Generation of a functional mammary gland from a single stem cell

The existence of mammary stem cells (MaSCs) has been postulated from evidence that the mammary gland can be regenerated by transplantation of epithelial fragments in mice. Interest in MaSCs has been further stimulated by their potential role in breast tumorigenesis. However, the identity and purification of MaSCs has proved elusive owing to the lack of defined markers. We isolated discrete populations of mouse mammary cells on the basis of cell-surface markers and identified a subpopulation (Lin-CD29hiCD24+) that is highly enriched for MaSCs by transplantation. Here we show that a single cell, marked with a LacZ transgene, can reconstitute a complete mammary gland in vivo. The transplanted cell contributed to both the luminal and myoepithelial lineages and generated functional lobuloalveolar units during pregnancy. The self-renewing capacity of these cells was demonstrated by serial transplantation of clonal outgrowths. In support of a potential role for MaSCs in breast cancer, the stem-cell-enriched subpopulation was expanded in premalignant mammary tissue from MMTV-wnt-1 mice and contained a higher number of MaSCs. Our data establish that single cells within the Lin-CD29hiCD24+ population are multipotent and self-renewing, properties that define them as MaSCs.     

PD-1 expression on HIV-specific T cells is associated with T-cell exhaustion and disease progression

Functional impairment of T cells is characteristic of many chronic mouse and human viral infections. The inhibitory receptor programmed death 1 (PD-1; also known as PDCD1), a negative regulator of activated T cells, is markedly upregulated on the surface of exhausted virus-specific CD8 T cells in mice. Blockade of this pathway using antibodies against the PD ligand 1 (PD-L1, also known as CD274) restores CD8 T-cell function and reduces viral load. To investigate the role of PD-1 in a chronic human viral infection, we examined PD-1 expression on human immunodeficiency virus (HIV)-specific CD8 T cells in 71 clade-C-infected people who were naive to anti-HIV treatments, using ten major histocompatibility complex (MHC) class I tetramers specific for frequently targeted epitopes. Here we report that PD-1 is significantly upregulated on these cells, and expression correlates with impaired HIV-specific CD8 T-cell function as well as predictors of disease progression: positively with plasma viral load and inversely with CD4 T-cell count. PD-1 expression on CD4 T cells likewise showed a positive correlation with viral load and an inverse correlation with CD4 T-cell count, and blockade of the pathway augmented HIV-specific CD4 and CD8 T-cell function. These data indicate that the immunoregulatory PD-1/PD-L1 pathway is operative during a persistent viral infection in humans, and define a reversible defect in HIV-specific T-cell function. Moreover, this pathway of reversible T-cell impairment provides a potential target for enhancing the function of exhausted T cells in chronic HIV infection.     

Restoring function in exhausted CD8 T cells during chronic viral infection

Functional impairment of antigen-specific T cells is a defining characteristic of many chronic infections, but the underlying mechanisms of T-cell dysfunction are not well understood. To address this question, we analysed genes expressed in functionally impaired virus-specific CD8 T cells present in mice chronically infected with lymphocytic choriomeningitis virus (LCMV), and compared these with the gene profile of functional memory CD8 T cells. Here we report that PD-1 (programmed death 1; also known as Pdcd1) was selectively upregulated by the exhausted T cells, and that in vivo administration of antibodies that blocked the interaction of this inhibitory receptor with its ligand, PD-L1 (also known as B7-H1), enhanced T-cell responses. Notably, we found that even in persistently infected mice that were lacking CD4 T-cell help, blockade of the PD-1/PD-L1 inhibitory pathway had a beneficial effect on the 'helpless' CD8 T cells, restoring their ability to undergo proliferation, secrete cytokines, kill infected cells and decrease viral load. Blockade of the CTLA-4 (cytotoxic T-lymphocyte-associated protein 4) inhibitory pathway had no effect on either T-cell function or viral control. These studies identify a specific mechanism of T-cell exhaustion and define a potentially effective immunological strategy for the treatment of chronic viral infections.     

Haemangioblast commitment is initiated in the primitive streak of the mouse embryo

Haematopoietic and vascular cells are thought to arise from a common progenitor called the haemangioblast. Support for this concept has been provided by embryonic stem (ES) cell differentiation studies that identified the blast colony-forming cell (BL-CFC), a progenitor with both haematopoietic and vascular potential. Using conditions that support the growth of BL-CFCs, we identify comparable progenitors that can form blast cell colonies (displaying haematopoietic and vascular potential) in gastrulating mouse embryos. Cell mixing and limiting dilution analyses provide evidence that these colonies are clonal, indicating that they develop from a progenitor with haemangioblast potential. Embryo-derived haemangioblasts are first detected at the mid-streak stage of gastrulation and peak in number during the neural plate stage. Analysis of embryos carrying complementary DNA of the green fluorescent protein targeted to the brachyury locus demonstrates that the haemangioblast is a subpopulation of mesoderm that co-expresses brachyury (also known as T) and Flk-1 (also known as Kdr). Detailed mapping studies reveal that haemangioblasts are found at highest frequency in the posterior region of the primitive streak, indicating that initial stages of haematopoietic and vascular commitment occur before blood island development in the yolk sac.     

