Similarity of the Structure of DNA from a Variety of Sources

DNA's from diverse cells of different species and from diverse tissues give the same x-ray diffraction pattern. The presently observable structure of DNA appears, then, to be the same in all cells. Thus, DNA in the resting state—the stored genetic material, from sperm of Paracentrotus lividus, Arbacia lixula, and salmon and from T₂ and T₇ bacteriophage—gives a pattern indistinguishable from DNA from very rapidly dividing cells, e.g., human acute leukemic leukocytes, human leukemic myeloid cells, mouse sarcoma 180, and bacteria—E. coli and pneumococci—during their logarithmic growth. The same x-ray patterns are given by DNA's from more slowly dividing tissues, e.g. calf liver, calf thymus, and human normal and leukemic lymphatic tissue. DNA from chicken erythrocytes—a DNA presumably metabolically inert—gives a similar picture. DNA's from several sources with a wide range in nitrogen base ratios, prepared independently by different workers using various methods, have given final products in varying yield; these all gave the same x-ray pattern, suggesting that all DNA is in the double-helical configuration. Finally, separation of the DNA molecule into a number of fractions with a varying adenine + thymine:guanine + cytosine ratio, but a constant adenine:thymine and guanine:cytosine ratio, each giving the same x-ray pattern as the original whole molecule, suggests that DNA cannot exist in significant amounts in forms other than the double-helix. X-ray diffraction photographs of sperm heads, extracted nucleoprotamine, calf thymus nuclei and extracted nucleohistone, and of chicken erythrocyte nuclei, are not all as well defined as those given by extracted DNA, but it is clear from the general characteristics of the pattern that much of the DNA bound to protein in these nuclei has the usual helical configuration, and that the double-helical structure of DNA exists in the cell and is not an artifact.     

Experimental manipulation reveals a trade‐off between weapons and testes

Theory predicts a trade‐off between sexually selected weapons used to secure mates and post‐copulatory traits used to maximize fertilization success. However, individuals that have a greater capacity to acquire resources from the environment may invest more in both pre‐ and post‐copulatory traits, and trade‐offs may not be readily apparent. Here, we manipulate the phenotype of developing individuals to examine allocation trade‐offs between weapons and testes in Mictis profana (Hemiptera: Coreidae), a species where the hind legs are sexually selected weapons used in contests over access to females. We experimentally prevented males from developing weapons by inducing them to autotomize their hind legs before the final moult to adulthood. We compared trait expression in this group to males where autotomy was induced in the mid‐legs, which are presumably not under sexual selection to the same extent. We found males without weapons invested proportionally more in testes mass than those with their mid‐legs removed. Males that developed to adulthood without weapons did not differ from the mid‐leg removal group in other traits potentially under precopulatory sexual selection, other post‐copulatory traits or naturally selected traits. In addition, a sample of adult males from the same population in the wild revealed a positive correlation between investment in testes and weapons. Our study presents a critical contribution to a growing body of literature suggesting the allocation of resources to pre‐ and post‐copulatory sexual traits is influenced by a resource allocation trade‐off and that this trade‐off may only be revealed with experimental manipulation.     

Arginine-glycine-aspartic acid-specific binding by foot-and-mouth disease viruses to the purified integrin alpha(v)beta3 in vitro.

The integrin alpha(v)beta3 has been shown to act as the receptor for internalization of foot-and-mouth disease virus (FMDV) (A12), with attachment being through a highly conserved RGD motif located on the G-H loop of viral capsid protein VP1. In addition, however, we have recently shown that efficient infection of culture-grown cells by FMDV (O1BFS) requires binding to cell surface heparan sulfate. In this study, we have used a solid-phase receptor binding assay to characterize the binding by FMDV to purified alpha(v)beta3 in the absence of heparan sulfate and other cell surface components. In this assay, FMDV (O1BFS) successfully replicated authentic ligand binding by cellular alpha(v)beta3 in terms of its high affinity, dependence on divalent cations, and activation by manganese ions. Virus binding to this preparation of alpha(v)beta3 was exquisitely sensitive to competition by short RGD-containing peptides (50% inhibition at < 10(-8) M peptide), and this inhibition was highly sequence specific, with the equivalent RGE peptide being at least 10(4) fold less effective as a competitor. Representative viruses of the other six serotypes of FMDV bound to alpha(v)beta3 in a similar RGD-specific manner, although significant differences in sensitivity to RGD peptides suggest that the affinity of the different FMDV serotypes for alpha(v)beta3 is influenced, in part, by the variable amino acid residues in the VP1 G-H loop on either side of the RGD.     

