Hybridation ADN-ADN chez quelques espèces du genre Hansenula

The genus Hansenula was considered a long time ago as a good pattern for phylogenetic research. In 1969, Wickerham proposed an evolutive scheme based upon morphological, physiological and ecological criteria. Recently, relatedness among yeasts were analysed by DNA-DNA hybridization in liquid medium. H. anomala var. anomala (G + C content: 37,1%) was compared with H. anomala var. schneggii (37.6%), H. subpelliculosa (33,8%), H. ciferrii (33,1%), H. holstii (37%) belonging to the same line 2, and also with H. beckii (38,3%) line 3, H. sydowiorum (40,1%) and H. muscicola (37,1%).These results showed little relatedness between H. anomala var. anomala /H. ciferrii and H. anomala var. anomala/ H. subpelliculosa. On the other hand, H. anomala var. schneggii shared 89,5% of its nucleotide sequences with H. anomala var. anomala. These 2 strains were considered to represent the same species. H. holstii showed 67.1% complementarity with H. anomala var. anomala: this strain is considered to represent valid species, different from H. anomala var. anomala, but H. muscicola with 72.5% relatedness to H. anomala var. anomala could be considered as a limit species. An unexpected finding was that H. beckii was closely related to H. anomala var. anomala (84.8%). These data suggested the inadequacy of current criteria used to establish the phylogenetic lines in genus Hansenula.     

Polyomavirus growth and persistence in Friend erythroleukemic cells

Infection of Friend erythroleukemic (FL) cells by polyomavirus (Py) invariably results in the selection of persistently infected FL-Py cell lines and clones. Anti-Py serum treatment of FL-Py lines and clones leads to the loss of Py genome and consequent cell cure. Conversely, cure has not been obtained in FL-PytsA cell lines (isolated after infection by a Py thermosensitive early mutant) and their derivative clones cultivated for a long time at nonpermissive temperature (39 degrees C), where viral large-T protein is inactive. Rescue of viral particles has always been obtained after shifting cells to 32 degrees C. Integrated viral genomes were detected by blot hybridization in an FL-PytsA clone at 39 degrees C. Long-term observation of FL-Py cell lines and their derivative clones reveals a reciprocal selection mechanism (coevolution) between the viral and the cellular populations, resulting in either a completely virus-free Py-resistant FL cell line (cure) or in a continuously Py-shedding line bearing Py genome variants. Structural analysis of these viral populations has been carried out, and some viral variants have been isolated and characterized. On the basis of the results obtained, the possible mechanisms of Py persistence in FL cells will be discussed.     

Computer-based 3-dimensional reconstruction of major organ systems of a new aeolid nudibranch subspecies, Flabellina engeli lucianae, from Brazil (Gastropoda: Opisthobranchia)

Obtaining accurate and comprehensive anatomical informationfrom small opisthobranch specimens has been a major problem.Computer-based 3-dimensional reconstruction from serial histologicalslides applying AMIRA (TGS Graphics) software is shown to bean efficient and fully reproducible way to analyse tiny andcomplex organ systems in their true relative positions and proportions;this method is herein applied to nudibranchs for the first time.We used Flabellina engeli lucianae n. subsp., a small aeolid(up to 8 mm body preserved length) from subtropical southernBrazil, to illustrate all major organ systems including nervoussystems, and discuss them comparatively. Flabellina engeli lucianaediffers externally from congeners by having a translucent bodywith opaque white and iridescent blue spots, orange ceratalbands, and by the special branching of cerata forming distinctgroups on common peduncles. External and internal differencesfrom the apparently geographically and hydrographically separatedCaribbean specimens of F. engeli engeli Marcus & Marcus,1968 are discussed in detail. (Received 9 January 2006; accepted 10 July 2007)     

The other Janus face of Qa-1 and HLA-E: diverse peptide repertoires in times of stress

The non-polymorphic MHC molecule Qa-1 and its human counterpart HLA-E present monomorphic signal peptides to innate receptors and thereby regulate lymphocyte activity. Under stress, this peptide content is replaced with a surprisingly diverse repertoire of novel peptides that are associated with heat-shock proteins, infectious agents or antigen processing defects.     

Micromere-specific cell surface proteins of 16-cell stage sea urchin embryos

Evidence is presented of cell-type specificity of surface proteins from the 16-cell stage sea urchin embryo. The protein composition of the micromere cell surface has been examined by 125I labelling of intact cells followed by SDS-PAGE. In Arbacia punctulata, four high molecular weight (HMW) proteins are detected on the surface of isolated micromeres--but not on mesomere-macromere fractions. In Strongylocentrotus droebachiensis, a micromere-specific protein of 133 K molecular weight (MW) was identified. This 133 K protein binds to wheat germ agglutinin (WGA) but not to concanavalin A (conA). Lectin binding was studied using a new technique. The procedure involves the separation, by SDS-PAGE, of iodinated cell-surface proteins followed by their electrophoretic transfer to lectin-coated nitrocellulose membranes. Using this procedure, cell-type-specific surface proteins which are also lectin-binding-specific, were detected.     

Biomimesis and biomorphic transformations: New concepts applied to bone regeneration

In the last decades the activity of material scientists was more and more directed to the development of biomimetic scaffolds, able to drive and address cell activity towards proper differentiation and the repair of diseased human tissues. In case of bone, this requires the synthesis of three-dimensional constructs able to exchange chemical signals promoting osteogenesis and to progressively be resorbed during the formation and remodelling of new bone. Besides, particularly for the regeneration of extensive portions of bone, a morphological and mechanical biomimesis is also required, to allow cell colonization and formation of a proper vascularization tree. The healing of load-bearing bones also requires scaffolds with a hierarchically organized morphology, to provide improved biomechanical behaviour and allow a proper mechano-transduction of the mechanical stimuli down to the cell level. The present paper is an overview of the current technologies and devices developed in the last decade for the regeneration of bone tissue. In particular, novel biomimetic and biomorphic scaffolds, obtained by the controlled transformation of native ligneous structures, promise to adequately face the problem of obtaining complex hierarchical structures, not achievable otherwise by any currently existing manufacturing techniques.