Genome sequence of Bacillus cereus and comparative analysis with Bacillus anthracis

Bacillus cereus is an opportunistic pathogen causing food poisoning manifested by diarrhoeal or emetic syndromes. It is closely related to the animal and human pathogen Bacillus anthracis and the insect pathogen Bacillus thuringiensis, the former being used as a biological weapon and the latter as a pesticide. B. anthracis and B. thuringiensis are readily distinguished from B. cereus by the presence of plasmid-borne specific toxins (B. anthracis and B. thuringiensis) and capsule (B. anthracis). But phylogenetic studies based on the analysis of chromosomal genes bring controversial results, and it is unclear whether B. cereus, B. anthracis and B. thuringiensis are varieties of the same species or different species. Here we report the sequencing and analysis of the type strain B. cereus ATCC 14579. The complete genome sequence of B. cereus ATCC 14579 together with the gapped genome of B. anthracis A2012 enables us to perform comparative analysis, and hence to identify the genes that are conserved between B. cereus and B. anthracis, and the genes that are unique for each species. We use the former to clarify the phylogeny of the cereus group, and the latter to determine plasmid-independent species-specific markers.     

The infinite and infinitesimal quantities of du Bois-Reymond and their reception

The mixed fortunes of Paul du Bois-Reymond's infinitary calculus and ideal boundary between convergence and divergence are traced from 1870 to 1914. Cantor, Dedekind, Peano, Russell, Pringsheim and others objected. Stolz, Borel, Hardy and others accepted, at least in part, and built further. Hausdorff to some extent effected a compromise. The differing attitudes of the different participants toward infinitesimals and infinitely large quantities are described. In addition to shedding some light on the status of infinites, the whole story serves as a study of mathematical change, and shows that the proof-refutation process described by Lakatos is only one aspect of mathematical development. The story also sheds some light on the rise of 20^th century functional analysis, algebra and topology.Wer je den grossen Bau der Welt bedacht und fühlte nicht, wie Gottes hoher Geist noch über den Gesetzen wacht und kreist-wie blind erscheint, wer Schöpfertum verlacht! Wir kennen kaum den kleinsten Teil davon: Gesetz ist Wunder, Zahl ist Weltenton. Albrecht Haushofer, Moabit Sonnets, 1944, LXIX, Kosmos     

Distribution, movements, and habitat use of razorback sucker ( Xyrauchen texanus ) in a lower Colorado River reservoir, Arizona-Nevada

Distribution, movements, and habitat use of 10 wild adult razorback suckers ( Xyrauchen texanus ) were examined in Lake Mohave, Arizona-Nevada, from November 1994 through July 1997. Movement rates (0.00-17.35 km d -1 ) and ranges ( x = 39 km) were similar to those for riverine populations. All study fish returned to spawning sites used in previous years, but they also visited other spawning areas. Spawning females were significantly ( P = 0.031) more active than males (480 vs. 87 m d -1 ) and moved substantial distances between spawning sites during peak reproduction (1-28 February). Fish became most active (m d -1 , km month -1 ) after spawning and moved to areas known to support higher algal production. Fish were typically within 50 m ( P 30.0 m). Adults were detected throughout the available thermal gradient (12°-30°C), but during summer typically had body temperatures between 18° and 22°C. Vertical movements within the water column showed no correlation with depth or time of day, but seasonal shifts suggest fish may regulate body temperature by seeking specific temperatures during reservoir stratification.     

Genomic sequencing of colorectal adenocarcinomas identifies a recurrent VTI1A-TCF7L2 fusion

Prior studies have identified recurrent oncogenic mutations in colorectal adenocarcinoma and have surveyed exons of protein-coding genes for mutations in 11 affected individuals. Here we report whole-genome sequencing from nine individuals with colorectal cancer, including primary colorectal tumors and matched adjacent non-tumor tissues, at an average of 30.7× and 31.9× coverage, respectively. We identify an average of 75 somatic rearrangements per tumor, including complex networks of translocations between pairs of chromosomes. Eleven rearrangements encode predicted in-frame fusion proteins, including a fusion of VTI1A and TCF7L2 found in 3 out of 97 colorectal cancers. Although TCF7L2 encodes TCF4, which cooperates with β-catenin in colorectal carcinogenesis, the fusion lacks the TCF4 β-catenin-binding domain. We found a colorectal carcinoma cell line harboring the fusion gene to be dependent on VTI1A-TCF7L2 for anchorage-independent growth using RNA interference-mediated knockdown. This study shows previously unidentified levels of genomic rearrangements in colorectal carcinoma that can lead to essential gene fusions and other oncogenic events.