Multivariate analyses of carbohydrate data from lipopolysaccharides of Actinobacillus (Haemophilus) actinomycetemcomitans, Haemophilus aphrophilus, and Haemophilus paraphrophilus

The taxonomic distinction between Actinobacillus (Haemophilus) actinomycetemcomitans and Haemophilus aphrophilus and the taxonomic distinction between H. aphrophilus and Haemophilus paraphrophilus have been questioned. This study was done to determine whether multivariate statistical analyses of carbohydrate data from lipopolysaccharides could be used to distinguish between these closely related species. Lipopolysaccharides were extracted with phenol-water and purified. Carbohydrates were assessed by using gas chromatography and gas chromatography-mass spectrometry after methanolysis and derivatization with trifluoroacetic acid anhydride. The lipopolysaccharides from all of the species contained rhamnose, fucose, galactose, glucose, L-glycero-D-mannoheptose, and glucosamine plus galactosamine, but in varying amounts. A. actinomycetemcomitans and H. paraphrophilus also contained D-glycero-D-mannoheptose, while H. aphrophilus did not. Sample- and variable-oriented principal-component analyses of the carbohydrate data clearly distinguished among A. actinomycetemcomitans, H. aphrophilus, and H. paraphrophilus. Soft independent modelling of class analogy showed that no sample in the A. actinomycetemcomitans class fell within the 95% confidence limits of the H. aphrophilus class. H. paraphrophilus fell outside both classes.     

Interaction of Ia-molecule of specific T-suppressor with complementary structure of syngeneic responding T-lymphocyte

To achieve inhibition of proliferation of alloantigen-induced T-lymphocytes in mixed lymphocyte culture by specific suppressor T cells (SSTC), identity of SSTC and responder in MHC class II antigens is required; either in IC or in IA + IE. By shielding of the SSTC with antiserum to ICd product (without complement), it is demonstrated that ICd product is expressed on the SSTC surface only, rather than on the surface of both stimulator and responder cells (native or preactivated with the alloantigen). Pretreatment of SSTC with anti-ICd antibodies in the absence of complement does not prevent specific SSTC interaction with the alloantigen, but prevents the SSTC function in reversible fashion. Because part of responders preactivated with an alloantigen acquired a capacity to adhere to the syngeneic SSTC monolayer, it is supposed that a receptor to the syngeneic Ia-molecule of SSTC membrane arises on the surface of preactivated responder T cells, which results in direct interaction between these two cells, reflecting the "interactional restriction" mechanism of SSTC function.     

Requirement for the location of both appropriate and irrelevant H-2 antigens on the same stimulator cell for unspecific DNA-synthesis inhibition by the H-2-antigen-primed,specific suppressor T cells

Specific suppressor T cells (SSTC), primed in vivo with H-2 antigens, have been shown previously to inhibit DNA synthesis in the one-way, three-cell mixed lymphocyte reaction (MLR) provided that (a) the stimulator cells bear the priming H-2 antigens, and (b) the responder cells possessIC+S regions homologous to those of the SSTC. Anti-B10.A BlO.A(2R) SSTC (anti-D^d) and anti-A.AL A.TL SSTC (anti-K^k) are shown here to be able to inhibit the DNA synthesis triggered in MLR, not only by the corresponding antigens, D^d and K^k, respectively, but also by irrelevant, third-party H-2 and Mls products provided that the corresponding and third-party antigens are presented on the same stimulator cell. If stimulatorH-2 regions, whose products interact with SSTC and responders, are located on different stimulator cells within the particular MLR, SSTC activity is not elicited. Participation of cytotoxic T lymphocytes in DNA-synthesis suppression is ruled out. Direct contact or location of the inhibited responder cell very close to SSTC is considered to be required for the development of SSTC activity.     

Interaction of anti-Kb and anti-Dd effector lymphocytes with target cells of mouse mutant haplotypes]

The magnitude of the cytotoxic effect (CE) of immune lymphocytes R101 anti-Kb (C57BL/6) and R101 anti-Dd (B10.D2) upon target cells (TC) of mutants Kba (Hzl) and Kbd (M505), as well as Dda (M504) was considerably less than that on the TC of the original C57BL/6 and B10.D2 strains, respectively. A decrease of the CE on the H (zl) and M504 TC was more prominent than that on the M505 TC. "Monospecific" lymphocytes anti-Kb and anti-Dd were separated into two distinct subpopulations by absorption on the monolayers of macrophages from the mutant strains of mice. One of the subpopulations reacted with the TC of the original strain only, whereas the other one - with the TC of both the original and mutant strains.     