EFFECT OF LIGHT CYCLE ON DIATOM FATTY ACID COMPOSITION AND QUANTITATIVE MORPHOLOGY1

Quantitative cytological and fatty acid composition was determined for the diatom Cyclotella meneghiniana Kütz, Data from four separate experiments were examined to elucidate changes that may occur with respect to daily photoperiod. Overall, fatty acid composition is similar to that reported for other diatoms with the exception that the C16 fatty acids constitute approximately 70% of all fatty acids. The major fatty acids are C14:0, 16:1, 16:0, 18:0, and 20:5. Fatty acids that are present in minor amounts are iso-14:0, iso-15:0, 15:0, 17:0, 18:4, 18:2, 18:1, 19:0, 20:0, 22:0, and 23:0. Cytological composition is similar to that previously reported with the chloroplast and vacuole being the largest compartments within the cell. Changes in both cytological and fatty acid composition were studied with respect to the light / dark cycle. Chloroplast and lipid relative volume are greatest during the early part of the dark period. Nuclear relative volume is lowest in the dark and increases throughout the light period. Total unsaturated fatty acids, including the C20:5 fatty acid, are lowest in the early part of the light period and highest in the dark. The sum of the C16 fatty acids remains constant at 70% of total fatty acids in the cells throughout the light/dark cycle, although percent composition of these two fatty acids shifts. The data suggest that cyclical changes occur in both quantitative morphology and fatty acids composition with respect to daily photoperiod. The cells, although not rigidly synchronized, most likely divide in the latter part of the dark period or in the first hours of the light period. Lipids increase dramatically in the dark. The ecological implications of lipid storage are discussed in relation to lipophilic toxicants.     

Fluorinated Analogs of the Carotenoprotein, α-Crustacyanin

Four analogs of the carotenoprotein α-crustacyanin have been prepared by reconstitution with the all-transisomer of four new carotenoids (10-F, 10,10′-F₂and 14-F-astaxanthins, and 10′-F-adonirubin). All four blue carotenoproteins exhibit absorption spectra similar to that of the natural α-crustacyanin with λ_maxin the range of 613–625 nm. Different rates of pigment formation and yields were noted. F NMR spectra of pigments derived from the three 10F carotenoids have been recorded. Fourcisisomers of 14-F-astaxanthin and one of 10′-F-adonirubin were also isolated.     

Cell adhesion: more than just glue (review)

The ability of cells to interact with each other and their surroundings in a co-ordinated manner depends on multiple adhesive interactions between neighbouring cells and their extracellular environment. These adhesive interactions are mediated by a family of cell surface proteins, termed cell adhesion molecules. Fortunately these adhesion molecules fall into distinct families with adhesive interactions varying in strength from strong binding involved in the maintenance of tissue architecture to more transient, less avid, dynamic interactions observed in leukocyte biology. Adhesion molecules are extremely versatile cell surface receptors which not only stick cells together but provide biochemical and physical signals that regulate a range of diverse functions, such as cell proliferation, gene expression, differentiation, apoptosis and migration. In addition, like many other cell surface molecules, they have been usurped as portals of entry for pathogens, including prions. How the mechanical and chemical messages generated from adhesion molecules are integrated with other signalling pathways (such as receptor tyrosine kinases and phosphatases) and the role that aberrant cell adhesion plays in developmental defects and disease pathology are currently very active areas of research. This review focuses on the biochemical features that define whether a cell surface molecule can act as an adhesion molecule, and discusses five specific examples of how cell adhesion molecules function as more than just 'sticky' receptors. The discussion is confined to the signalling events mediated by members of the integrin, cadherin and immunoglobulin gene superfamilies. It is suggested that, by controlling the membrane organization of signalling receptors, by imposing spatial organization, and by regulating the local concentration of cytosolic adapter proteins, intercellular and cell-matrix adhesion is more than just glue holding cells together. Rather dynamic 'conversations' and the formation of multi-protein complexes between adhesion molecules, growth factor receptors and matrix macromolecules can now provide a molecular explanation for the long-observed but poorly understood requirement for a number of seemingly distinct cell surface molecules to be engaged for efficient cell function to occur.     

Consequences of sperm displacement for female dung flies,Scatophaga stercoraria

Displacement of stored sperm during copulation occurs in many insects. This process provides direct benefits for males via increased fertilization success, but the fitness consequences of sperm displacement for females are less clear. Here we investigate potential benefits of sperm displacement for female yellow dung flies, Scatophaga stercoraria. We find no evidence that female dung flies gain direct benefits from displacement of previously stored sperm in terms of increased fertility or fecundity. There was no difference in the relative survival rate, development time, size or fluctuating asymmetry of offspring produced by females that had previously stored sperm displaced before oviposition and those that did not. Females using previously stored sperm to fertilize their eggs produced significantly higher ratios of male to female offspring. These novel findings have important implications for understanding the evolutionary dynamics of male–female interactions in sperm competition.     

Polymorphism and divergence at the prune locus in Drosophila melanogaster and D. simulans

The prune locus of Drosophila melanogaster lies at the tip of the X chromosome, in a region of reduced recombination in which nearby loci show reduced variation relative to evolutionary divergence from D. simulans. DNA sequencing of prune alleles from D. melanogaster and D. simulans reveals extremely low variation in D. melanogaster but greater variation in D. simulans. Divergence between the two species is not reduced. This pattern may be explained by either positive selection leading to hitchhiking of neutral variation or background selection against deleterious mutations. The pattern of silent versus replacement polymorphism and divergence at prune is consistent with either a model of weakly deleterious selection against amino acid substitutions or balancing selection.