Gene regulation during dedifferentiation in Dictyostelium discoideum

During development of Dictyostelium discoideum, cells acquire the capacity to rapidly recapitulate morphogenesis. Therefore, when cells at the loose aggregate stage are disaggregated and challenged to reaggregate, they do so in a tenth of the original time. If loose aggregate cells are disaggregated and resuspended in buffered dextrose solution (erasure medium), they retain the capacity of rapid recapitulation for 80 min, then completely lose this capacity in a single, synchronous step referred to as the "erasure event." The erasure event sets in motion a program of dedifferentiation during which cells lose developmentally acquired characteristics at different times. The erasure event is inhibited by the addition of 10(-4) M cAMP to erasure medium. The synthesis of 33 growth-associated polypeptides, the synthesis of 53 development-associated polypeptides, and the level of 2 development-associated RNAs have been monitored during the erasure program and in cultures inhibited from erasing by the addition of 10(-4) M cAMP. Growth-associated polypeptides begin to be resynthesized and development-associated polypeptides exhibit dramatic decreases in rate of synthesis at different times throughout the first 240 min in erasure medium. Inhibiting the erasure event with cAMP has no major effect in the resynthesis of the majority of growth-associated polypeptides. Only one growth-associated polypeptide, V28, is completely inhibited by cAMP, suggesting that it may play a role in the erasure process. In contrast, inhibiting the erasure event with cAMP has a marked effect on the synthesis of development-associated polypeptides, causing a dramatic reduction in the rate at which synthesis decreases for 6 polypeptides, and completely inhibits the decrease in the synthetic rate of 8 polypeptides. The two development-associated RNAs, 16G1 and 10C3, exhibit two distinctly different patterns of loss during erasure, but in both cases cAMP added at time zero of the erasure process dramatically retards or inhibits loss. In addition, when cAMP is added just prior to the erasure event, it inhibits the erasure event and stimulates a rapid increase in the level of 16G1 RNA back to the developmental level. The level of 16G1 RNA then remains at this level for at least 400 min. When cAMP is added after the erasure event, it causes a low, transient increase in the level of 16G1 RNA. These results are considered both in relation to the program of erasure, and in relation to the role of cAMP in the expression of developmental genes during the forward program of development.     

Characterization of binding of human fibrinogen to the surface of germ-tubes and mycelium of candida albicans

The binding of human fibrinogen to germ-tubes and mycelium of Candida albicans, forms usually found in infected tissues, was studied in vitro by an immunofluorescence assay. Binding was quantified by using 125I-labelled fibrinogen. The degree of binding differed according to the morphological form of the fungus. Binding relative to that of the yeast form was greater for mycelium (12-fold) than for germ-tube (7.7-fold). Pretreatment of yeasts with fragments D and E (terminal degradation products of fibrinogen) before fibrinogen binding showed that fragment D possessed a higher affinity for C. albicans than fragment E. Binding of fibrinogen was diminished when C. albicans was pretreated with 2-mercaptoethanol alone or in combination with pronase, or pretreated with alpha-mannosidase or trypsin. Binding was not decreased by pretreatment with pronase alone or chitinase. Inhibition experiments using C. albicans dialysed culture filtrate, C. albicans mannan, chitin, sugars or amino sugars were done by preabsorbing the fibrinogen with each of the above mentioned compounds. C. albicans dialysed culture filtrate inhibited the binding more strongly than C. albicans mannan. However, fibrinogen binding to C. albicans was not significantly reduced by mannose, several other sugars or chitin. These studies demonstrate the existence of a fibrinogen-binding factor (FBF) strongly associated with the surface of germ-tube and filamentous forms of C. albicans, and indicate a possible role for FBF in the pathogenicity of C. albicans.     

Evolution of four human Y chromosomal unique sequences

Four cloned unique sequences from the human Y chromosome, two of which are found only on the Y chromosome and two of which are on both the X and Y chromosomes, were hybridized to restriction enzyme-treated DNA samples of a male and a female chimpanzee (Pan troglodytes), gorilla (Gorilla gorilla), and pig-tailed macaque (Macaca nemestrina); and a male orangutan (Pongo pygmaeus) and gibbon (Hylobates lar). One of the human Y-specific probes hybridized only to male DNA among the humans and great apes, and thus its Y linkage and sequence similarities are conserved. The other human Y-specific clone hybridized to male and female DNA from the humans, great apes, and gibbon, indicating its presence on the X chromosome or autosomes. Two human sequences present on both the X and Y chromosomes also demonstrated conservation as indicated by hybridization to genomic DNAs of distantly related species and by partial conservation of restriction enzyme sites. Although conservation of Y linkage can only be demonstrated for one of these four sequences, these results suggest that Y-chromosomal unique sequence genes do not diverge markedly more rapidly than unique sequences located on other chromosomes. However, this sequence conservation may in part be due to evolution while part of other chromosomes.     