Contrasted histories of organelle and nuclear genomes underlying physiological diversification in a grass species

C₄ photosynthesis evolved multiple times independently in angiosperms, but most origins are relatively old so that the early events linked to photosynthetic diversification are blurred. The grass Alloteropsis semialata is an exception, as this species encompasses C₄ and non-C₄ populations. Using phylogenomics and population genomics, we infer the history of dispersal and secondary gene flow before, during and after photosynthetic divergence in A. semialata. We further analyse the genome composition of individuals with varied ploidy levels to establish the origins of polyploids in this species. Detailed organelle phylogenies indicate limited seed dispersal within the mountainous region of origin and the emergence of a C₄ lineage after dispersal to warmer areas of lower elevation. Nuclear genome analyses highlight repeated secondary gene flow. In particular, the nuclear genome associated with the C₄ phenotype was swept into a distantly related maternal lineage probably via unidirectional pollen flow. Multiple intraspecific allopolyploidy events mediated additional secondary genetic exchanges between photosynthetic types. Overall, our results show that limited dispersal and isolation allowed lineage divergence, with photosynthetic innovation happening after migration to new environments, and pollen-mediated gene flow led to the rapid spread of the derived C₄ physiology away from its region of origin.     

Polyploidy does not control all: Lineage‐specific average chromosome length constrains genome size evolution in ferns

Recent studies investigating the evolution of genome size diversity in ferns have shown that they have a distinctive genome profile compared with other land plants. Ferns are typically characterized by possessing medium‐sized genomes, although a few lineages have evolved very large genomes. Ferns are different from other vascular plant lineages as they are the only group to show evidence for a correlation between genome size and chromosome number. In this study, we aim to explore whether the evolution of fern genome sizes is not only shaped by chromosome number changes arising from polyploidy but also by constraints on the average amount of DNA per chromosome. We selected the genus Asplenium L. as a model genus to study the question because of the unique combination of a highly conserved base chromosome number and a high frequency of polyploidy. New genome size data for Asplenium taxa were combined with existing data and analyzed within a phylogenetic framework. Genome size varied substantially between diploid species, resulting in overlapping genome sizes among diploid and tetraploid spleenworts. The observed additive pattern indicates the absence of genome downsizing following polyploidy. The genome size of diploids varied non‐randomly and we found evidence for clade‐specific trends towards larger or smaller genomes. The 578‐fold range of fern genome sizes have arisen not only from repeated cycles of polyploidy but also through clade‐specific constraints governing accumulation and/or elimination of DNA.     

Site-specific conformational studies of prion protein (PrP) amyloid fibrils revealed two cooperative folding domains within amyloid structure

Despite the ability of most proteins to form amyloid, very little is know about amyloid fibril structures and the factors that govern their stability. Using amyloid fibrils produced from full-length prion protein (PrP), we describe a reliable approach for determining both site-specific and global conformational stability of the fibrillar form. To measure site-specific stability, we produced six variants of PrP by replacing the residues at positions 88, 98, 127, 144, 196, and 230 with cysteine, labeled the new cysteines with the fluorescent dye acrylodan, and investigated their conformational status within the amyloid form in guanidine hydrochloride-induced denaturation experiments. We found that the fibrils labeled at positions 127, 144, 196, and 230 displayed cooperative unfolding and showed a very high C1/2 value similar to that observed for the global unfolding of the amyloid structure. The unfolding at residue 98 was also cooperative; however, it showed a C1/2 value substantially lower than that of global unfolding, whereas the unfolding of fibrils labeled at residue 88 was non-cooperative. These data illustrate that there are at least two independent cooperative folding domains within the amyloid structure of the full-length PrP. In addition, kinetic experiments revealed only a partial overlap between the region that constituted the fibrillar cross-beta core and the regions that were involved in nucleation. This result illustrates that separate PrP regions accounted for the nucleation and for the formation of the conformationally most stable fibrillar core.