Prolongation of clotting time in the dormant bat (Myotis lucifugus)

Résumé En été, la durée de coagulation du sang augmente notablement si l'on soumet la chauve-souris à une basse température (5°C); elle diminue dès qu'on replace l'animal dans un milieu chaud (23°C). Ceci indique l'existence d'un mécanisme adaptif qui prévient la formation du thrombus.     

Efficient delivery of siRNA for inhibition of gene expression in postnatal mice

It has recently been shown that RNA interference can be induced in cultured mammalian cells by delivery of short interfering RNAs (siRNAs). Here we describe a method for efficient in vivo delivery of siRNAs to organs of postnatal mice and demonstrate effective and specific inhibition of transgene expression in a variety of organs.     

A giant stream of metal-rich stars in the halo of the galaxy M31.

Recent observations have revealed streams of gas and stars in the halo of the Milky Way that are the debris from interactions between our Galaxy and some of its dwarf companion galaxies; the Sagittarius dwarf galaxy and the Magellanic clouds. Analysis of the material has shown that much of the halo is made up of cannibalized satellite galaxies, and that dark matter is distributed nearly spherically in the Milky Way. It remains unclear, however, whether cannibalized substructures are as common in the haloes of galaxies as predicted by galaxy-formation theory. Here we report the discovery of a giant stream of metal-rich stars within the halo of the nearest large galaxy, M31 (the Andromeda galaxy). The source of this stream could be the dwarf galaxies M32 and NGC205, which are close companions of M31 and which may have lost a substantial number of stars owing to tidal interactions. The results demonstrate that the epoch of galaxy building still continues, albeit at a modest rate, and that tidal streams may be a generic feature of galaxy haloes.     

Status of Descurainia torulosa (Brassicaceae)

Descurainia torulosa was established in 1983 based on material collected in northwestern Wyoming. The species is now known from 2 disjunct populations in southwestern Wyoming, and recent collections have expanded the known distribution within the northern portion of its range. The north-south disjunct distribution and apparent habitat differences have stimulated questions concerning the degree of relatedness between the disjunct elements to the point that the southern populations have been suggested to be a distinct taxon. Recognition of D. torulosa as a distinct species has also been questioned. This paper is based on field examination of D. torulosa populations, study of all known D. torulosa herbarium specimens, and analysis of nucleotide sequence from the internal transcribed spacer regions 1 and 2 of nuclear ribosomal DNA (ITS-1 & 2) from population exemplars. Cladistic analysis of the sequence data support our conclusion, based on morphological analysis. Northern and southern populations of D. torulosa are conspecific. Western North American Descurainia is in need of modern, critical taxonomic revision.     

A complementary DNA clone for a macrophage-lymphocyte Fc receptor

Macrophages, granulocytes and many lymphocytes express or secrete receptors for the Fc domain of immunoglobulins (Ig). These Fc receptors (FcRs) are heterogeneous and can be distinguished on the basis of their cellular distribution and specificities for different immunoglobulin isotypes. Although their functions are not completely understood, FcRs are known to be involved in triggering various effector cell functions and in regulating differentiation and development of B-cells. One of the best characterized is the mouse macrophage-lymphocyte receptor for IgG1 and IgG2b (ref. 5). On macrophages, this FcR mediates the endocytosis of antibody-antigen complexes via coated pits and coated vesicles, the phagocytosis of Ig-coated particles, and the release of various inflammatory and cytotoxic agents. It is possible that the receptor possesses an intrinsic ligand-activated ion channel activity responsible for some of these functions. The IgG1/IgG2b FcR has been isolated and shown to be a transmembrane glycoprotein of relative molecular mass (Mr) 47,000-60,000 (47-60 K) containing four N-linked oligosaccharide chains and a large (greater than 10K) cytoplasmic domain. It is also immunologically indistinguishable from the murine Ly-17 alloantigen which, in turn, is tightly linked to the Mls lymphocyte activation locus. Here we describe the isolation and characterisation of a complementary DNA clone encoding the whole of the IgG1/IgG2b FcR expressed by the mouse macrophage-like cell line P388D1. The receptor is a member of the immunoglobulin superfamily and, like Ly-17, maps to the distal portion of chromosome 1. cDNA probes detect one or two mRNA species in FcR+ macrophage and B-cell lines, but not in FcR- cells or a receptor-deficient variant derived from a FcR+ B-cell line. Finally, DNA hybridization analysis indicates the receptor gene is partially deleted or rearranged in the FcR- variant.     

Actin cables and epidermal movement in embryonic wound healing.

Skin wounds in embryos heal rapidly and perfectly. Even though the epidermis appears to be stretched taut over the surface of a structure such as a growing limb bud, its response to wounding is to close over the lesion, rather than to gape more widely. In adult wounds, the epidermis seems to migrate by means of lamellipodia, crawling over the exposed connective tissue. But in embryonic wounds we do not see lamellipodia. The epidermis at the edge of the wound looks smooth, as though under a circumferential tension. Here we show that a cable of filamentous actin appears to run continuously around most of the wound margin. It is confined to the single row of basal cells at the free edge of the epidermis. We suggest that the actin cable acts as a contractile 'purse string' to close up the embryonic wound.