Multimeric arrays of the yeast retrotransposon Ty.

We have identified a novel integrated form of the yeast retrotransposon Ty consisting of multiple elements joined into large arrays. These arrays were first identified among Ty-induced alpha-pheromone-resistant mutants of MATa cells of Saccharomyces cerevisiae which contain Ty insertions at HML alpha that result in the expression of that normally silent cassette. These insertions are multimeric arrays of both the induced genetically marked Ty element and unmarked Ty elements. Structural analysis of the mutations indicated that the arrays include tandem direct repeats of Ty elements separated by only a single long terminal repeat. The Ty-HML junction fragments of one mutant were cloned and shown to contain a 5-base-pair duplication of the target sequence that is characteristic of a Ty transpositional insertion. In addition, the arrays include rearranged Ty elements that do not have normal long terminal repeat junctions. We have also identified multimeric Ty insertions at other chromosomal sites and as insertions that allow expression of a promoterless his3 gene on a plasmid. The results suggest that Ty transposition includes an intermediate that can undergo recombination to produce multimers.     

Concordance between Parental Origin of Chromosome 13q Loss and 6p Duplication in Sporadic Retinoblastoma

Two hypotheses are capable of explaining nonrandom loss of one parent's alleles at tumor suppressor loci in sporadic cases of several pediatric cancers, including retinoblastoma—namely, preferential germ-line mutation or chromosome imprinting. We have examined 74 cases of sporadic retinoblastoma for tumors in which at least two genetic events—loss of heterozygosity for chromosome 13q markers and formation of an isochromosome 6p—have occurred. Sixteen cases were found to contain both events. In 13 of 16 such tumors, the chromosomes 13q that were lost and chromosomes 6p that were duplicated are derived from the same parent. These data may be explained within the framework of the genome imprinting model but are not predicted by preferential germ-line mutation.     

Disruption of a Silencer Domain by a Retrotransposon

A galactose-inducible Ty element carrying the HIS3 gene has been used as an insertional mutagen to generate alpha-factor resistant mutants. This collection of Ty-induced mutations includes insertions into the gene for the alpha-factor receptor (STE2), several nonspecific STE genes, and mutations that lead to the expression of the normally silent HML alpha locus. The hml alpha "on" mutations fall into two classes, those that disrupt trans-acting regulators involved in silencing HML alpha and a novel class of mutations that activate HML alpha by insertion at that locus. The hml alpha::Ty "on" mutations illustrate the unusual ability of these retrotransposons to activate genes by overcoming gene silencing mechanisms. The hml alpha::Ty "on" mutations include examples of multimeric Ty arrays. Single Ty and solo delta insertion derivatives of these Ty multimers restore the ability of the silencing mechanism to repress HML alpha.     

Three viruses found in the braconid parasitoid Microplitis croceipes and their implications in biological control programs

Productivity and longevity decreased in a laboratory colony of the parasitoid wasp Microplitis croceipes (Cresson) (Hymenoptera: Braconidae). Using light microscopy, it was determined that the colony was free of microsporidia. However, samples of the colony examined for pathogens by electron microscopy revealed three types of viruses: a nonpathogenic polydnavirus which is produced by all female wasps; a nonoccluded baculovirus which is pathogenic to late-stage pupae and adults; and a picorna-like virus which is present in larvae, pupae, and adults. The nonoccluded baculovirus was eliminated from the laboratory colony of M. croceipes by selection of progeny from wasps which had oviposited within 2 to 3 days after emergence from the cocoons and which had lived for at least 14 days post-emergence. Upon death, the wasps were examined by negative stain electron microscopy and only progeny from baculovirus-free wasps were retained. Parasitoid colonies should be systematically examined for pathogenic viruses that may reduce their productivity and efficacy as biological control agents. In addition, exotic parasitoids and predators should be evaluated for viruses and other pathogens while in quarantine.     

