山西垣曲盆地始新世轮藻植物群

记述山西垣曲盆地河堤组任村至寨组里段轮藻化石,计１１属,１４种,２未定种,建立了一个地区性轮藻化石组合：Ｒａｓｋｙｅｌｌａｓｉｎｅｎｓｉｓ－Ｌｉｎｙｉｅｃｈａｒａｄｅｃｏｒｏｓａ－Ｓｔｅｐｈａｎｏｃｈａｒａｇｌｏｂｕｌａ组合,该组合位于中国早第三纪轮藻植物群序列中Ｏｂｔｕｓｏｃｈａｒａｊｉａｎｇｌｉｎｇｅｎｓｉｓ－Ｇｙｒｏｇｏｎａｑｉａｎｊｉａｎｇｉｃａ植物群的上部,轮藻植物群反映的地质时代始新世     

Converting human skin cells to neurons: a new tool to study and treat brain disorders?

Recent publications in Cell Stem Cell (Son et?al., 2011; Ambasudhan et?al., 2011), PNAS (Pfisterer et?al., 2011), and Nature (Caiazzo et?al., 2011; Pang et?al., 2011; Yoo et?al., 2011) report that functional neurons can be directly generated from human fibroblast cells without going through the pluripotent state.     

Pleurotus eryngii species complex: sequence analysis and phylogeny based on partial EF1α and RPB2 genes

The Pleurotus eryngii species complex comprises at least six varieties (var. eryngii (DC.: Fr) Quel., ferulae Lanzi, elaeoselini Venturella et?al., nebrodensis (Inzenga) Sacc., tingitanus Lewinsohn et?al. and tuoliensis C.J. Mou). This species is unique among the genus Pleurotus because in nature it is found in association with certain species of the Apiaceae (Umbelliferae) and Asteraceae (Compositae) families. Sequences of partial regions of the translation elongation factor (EF1α) and RNA polymerase II (RPB2) genes were analyzed in order to detect nucleotide polymorphisms that might unequivocally distinguish varieties eryngii, ferulae, elaeoselini and nebrodensis. A phylogenetic analysis was also performed with an aim to establish phylogenetic relationships among those. Sequence analysis of the partial EF1α and RPB2 genes contained nucleotide polymorphisms able to unequivocally distinguish variety nebrodensis from the rest. However, distinction among eryngii, elaeoselini and ferulae was achieved only through the RPB2 gene. The phylogenetic analyses from the combined data sets (EF1α and RPB2) indicated that P. eryngii is a monophyletic group and that varieties eryngii, elaeoselini and ferulae are closely related. P. eryngii var. nebrodensis was placed in a distinct clade clearly differentiated from the other varieties but still monophyletic with the P. eryngii complex. The limited nucleotide variation in partial EF1α and RPB2 among varieties eryngii, ferulae and elaeoselini supports the placement of these groups as varieties and not species within the complex.     

Malaria: a peek at the var variorum

Geneticists encountering the diversity of the malaria parasite's var gene family for the first time often complain that its complexity is a nightmare. A new article by Barry et al. presents the latest and most systematic attempt to date to decipher the var variorum. This important work, combined with other recent articles on var global variation such as that by Kraemer et al., suggests that only the tip of the var diversity iceberg is currently in view. In this article, we discuss these recent results and provide an overview of current understanding of var diversity.     

iPSCs: induced back to controversy

Several recent reports (Mayshar et?al., 2010; Laurent et?al., 2011; Lister et?al., 2011; Gore et?al., 2011; Hussein et?al., 2011) uncover genetic and epigenetic alterations in induced pluripotent stem cells, stimulating debate about their future. However, will these important findings really impact what we hope to gain?     

Structural basis for binding of Plasmodium falciparum erythrocyte membrane protein 1 to chondroitin sulfate and placental tissue and the influence of protein polymorphisms on binding specificity

Chondroitin sulfate (CS) A is a key receptor for adhesion of Plasmodium falciparum-infected erythrocytes (IEs) in the placenta and can also mediate adhesion to microvascular endothelial cells. IEs that adhere to CSA express var2csa-type genes, which encode specific variants of the IE surface antigen P. falciparum erythrocyte membrane protein 1 (PfEMP1). We report direct binding of native PfEMP1, isolated from IEs and encoded by var2csa, to immobilized CSA. Binding of PfEMP1 was dependent on 4-O-sulfated disaccharides and glucuronic acid rather than iduronic acid, consistent with the specificity of intact IEs. Using immobilized CS oligosaccharides as neoglycolipid probes, the minimum chain length for direct binding of PfEMP1 was eight monosaccharide units. Similarly for IE adhesion to placental tissue there was a requirement for 4-O-sulfated GalNAc and glucuronic acid mixed with non-sulfated disaccharides; 6-O-sulfation interfered with the interaction between placental CSA and IEs. The minimum chain length for maximal inhibition of adhesion was 10 monosaccharide residues. Partially 4-O-sulfated CS oligosaccharides (45-55% sulfation) were highly effective inhibitors of placental adhesion (IC(50), 0.15 microg/ml) and may have potential for therapeutic development. We used defined P. falciparum isolates expressing different variants of var2csa in adhesion assays and found that there were isolate-specific differences in the preferred structural motifs for adhesion to CSA that correlated with polymorphisms in PfEMP1 encoded by var2csa-type genes. This may influence sites of IE sequestration or parasite virulence. These findings have significant implications for understanding the pathogenesis and biology of malaria, particularly during pregnancy, and the development of targeted interventions.     

