Molecular adaptation of a leaf-eating bird: stomach lysozyme of the hoatzin

This report describes a lysozyme expressed at high levels in the stomach of the hoatzin, the only known foregut-fermenting bird. Evolutionary comparison places it among the calcium-binding lysozymes rather than among the conventional types. Conventional lysozymes were recruited as digestive enzymes twice in the evolution of mammalian foregut fermenters, and these independently recruited lysozymes share convergent structural changes attributed to selective pressures in the stomach. Biochemical convergence and parallel amino acid replacements are observed in the hoatzin stomach lysozyme even though it has a different genetic origin from the mammalian examples and has undergone more than 300 million years of independent evolution.      

Death receptor-3 mediates apoptosis in human osteoblasts under narrowly regulated conditions

We previously reported that a soluble form of the TNF-family receptor death receptor-3 (DR3) is expressed in osteoblasts. DR3 regulates death or differentiation in other tissues, and DR3 ligands occur in bone, but the function of DR3 in the osteoblast was unknown. We studied the expression of DR3 and the effects crosslinking antibodies to DR3 or of natural DR3 ligands in human osteoblasts. Western analysis showed that nontransformed osteoblasts and the MG63 osteosarcoma cell line produce both soluble decoy receptor and transmembrane isoforms of DR3. Cell surface labeling showed that low and high DR3-expressing osteoblast populations occur. Verification of by cloning showed a point mutation in DR3 from MG63 cells. Activation of DR3 by antibody crosslinking or with DR3 ligands caused apoptosis in osteoblasts and in MG63 cells, but only in low-density cell cultures. In dense cultures apoptosis did not occur, but nuclear factor-kappaB nuclear translocation was observed under some conditions. Crosslinking of DR3 in high-density MG63 cultures blocked expression of bone matrix elements. DR3 activation in high-density nontransformed osteoblasts had only minor effects on cell maturation. We conclude that DR3 activation can mediate apoptosis in osteoblasts. Its activity is, however, highly restricted by its soluble ligand-binding isoform and possibly also by alternate survival signals. In the presence of survival signals, DR3 may affect cell maturation although effects on differentiation were clearly seen only in the MG63 transformed cell line.     

CD40 ligand functions non-cell autonomously to promote deletion of self-reactive thymocytes

CD40 ligand (CD40L)-deficient mice have been shown to have a defect in negative selection of self-reactive T cells during thymic development. However, the mechanism by which CD40L promotes deletion of autoreactive thymocytes has not yet been elucidated. We have studied negative selection in response to endogenous superantigens in CD40L-deficient mice and, consistent with previous reports, have found a defect in negative selection in these mice. To test the requirement for expression of CD40L on T cells undergoing negative selection, we have generated chimeric mice in which CD40L wild-type and CD40L-deficient thymocytes coexist. We find that both CD40L wild-type and CD40L-deficient thymocytes undergo equivalent and efficient negative selection when these populations coexist in chimeric mice. These results indicate that CD40L can function in a non-cell-autonomous manner during negative selection. Deletion of superantigen-reactive thymocytes was normal in B7-1/B7-2 double-knockout mice, indicating that CD40-CD40L-dependent negative selection is not solely mediated by B7 up-regulation and facilitation of B7-dependent T cell signaling. Finally, although the absence of CD40-CD40L interactions impairs negative selection of autoreactive CD4(+) and CD8(+) cells during thymic development, we find that self-reactive T cells are deleted in the mature CD4(+) population through a CD40L-independent pathway.     

Maturation versus death of developing double-positive thymocytes reflects competing effects on Bcl-2 expression and can be regulated by the intensity of CD28 costimulation

Immature double-positive (DP) thymocytes mature into CD4(+)CD8(-) cells in response to coengagement of TCR with any of a variety of cell surface "coinducer" receptors, including CD2. In contrast, DP thymocytes are signaled to undergo apoptosis by coengagement of TCR with CD28 costimulatory receptors, but the molecular basis for DP thymocyte apoptosis by TCR plus CD28 coengagement is not known. In the present study, we report that TCR plus CD28 coengagement does not invariably induce DP thymocyte apoptosis but, depending on the intensity of CD28 costimulation, can induce DP thymocyte maturation. We demonstrate that distinct but interacting signal transduction pathways mediate DP thymocyte maturation signals and DP thymocyte apoptotic signals. Specifically, DP maturation signals are transduced by the extracellular signal-related kinase (ERK)/mitogen-activated protein kinase (MAPK) pathway and up-regulate expression of the antiapoptotic protein Bcl-2. In contrast, the apoptotic response stimulated by CD28 costimulatory signals is mediated by ERK/MAPK-independent pathways. Importantly, when TCR-activated thymocytes are simultaneously coengaged by both CD28 and CD2 receptors, CD28 signals can inhibit ERK/MAPK-dependent Bcl-2 protein up-regulation. Thus, there is cross-talk between the signal transduction pathways that transduce apoptotic and maturation responses, enabling CD28-initiated signal transduction pathways to both stimulate DP thymocyte apoptosis and also negatively regulate maturation responses initiated by TCR plus CD2 coengagement.     