A phase III comparison of methyl-CCNU + vincristine with or without BCG + allogeneic tumor cells in metastatic melanoma

Summary Sixty-two patients with metastatic malignant melanoma were randomized to treatment with either (a) methyl-CCNU (200 mg/m², PO every 8 weeks) plus vincristine (2 mg IV every 4 weeks), or (b) the same chemotherapy plus intradermal (ID) injections of irradiated (15,000 rads) allogeneic (fresh-frozen) melanoma cells (1–2×10⁸) admixed with BCG (Glaxo, 2–4.5×10⁶ organisms) every 2 weeks. Treatment cycles were repeated every 8 weeks until tumor progression. Seven (2 CR, 5 PR) objective remissions were noted among 31 patients (22.5%) treated with chemotherapy alone, whereas six (3 CR, 3 PR) objective remissions were noted among 31 patients (19%) treated with chemoimmunotherapy (P>0.05). The medians for remission duration (6 months) and survival (6.5 months) in the chemotherapy group did not differ significantly from the medians for remission duration (8 months) and survival (8 months) in the chemoimmunotherapy group. The patients manifested no unexpected toxicity. Hematologic toxicity was experienced by patients on both regimens; however, those receiving chemoimmunotherapy rebounded more quickly.     

Antagonism of membrane compression effects by high pressure gas mixtures in a phospholipid bilayer system

Binary mixtures of helium with nitrogen, xenon or nitrous oxide were applied to suspensions of phosphatidylcholine-cholesterol vesicles to determine those mixtures of lipid soluble gases which would exactly antagonize the membrane rigidifying effect of 100 ATA compression. A previous study has shown that the initial application of 100 ATA compression by gas produces a significant reduction in the fluidity of the phospholipid bilayer. However, as the high pressure gas dissolves into the lipid region it creates disorder and increases fluidity. Fluidity of the bilayer at equilibrium represents the sum of the compression-ordering and dissolved-gas disordering effects and is dependent on the gas/lipid partition coefficient of the particular gas. The beneficial effect of a narcotic gas added to Trimix mixtures to ameliorate HPNS in deep divers may be due to a balance of compression-ordering and solubility-disordering effects achieved within the nerve membrane. It is therefore valuable to determine those gas mixtures which achieve balance of these two effects and result in zero net change in phospholipid bilayer fluidity at an established pressure of 100 ATA. Binary mixtures of helium with 88% nitrogen, 3.8% xenon or 2.8% nitrous oxide resulted in zero net change in bilayer fluidity with our model system at 100 ATA. A graph of the percent of narcotic gas needed to produce zero net effect as a function of pressure, however, was nonlinear. This would suggest the ratio of gases in Trimix must be varied as a function of pressure. While the phosphatidylcholine-cholesterol bilayer is a good model for certain components of the nerve membrane, it does not allow for study of protein-lipid or gas-protein interactions. The data presented thus aid in our understanding of HPNS but are yet incomplete for precise use in predicting diving mixtures.     

What drives interspecies graft union success? Exploring the role of phylogenetic relatedness and stem anatomy

The underlying mechanisms that determine whether two species can form a successful graft union (graft compatibility) remain obscure. Two prominent hypotheses are (1) the more closely related species are, the higher the graft success and (2) the vascular anatomy at the graft junction influences graft success. In this paper these two hypotheses are examined in a systematic way using graft combinations selected from a range of (a) phylogenetically close and more distant legume species, (b) species displaying different germination patterns and (c) scions and rootstocks possessing contrasting stem tissues and vascular patterns. Relatedness of species was not a good predictor of graft compatibility, as vascular reconnection can occur between distantly related species and can fail to occur in some more closely related species. Similarly, neither the stem tissues present at the graft junction nor the vascular anatomy correlated with the success of vascular reconnection. Relatedness and stem anatomy therefore do not appear to be the determining factors in successful vascular reconnection after grafting in legumes. These results are discussed in conjunction with other hypotheses such as the role of auxin.     

Mechanisms of outer membrane vesicle entry into host cells

Bacterial outer membrane vesicles (OMVs) are nano‐sized compartments consisting of a lipid bilayer that encapsulates periplasm‐derived, luminal content. OMVs, which pinch off of Gram‐negative bacteria, are now recognized as a generalized secretion pathway which provides a means to transfer cargo to other bacterial cells as well as eukaryotic cells. Compared with other secretion systems, OMVs can transfer a chemically extremely diverse range of cargo, including small molecules, nucleic acids, proteins, and lipids to proximal cells. Although it is well recognized that OMVs can enter and release cargo inside host cells during infection, the mechanisms of host association and uptake are not well understood. This review highlights existing studies focusing on OMV‐host cell interactions and entry mechanisms, and how these entry routes affect cargo processing within the host. It further compares the wide range of methods currently used to dissect uptake mechanisms, and discusses potential sources of discrepancy regarding the mechanism of OMV uptake across different studies.     

Tumor-Stroma Mechanics Coordinate Amino Acid Availability to Sustain Tumor Growth and Malignancy

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