Unstable genetic system inDrosophila melanogaster: I. Instability at theCinnabar locus

Summary A mutant strain containing acinnabar allele (cn ^rbr ,rojo brillante) is reported, that produces wild-type revertants at thecinnabar (cn) locus. Incn ^rbr /cn heterozygotes the rate of mutation is highly increased. The presence of a mutator agent acting premeiotically is indicated.D.L. Lindsley and E.H. Grell, Genetic variations ofDrosophila melanogaster. Carnegie Institution of Washington, Washington, 1968; Publication No. 627.     

Genetic and epigenetic incompatibilities underlie hybrid dysgenesis in Peromyscus

Crosses between the two North American rodent species Peromyscus polionotus (PO) and Peromyscus maniculatus (BW) yield parent-of-origin effects on both embryonic and placental growth. The two species are approximately the same size, but a female BW crossed with a male PO produces offspring that are smaller than either parent. In the reciprocal cross, the offspring are oversized and typically die before birth. Rare survivors are exclusively female, consistent with Haldane's rule, which states that in instances of hybrid sterility or inviability, the heterogametic sex tends to be more severely affected. To understand these sex- and parent-of-origin-specific patterns of overgrowth, we analysed reciprocal backcrosses. Our studies reveal that hybrid inviability is partially due to a maternally expressed X-linked PO locus and an imprinted paternally expressed autosomal BW locus. In addition, the hybrids display skewing of X-chromosome inactivation in favour of the expression of the BW X chromosome. The most severe overgrowth is accompanied by widespread relaxation of imprinting of mostly paternally expressed genes. Both genetic and epigenetic mechanisms underlie hybrid inviability in Peromyscus and hence have a role in the establishment and maintenance of reproductive isolation barriers in mammals.     

A novel metalloproteinase gene specifically expressed in stromal cells of breast carcinomas.

A gene has been identified that is expressed specifically in stromal cells surrounding invasive breast carcinomas. On the basis of its sequence, the product of this gene, named stromelysin-3, is a new member of the family of metalloproteinase enzymes which degrade the extracellular matrix. The suggestion is that stromelysin-3 is one of the stroma-derived factors that have long been postulated to play an important part in progression of epithelial malignancies.     

Trefoil factors

Trefoil Factor 1 (TFF1), the first member of the trefoil factor family, is normally expressed in the stomach mucosa. Ectopic expression is also observed in various human pathological conditions, notably in numerous carcinomas and gastrointestinal acute inflammatory disorders. In vivo experimental data using TFF1-deficient mice highlight the pleiotropic functions of TFF1: (i) it is a gastric tumor suppressor gene involved in gastric ontogenesis and homeostasis; (ii) it protects gut mucosa from aggression; (iii) it participates in folding secreted proteins inside the endoplasmic reticulum. At the cellular level, it limits cell proliferation and apoptosis, and favors cell differentiation. Collectively, these data suggest that TFF1 may provide an alternative pharmacological tool for the prevention and treatment of human gastrointestinal diseases.     

Radioautographic analysis of retinofugal projections in the primitive bony fish Polypterus senegalus C.]

Retinofugal pathways of Polypterus senegalus C. have been examined by means of the radioautographic method. Contralaterally the retina projects to the hypothalamus, thalamus, pretectum and tectum. An important ipsilateral component has been observed. No retinal projection to the mesencephalic tegmentum has been identified. Comparing the primary optic system of Polypterus with that of other body Fish, indicates that this species possesses a combination of characteristics which are both actinopterygian and sarcopterygian. The significance of this mozaic arrangement is discussed.     

The thermodynamic meaning of negative entropy

The heat generated by computations is not only an obstacle to circuit miniaturization but also a fundamental aspect of the relationship between information theory and thermodynamics. In principle, reversible operations may be performed at no energy cost; given that irreversible computations can always be decomposed into reversible operations followed by the erasure of data, the problem of calculating their energy cost is reduced to the study of erasure. Landauer's principle states that the erasure of data stored in a system has an inherent work cost and therefore dissipates heat. However, this consideration assumes that the information about the system to be erased is classical, and does not extend to the general case where an observer may have quantum information about the system to be erased, for instance by means of a quantum memory entangled with the system. Here we show that the standard formulation and implications of Landauer's principle are no longer valid in the presence of quantum information. Our main result is that the work cost of erasure is determined by the entropy of the system, conditioned on the quantum information an observer has about it. In other words, the more an observer knows about the system, the less it costs to erase it. This result gives a direct thermodynamic significance to conditional entropies, originally introduced in information theory. Furthermore, it provides new bounds on the heat generation of computations: because conditional entropies can become negative in the quantum case, an observer who is strongly correlated with a system may gain work while erasing it, thereby cooling the environment.     

Glycoprotein organization of Chikungunya virus particles revealed by X-ray crystallography

Chikungunya virus (CHIKV) is an emerging mosquito-borne alphavirus that has caused widespread outbreaks of debilitating human disease in the past five years. CHIKV invasion of susceptible cells is mediated by two viral glycoproteins, E1 and E2, which carry the main antigenic determinants and form an icosahedral shell at the virion surface. Glycoprotein E2, derived from furin cleavage of the p62 precursor into E3 and E2, is responsible for receptor binding, and E1 for membrane fusion. In the context of a concerted multidisciplinary effort to understand the biology of CHIKV, here we report the crystal structures of the precursor p62-E1 heterodimer and of the mature E3-E2-E1 glycoprotein complexes. The resulting atomic models allow the synthesis of a wealth of genetic, biochemical, immunological and electron microscopy data accumulated over the years on alphaviruses in general. This combination yields a detailed picture of the functional architecture of the 25?MDa alphavirus surface glycoprotein shell. Together with the accompanying report on the structure of the Sindbis virus E2-E1 heterodimer at acidic pH (ref. 3), this work also provides new insight into the acid-triggered conformational change on the virus particle and its inbuilt inhibition mechanism in the immature complex.     

Defining the core Arabidopsis thaliana root microbiome

Land plants associate with a root microbiota distinct from the complex microbial community present in surrounding soil. The microbiota colonizing the rhizosphere (immediately surrounding the root) and the endophytic compartment (within the root) contribute to plant growth, productivity, carbon sequestration and phytoremediation. Colonization of the root occurs despite a sophisticated plant immune system, suggesting finely tuned discrimination of mutualists and commensals from pathogens. Genetic principles governing the derivation of host-specific endophyte communities from soil communities are poorly understood. Here we report the pyrosequencing of the bacterial 16S ribosomal RNA gene of more than 600 Arabidopsis thaliana plants to test the hypotheses that the root rhizosphere and endophytic compartment microbiota of plants grown under controlled conditions in natural soils are sufficiently dependent on the host to remain consistent across different soil types and developmental stages, and sufficiently dependent on host genotype to vary between inbred Arabidopsis accessions. We describe different bacterial communities in two geochemically distinct bulk soils and in rhizosphere and endophytic compartments prepared from roots grown in these soils. The communities in each compartment are strongly influenced by soil type. Endophytic compartments from both soils feature overlapping, low-complexity communities that are markedly enriched in Actinobacteria and specific families from other phyla, notably Proteobacteria. Some bacteria vary quantitatively between plants of different developmental stage and genotype. Our rigorous definition of an endophytic compartment microbiome should facilitate controlled dissection of plant-microbe interactions derived from complex soil communities.