Pre-mRNA splicing and mRNA export linked by direct interactions between UAP56 and Aly.

Recent studies indicate that splicing of pre-messenger RNA and export of mRNA are normally coupled in vivo. During splicing, the conserved mRNA export factor Aly is recruited to the spliced mRNA-protein complex (mRNP), which targets the mRNA for export. At present, it is not known how Aly is recruited to the spliced mRNP. Here we show that the conserved DEAD-box helicase UAP56, which functions during spliceosome assembly, interacts directly and highly specifically with Aly. Moreover, UAP56 is present together with Aly in the spliced mRNP. Significantly, excess UAP56 is a potent dominant negative inhibitor of mRNA export. Excess UAP56 also inhibits the recruitment of Aly to the spliced mRNP. Furthermore, a mutation in Aly that blocks its interaction with UAP56 prevents recruitment of Aly to the spliced mRNP. These data suggest that the splicing factor UAP56 functions in coupling the splicing and export machineries by recruiting Aly to the spliced mRNP.     

Stimulated platelets use serotonin to enhance their retention of procoagulant proteins on the cell surface.

Activated platelets bind numerous adhesive and procoagulant proteins by receptor-mediated processes. Although there is little evidence to suggest that these processes are heterogeneous in platelets, we previously found that platelets co-stimulated with collagen and thrombin express functional alpha-granule factor V only on a subpopulation of cells. Here we show that these cells, referred to as 'COAT-platelets', bind additional alpha-granule proteins, including fibrinogen, von Willebrand factor, thrombospondin, fibronectin and alpha2-antiplasmin. These proteins are all transglutaminase substrates, and inhibitors of transglutaminase prevent the production of COAT-platelets. A synthetic transglutaminase substrate (CP15) also binds to COAT-platelets, and analysis by high performance liquid chromatography/mass spectrometry shows that a product is formed with a relative molecular mass (Mr) equal to CP15 plus 176. Serotonin, an abundant component of platelet-dense granules, has an Mr of 176, and fibrinogen isolated from COAT-platelets contains covalently linked serotonin. Synthetic bovine serum albumin-(serotonin)6 binds selectively to COAT-platelets and also inhibits the retention of procoagulant proteins on COAT-platelets. These data indicate that COAT-platelets use serotonin conjugation to augment the retention of procoagulant proteins on their cell surface through an as yet unidentified serotonin receptor.     

Hormonal stimulation of adenylyl cyclase through Gi-protein beta gamma subunits.

Agonist-bound receptors activate heterotrimeric (alpha beta gamma) G proteins by catalysing replacement by GTP of GDP bound to the alpha subunit, resulting in dissociation of alpha-GTP from the beta gamma subunits. In most cases, alpha-GTP carries the signal to effectors, as in hormonal stimulation and inhibition of adenylyl cyclase by alpha s and alpha i respectively. By contrast, genetic evidence in yeast and studies in mammalian cells suggest that beta gamma subunits of G proteins may also regulate effector pathways. Indeed, of the four recombinant mammalian adenylyl cyclases available for study, two, adenylyl cyclases II and IV, are stimulated by beta gamma. This effect of beta gamma requires costimulation by alpha s-GTP. This conditional pattern of effector responsiveness led to the prediction that receptors coupled to many G proteins will mediate elevation of cellular cyclic AMP, provided that Gs is also active. We now confirm this prediction. Coexpression of mutationally active alpha s with adenylyl cyclase II converted agonists that act through 'inhibitory' receptors (coupled to Gi) into stimulators of cAMP synthesis. Experiments using pertussis toxin and a putative scavenger of beta gamma, the alpha subunit of transducin, suggest that beta gamma subunits of the Gi proteins mediated this stimulation. These findings assign a new signalling function to beta gamma subunits of Gi proteins, the conditional stimulation of cAMP synthesis by adenylyl cyclase II.     

Mast cells are essential intermediaries in regulatory T-cell tolerance

Contrary to the proinflammatory role of mast cells in allergic disorders, the results obtained in this study establish that mast cells are essential in CD4+CD25+Foxp3+ regulatory T (T(Reg))-cell-dependent peripheral tolerance. Here we confirm that tolerant allografts, which are sustained owing to the immunosuppressive effects of T(Reg) cells, acquire a unique genetic signature dominated by the expression of mast-cell-gene products. We also show that mast cells are crucial for allograft tolerance, through the inability to induce tolerance in mast-cell-deficient mice. High levels of interleukin (IL)-9--a mast cell growth and activation factor--are produced by activated T(Reg) cells, and IL-9 production seems important in mast cell recruitment to, and activation in, tolerant tissue. Our data indicate that IL-9 represents the functional link through which activated T(Reg) cells recruit and activate mast cells to mediate regional immune suppression, because neutralization of IL-9 greatly accelerates allograft rejection in tolerant mice. Finally, immunohistochemical analysis clearly demonstrates the existence of this novel T(Reg)-IL-9-mast cell relationship within tolerant allografts.     

A juvenile early hominin skeleton from Dikika, Ethiopia

Understanding changes in ontogenetic development is central to the study of human evolution. With the exception of Neanderthals, the growth patterns of fossil hominins have not been studied comprehensively because the fossil record currently lacks specimens that document both cranial and postcranial development at young ontogenetic stages. Here we describe a well-preserved 3.3-million-year-old juvenile partial skeleton of Australopithecus afarensis discovered in the Dikika research area of Ethiopia. The skull of the approximately three-year-old presumed female shows that most features diagnostic of the species are evident even at this early stage of development. The find includes many previously unknown skeletal elements from the Pliocene hominin record, including a hyoid bone that has a typical African ape morphology. The foot and other evidence from the lower limb provide clear evidence for bipedal locomotion, but the gorilla-like scapula and long and curved manual phalanges raise new questions about the importance of arboreal behaviour in the A. afarensis locomotor repertoire.