Genetic diversity of expressed Plasmodium falciparum var genes from Tanzanian children with severe malaria

ABSTRACT: BACKGROUND: Severe malaria has been attributed to the expression of a restricted subset of the var multigene family, which encodes for Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1). PfEMP1 mediates cytoadherence and sequestration of infected erythrocytes into the post-capillary venules of the vital organs such as the brain, lung or placenta. Var genes are highly diverse and can be classified in three major groups (ups A, B and C) and two intermediate groups (B/A and B/C) based on the genomic location, gene orientation and upstream sequences. The genetic diversity of expressed var genes in relation to severity of disease in Tanzanian children was analysed. METHODS: Children with defined severe (SM) and asymptomatic malaria (AM) were recruited. Fulllength var mRNA was isolated and reversed transcribed into var cDNA. Subsequently, the DBL and N-terminal domains, and up-stream sequences were PCR amplified, cloned and sequenced. Sequences derived from SM and AM isolates were compared and analysed. RESULTS: The analysis confirmed that the var family is highly diverse in natural Plasmodium falciparum populations. Sequence diversity of amplified var DBL-1alpha and upstream regions showed minimal overlap among isolates, implying that the var gene repertoire is vast and most probably indefinite in endemic areas. var DBL-1alpha sequences from AM isolates were more diverse with more singletons found (p<0.05) than those from SM infections. Furthermore, few var DBL-1alpha sequences from SM patients were rare and restricted suggesting that certain PfEMP1 variants might induce severe disease. CONCLUSIONS: The genetic sequence diversity of var genes of P. falciparum isolates from Tanzanian children is large and its relationship to disease severity has been studied. Observed differences suggest that different var genes might have fundamentally different roles in the host-parasite interaction. Further research is required to examine clear disease-associations of var gene subsets in different geographical settings. The importance of very strict clinical definitions and appropriate large control groups needs to be emphasized for future studies on disease associations of PfEMP1.     

Induction of Strain-Transcending Antibodies Against Group A PfEMP1 Surface Antigens from Virulent Malaria Parasites

Sequence diversity in pathogen antigens is an obstacle to the development of interventions against many infectious diseases. In malaria caused by Plasmodium falciparum, the PfEMP1 family of variant surface antigens encoded by var genes are adhesion molecules that play a pivotal role in malaria pathogenesis and clinical disease. PfEMP1 is a major target of protective immunity, however, development of drugs or vaccines based on PfEMP1 is problematic due to extensive sequence diversity within the PfEMP1 family. Here we identified the PfEMP1 variants transcribed by P. falciparum strains selected for a virulence-associated adhesion phenotype (IgM-positive rosetting). The parasites transcribed a subset of Group A PfEMP1 variants characterised by an unusual PfEMP1 architecture and a distinct N-terminal domain (either DBLα1.5 or DBLα1.8 type). Antibodies raised in rabbits against the N-terminal domains showed functional activity (surface reactivity with live infected erythrocytes (IEs), rosette inhibition and induction of phagocytosis of IEs) down to low concentrations (<10 µg/ml of total IgG) against homologous parasites. Furthermore, the antibodies showed broad cross-reactivity against heterologous parasite strains with the same rosetting phenotype, including clinical isolates from four sub-Saharan African countries that showed surface reactivity with either DBLα1.5 antibodies (variant HB3var6) or DBLα1.8 antibodies (variant TM284var1). These data show that parasites with a virulence-associated adhesion phenotype share IE surface epitopes that can be targeted by strain-transcending antibodies to PfEMP1. The existence of shared surface epitopes amongst functionally similar disease-associated P. falciparum parasite isolates suggests that development of therapeutic interventions to prevent severe malaria is a realistic goal.     

A family affair: var genes, PfEMP1 binding, and malaria disease

An immunovariant adhesion protein family in Plasmodium falciparum named erythrocyte membrane protein 1 (PfEMP1), encoded by var genes, is responsible for both antigenic variation and cytoadhesion of infected erythrocytes at blood microvasculature sites throughout the body. Elucidation of the genome sequence of P. falciparum has revealed that var genes can be classified into different groups, each with distinct 5' flanking sequences, chromosomal locations and gene orientations. Recent binding and serological comparisons suggest that this genomic organization might cause var genes to diversify into separately recombining adhesion groups that have different roles in infection and disease. Detailed understanding of PfEMP1 expression and receptor binding mechanisms during infection and of the antigenic relatedness of disease variants might lead to new approaches in prevention of malaria disease.     

Cullin RING Ligases: Glommed by Glomulin

Cullin ring ligases (CRLs) constitute the largest group of RING finger ubiquitin ligases. Two recent studies in?Molecular Cell describe glomulin as a CRL1 inhibitor that blocks interactions with its ubiquitin-conjugating enzyme (E2) (Duda et?al., 2012; Tron et?al., 2012). These findings and their significance are discussed.     

Moving right along: how PP1 helps clear the checkpoint

Spindle checkpoint silencing is crucial for cell-cycle progression, but mechanisms underlying this process remain mysterious. Two papers, one in this issue of Developmental Cell (Meadows et?al., 2011) and one in Current Biology (Rosenberg et?al., 2011), begin to show how phosphatase PP1-gamma connects chromosome-microtubule attachment with anaphase entry.