The influence of acid on astringency of alum and phenolic compounds

Astringency of aqueous solutions of phenolic compounds (grape seed tannins, tannic acid, catechin and gallic acid) increased upon addition of citric acid, whereas the astringency of alum was reduced. Astringency of alum was decreased equivalently by addition of equi-sour levels of lactic acid, citric acid or hydrochloric acid. The difference between alum and the phenolic compounds is speculated to result from chemical modifications affecting binding of the astringents with oral proteins rather than cognitive differences. Chelation of the aluminum ion in alum by acids reduces its availability for interacting with salivary proteins or epithelial proteins. In contrast, the increased astringency produced upon acidification of phenolic compounds is speculated to result from the pH driven increase in the affinity of the phenols for binding with proteins. These results suggest that alum cannot be used interchangeably with phenolic astringents in psychophysical studies.      

Subpopulations of mouse Lyt-2+ T cells defined by the expression of an Ly-6-linked antigen, B4B2

The production and characterization of a rat mu,kappa monoclonal anti-mouse T cell subset antibody, B4B2, is reported in this paper. B4B2 typing of lymphoid tissues of commonly used inbred mouse strains revealed two types of reactivity patterns. They can be characterized as C57BL/6-like (B6-like) or C3H/He-like (C3H-like). Among B6-like strains, B4B2 recognizes 5 to 10% of spleen cells, 30 to 50% of bone marrow cells, and less than 2 to 3% of thymocytes. In C3H-like strains, B4B2 reacts with less than 1% of spleen cells, 2 to 8% of bone marrow cells, and less than 1% of thymocytes. B4B2 recognizes a T cell subset differentiation antigen expressed by B6-like strains but not by C3H-like strains. Typing of BXH recombinant inbred strains showed linked expression of B4B2 and the Ly-6 antigen. The expression of B4B2 antigen appears to be under codominant control as the median fluorescence distribution of B4B2+ cells in C57BL/6 was approximately twice that of (C57BL/6xC3H)F1. B4B2 was shown to react with approximately 40 to 50% of Lyt-2+ T cells and less than 1% of L3T4+ T cells. No staining of resting or activated B cells by B4B2 was detected. The ratio of B4B2+:Lyt-2+ cells was similar for resting T cells and activated T cells obtained from mitogen-stimulated cultures or mixed lymphocyte cultures. In neonatal spleen, substantially more B4B2+ than Lyt-2+ cells were found. With increasing age, however, a rapid decline in B4B2+ cells and a corresponding increase of Lyt-2+ cells was observed. By approximately 1 mo of age, the relative proportion of these subsets had reversed so that Lyt-2+ cells became more numerous than B4B2+ cells.     

Chromosome spreading of associated transposable elements and ribosomal DNA in the fish Erythrinus erythrinus. Implications for genome change and karyoevolution in fish

Background  

The fish, Erythrinus erythrinus, shows an interpopulation diversity, with four karyomorphs differing by chromosomal number, chromosomal morphology and heteromorphic sex chromosomes. Karyomorph A has a diploid number of 2n = 54 and does not have differentiated sex chromosomes. Karyomorph D has 2n = 52 chromosomes in females and 2n = 51 in males, and it is most likely derived from karyomorph A by the differentiation of a multiple X₁X₂Y sex chromosome system. In this study, we analyzed karyomorphs A and D by means of cytogenetic approaches to evaluate their evolutionary relationship.     

Levels of anti-citrullinated protein antibodies and IgM rheumatoid factor are not associated with outcome in early arthritis patients: a cohort study

Introduction  

To investigate whether baseline levels of anti-citrullinated protein antibody (ACPA) or IgM rheumatoid factor (IgM-RF) and changes in the year thereafter are associated with disease activity, functional and radiographic outcome in early arthritis patients, and provide additional information over baseline autoantibody status.     

Phylogeography of Plathymenia reticulata (Leguminosae) reveals patterns of recent range expansion towards northeastern Brazil and southern Cerrados in Eastern Tropical South America

Little is known about past vegetation dynamics in Eastern Tropical South America (ETSA). Here we describe patterns of chloroplast (cp) DNA variation in Plathymenia reticulata, a widespread tree in the ETSA Atlantic Forest and Cerrado biomes, but not found in the xeromorphic Caatinga. Forty one populations, comprising 220 individuals, were analysed by sequencing the trnS‐trnG and trnL‐trnL‐trnF cpDNA regions. Combined, they resulted in 18 geographically structured haplotypes. The central region of the sampling area, comprising Minas Gerais and Goiás Brazilian states, is a centre of genetic diversity and probably the most longstanding area of the distribution range of the species. In contrast, populations from northeastern Brazil and the southern Cerrados showed very low diversity levels, almost exclusively with common haplotypes which are also found in the central region. Coupled with a long‐branched star‐like network, these patterns suggest a recent range expansion of P. reticulata to those regions from central region sources. The recent origin of the species (in the early Pleistocene) or the extinction of some populations due to drier and cooler climate during the last glacial maximum could have been responsible for that phylogeographic pattern. The populations from northeastern Brazil originated from two colonization routes, one eastern (Atlantic) and one western (inland). Due to its high diversity and complex landscape, the central region, especially central‐north Minas Gerais (between 15°–18° S and 42°–46° W), should be given the highest priority for conservation.