Bone marrow cells give rise to distinct cell clones within the thymus

The thymus is the major, if not the sole site of maturation of T lymphocytes from their haematopoietic precursors. During embryonic life (at a few well-defined intervals, at least in birds) the thymus receives thymus-homing haematopoietic precursors that give rise to antigen-specific functional T lymphocytes. Although the number and thymic location of distinct T-cell lineages destined to form the peripheral T-cell pool are not yet well defined, at least two independent pathways have been proposed. First, thymic subcapsular lymphoblasts divide and differentiate to give rise to small deep cortical thymic lymphocytes, medullary lymphocytes and thymus emigrants (I.W., unpublished data) and second, the medulla contains an independent self-renewing population that contains the precursors of the peripheral T-cell pool. Following irradiation the thymus may be repopulated by injected haematopoietic cells presumably related to the thymus-homing haematopoietic cells of the embryo. Here we have reconstituted irradiated mice with limiting numbers of bone marrow cells from Thy-1 congeneic donors and have found distinct clones of cells within the thymus. The pattern of reconstitution by the precursor cells indicates that two independent thymus lineages exist: cortex plus medulla, and medulla alone.     

A tissue-specific endothelial cell molecule involved in lymphocyte homing

An endothelial cell surface molecule that is selectively expressed in mucosal organs is required for lymphocyte homing to mucosal lymphoid tissues. This 'vascular addressin' appears to function as a tissue-specific marker or address signal for recognition by lymphocytes circulating in the blood.     

Broad phylogenomic sampling improves resolution of the animal tree of life

Long-held ideas regarding the evolutionary relationships among animals have recently been upended by sometimes controversial hypotheses based largely on insights from molecular data. These new hypotheses include a clade of moulting animals (Ecdysozoa) and the close relationship of the lophophorates to molluscs and annelids (Lophotrochozoa). Many relationships remain disputed, including those that are required to polarize key features of character evolution, and support for deep nodes is often low. Phylogenomic approaches, which use data from many genes, have shown promise for resolving deep animal relationships, but are hindered by a lack of data from many important groups. Here we report a total of 39.9 Mb of expressed sequence tags from 29 animals belonging to 21 phyla, including 11 phyla previously lacking genomic or expressed-sequence-tag data. Analysed in combination with existing sequences, our data reinforce several previously identified clades that split deeply in the animal tree (including Protostomia, Ecdysozoa and Lophotrochozoa), unambiguously resolve multiple long-standing issues for which there was strong conflicting support in earlier studies with less data (such as velvet worms rather than tardigrades as the sister group of arthropods), and provide molecular support for the monophyly of molluscs, a group long recognized by morphologists. In addition, we find strong support for several new hypotheses. These include a clade that unites annelids (including sipunculans and echiurans) with nemerteans, phoronids and brachiopods, molluscs as sister to that assemblage, and the placement of ctenophores as the earliest diverging extant multicellular animals. A single origin of spiral cleavage (with subsequent losses) is inferred from well-supported nodes. Many relationships between a stable subset of taxa find strong support, and a diminishing number of lineages remain recalcitrant to placement on the tree.     

Destruction of virus infected cells by neutrophils and complement

The paper describes an antibody independent mechanism of cytotoxicity whereby virus infected but not uninfected cells are destroyed by the combined presence of neutrophils and complement.     

Interneuronal barrages and ripple superposed on inhibitory postsynaptic potentials

Résumé L'activité électrique des neurones du noyau thalamique ventro-latéral est étudiée ici chez des chats anesthésiés au nembutal et immobilisés avec du flaxedil au moyen d'un enregistrement intracellulaire. Nous avons observé que l'enregistrement de certains neurones montre que le potentiel nommé inhibiteur postsynaptique (IPSP) est accompagné de la décharge en barrage d'un autre neurone probablement semblable à la cellule deRenshaw.

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We thank Mr.G. Bilanow for invaluable technical help.     

Destruction of virus infected cells by neutrophils and complement

Summary The paper describes an antibody independent mechanism of cytotoxicity whereby virus infected but not uninfected cells are destroyed by the combined presence of neutrophils and complement.Supported by A.I. 14981 and by the MRC of Canada.Acknowledgment. We thank C.J. Wust for invaluable discussions.     

SLX4, a coordinator of structure-specific endonucleases, is mutated in a new Fanconi anemia subtype

DNA interstrand crosslink repair requires several classes of proteins, including structure-specific endonucleases and Fanconi anemia proteins. SLX4, which coordinates three separate endonucleases, was recently recognized as an important regulator of DNA repair. Here we report the first human individuals found to have biallelic mutations in SLX4. These individuals, who were previously diagnosed as having Fanconi anemia, add SLX4 as an essential component to the FA-BRCA genome maintenance pathway.