Life history adaptations of Gasterosteus aculeatus in a Mediterranean wetland

Synopsis The life cycle of leiurus-type Gasterosteus aculeatus occurring in a Mediterranean coastal wetland is described. Fish have a low number of lateral plates, short spines and marked sexual dimorphism in size. The life cycle is strictly annual, adults dying shortly after breeding. Adult fish migrate into seasonally-flooded freshwater marshes to breed, and the young migrate back to brackish water to pass the summer and autumn. Breeding occurs in March at water temperatures of about 10°C, the season lasting about 50 days. Growth of fish occurs throughout the year, but differs from year to year, resulting in variable adult size. Maximum gonadal investment of male fish is in autumn, whereas that of females is in spring. Gonadal investment of female fish, as measured by gonado-somatic index and fecundity, is higher than in other studied leiurus populations, but the number of clutches produced in a season is probably low. These differences in life history from other studied populations of sticklebacks are seen as adaptations to a mediterranean-type climate (high summer temperatures, seasonality of water bodies) and to heavy predation by fish-eating birds.     

Use of latex balls labelled by lectins in the demonstration of Salmonella-Schistosoma mansoni receptor sites

Surface tegumental membrane of adult stage Schistosoma mansoni were examined using the latex sphere coated with Concanavalin A (Con A). Wheat germ agglutinin (WGA) and Protein A (PA). Competitive saccharide inhibitors glucose, mannose and methyl alpha-D-glucopyranoside were used for Con A.     

β-Adrenergic receptor-coupled adenylate cyclase

Beta-adrenergic receptor-coupled adenylate cyclase is regulated by both amplification and desensitization processes. Desensitization of adenylate cyclase is divided into two major categories. Homologous desensitization is initiated by phosphorylation of the receptors by a beta-adrenergic receptor kinase. This reaction serves to functionally uncouple the receptors and trigger their sequestration away from the cell surface. These sequestered receptors can rapidly recycle to the cell surface or, with time, become down regulated, being destroyed within the cell. Dephosphorylation of the receptors is accomplished in the sequestered compartment of the cell, which may functionally regenerate the receptors and allow their return to the cell surface. In heterologous desensitization, receptor function is also regulated by phosphorylation, but in the absence of receptor sequestration or down regulation. In this case, phosphorylation serves only to functionally uncouple the receptors, that is, to impair their interactions with the guanine nucleotide regulatory protein Ns. Several protein kinases are capable of promoting this phosphorylation, including the cAMP-dependent kinase and protein kinase C. In addition to the receptor phosphorylation, heterologous desensitization is associated with modifications at the level of the nucleotide regulatory protein Ns and perhaps Ni. Adenylate cyclase systems are also subject to amplification that involves a protein kinase C-mediated phosphorylation of the catalytic unit of the enzyme. Phosphorylation of the catalytic unit enhances its catalytic activity and results in amplified stimulation by the regulatory protein Ns. Other receptor/effector systems exhibit qualitatively similar regulatory phenomena, suggesting that covalent modification (phosphorylation) may represent a general mechanism for regulating receptor function.     

The cell wall-plasmalemma interface in sieve tubes of barley

Both thick- and thin-walled sieve tubes in leaf-blade veins of Hordeum vulgare L. exhibit a distinct, electron-opaque inner wall layer after fixation in glutaraldehyde-osmium tetroxide and staining with uranyl acetate and lead citrate. This inner wall layer is thickest at the sieve plates and lateral sieve areas where it is permeated by a labyrinth of tubules formed by the plasmalemma. Along the lateral walls between sieve areas the inner wall layer apparently is penetrated by numerous microvilli-like evaginations of the plasmalemma, giving the cell wall-plasmalemma interface the appearance of a brush border. It is suggested that a similar brush-border-like structure may occur at the cell wall-plasmalemma interface of sieve elements in a wide variety of vascular plants.Abbreviation ER endoplasmic reticulum     

Mucosal epithelial cells and Langerhans cells are targets for infection by the immunosuppressive type D retrovirus simian AIDS retrovirus serotype 1

Simian acquired immune deficiency syndrome (SAIDS) caused by the type D retrovirus SRV-1 results in opportunistic infections and a spectrum of oral lesions similar to those seen in humans with AIDS. To better understand the pathogenesis of these oral lesions we have retrospectively examined the oral mucosa from ten rhesus monkeys that died with SAIDS and prospectively examined the oral mucosa of ten additional animals inoculated with SRV-1 to determine at what time, and in what cells SRV-1 infection of the oral mucosa occurs. Using single and double label immunohistologic techniques, and electron microscopy we detected SRV-1 in clusters of oral epithelial cells and rare Langerhans cells as early as 1 month postinoculation.     

Mapping of antibody specificities to V H gene families

V _H gene segments represent the products of the repeated duplication and subsequent diversification of a primordial V gene element. It is widely assumed that natural selection, operating via pathogens, has played the dominant role in this process. Here, we screen some 3.7 × 10⁴ C ⁺ colonies of mitogen-activated B cells for the production of antibodies specific for phosphorylcholine or hen egg lysozyme and expression of the V _H X-24, S107, Q52, or J558 gene families. These gene families were expressed at frequencies proportional to their genomic complexity among both unselected and antigen-specific C ⁺ colonies. Thus, the capacity to encode equivalent antibody-combining sites is dispersed uniformly among V _Hfamilies. This result suggests that individual V _H genes have not evolved to address specific antigens.