes underlying the positional specification of cells. There are two distinct phases: the first precedes the cellularization of the blastoderm embryo and is associated with a cascade of interactions between transcriptional regulators; the second occurs after cellularization and depends on communication between cells. These processes may be conserved in a wide range of invertebrates and vertebrates.
1209. The molecular heterogeneity of protein kinase C and its implications for cellular regulation.
Protein kinase C is now known to be a large family of proteins, with multiple subspecies that have subtle individual enzymological characteristics. Some members of the family exhibit distinct patterns of tissue expression and intracellular localization; different kinases probably have distinct functions in the processing and modulation of a variety of physiological and pathological responses to external signals.
1210. T-cell antigen receptor genes and T-cell recognition.
The four distinct T-cell antigen receptor polypeptides (alpha, beta, gamma, delta) form two different heterodimers (alpha:beta and gamma:delta) that are very similar to immunoglobulins in primary sequence, gene organization and modes of rearrangement. Whereas antibodies have both soluble and membrane forms that can bind to antigens alone, T-cell receptors exist only on cell surfaces and recognize antigen fragments only when they are embedded in major histocompatibility complex (MHC) molecules. Patterns of diversity in T-cell receptor genes together with structural features of immunoglobulin and MHC molecules suggest a model for how this recognition might occur. This view of T-cell recognition has implications for how the receptors might be selected in the thymus and how they (and immunoglobulins) may have arisen during evolution.
1213. Mysteries of HIV: challenges for therapy and prevention.
A number of problems still surround infection by the human immunodeficiency virus and the pathogenesis of AIDS. Solutions to the problems would provide valuable information for the development of antiviral therapy and a vaccine.
1218. Quantitative assessment of worldwide contamination of air, water and soils by trace metals.
Calculated loading rates of trace metals into the three environmental compartments demonstrate that human activities now have major impacts on the global and regional cycles of most of the trace elements. There is significant contamination of freshwater resources and an accelerating accumulation of toxic metals in the human food chain.
1219. Roles of G protein subunits in transmembrane signalling.
A family of proteins called G proteins couples cell surface receptors to a variety of enzymes and ion channels. Since many cells contain several very similar G proteins, an important question is how signals remain specific as they cross the cell membrane.
1220. Two-tiered regulation of spatially patterned engrailed gene expression during Drosophila embryogenesis.
作者: S DiNardo.;E Sher.;J Heemskerk-Jongens.;J A Kassis.;P H O'Farrell.
来源: Nature. 1988年332卷6165期604-9页
A regulatory cascade, initiated during the syncytial stage of embryogenesis, culminates in the striped pattern of engrailed gene expression at the cellular blastoderm stage. The early regulatory genes, for example the pair-rule genes, are expressed transiently and as their products decay a distinct regulatory programme involving segment polarity genes takes over. This late programme maintains and perhaps modifies the striped pattern of engrailed expression through interactions that may involve cell communication.
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