Synaptic defects in ataxia mice result from a mutation in Usp14, encoding a ubiquitin-specific protease

Mice that are homozygous with respect to a mutation (ax(J)) in the ataxia (ax) gene develop severe tremors by 2-3 weeks of age followed by hindlimb paralysis and death by 6-10 weeks of age. Here we show that ax encodes ubiquitin-specific protease 14 (Usp14). Ubiquitin proteases are a large family of cysteine proteases that specifically cleave ubiquitin conjugates. Although Usp14 can cleave a ubiquitin-tagged protein in vitro, it is unable to process polyubiquitin, which is believed to be associated with the protein aggregates seen in Parkinson disease, spinocerebellar ataxia type 1 (SCA1; ref. 4) and gracile axonal dystrophy (GAD). The physiological substrate of Usp14 may therefore contain a mono-ubiquitin side chain, the removal of which would regulate processes such as protein localization and protein activity. Expression of Usp14 is significantly altered in ax(J)/ax(J) mice as a result of the insertion of an intracisternal-A particle (IAP) into intron 5 of Usp14. In contrast to other neurodegenerative disorders such as Parkinson disease and SCA1 in humans and GAD in mice, neither ubiquitin-positive protein aggregates nor neuronal cell loss is detectable in the central nervous system (CNS) of ax(J) mice. Instead, ax(J) mice have defects in synaptic transmission in both the central and peripheral nervous systems. These results suggest that ubiquitin proteases are important in regulating synaptic activity in mammals.     

RICK/Rip2/CARDIAK mediates signalling for receptors of the innate and adaptive immune systems

The immune system consists of two evolutionarily different but closely related responses, innate immunity and adaptive immunity. Each of these responses has characteristic receptors-Toll-like receptors (TLRs) for innate immunity and antigen-specific receptors for adaptive immunity. Here we show that the caspase recruitment domain (CARD)-containing serine/threonine kinase Rip2 (also known as RICK, CARDIAK, CCK and Ripk2) transduces signals from receptors of both immune responses. Rip2 was recruited to TLR2 signalling complexes after ligand stimulation. Moreover, cytokine production in Rip2-deficient cells was reduced on stimulation of TLRs with lipopolysaccharide, peptidoglycan and double-stranded RNA, but not with bacterial DNA, indicating that Rip2 is downstream of TLR2/3/4 but not TLR9. Rip2-deficient cells were also hyporesponsive to signalling through interleukin (IL)-1 and IL-18 receptors, and deficient for signalling through Nod proteins-molecules also implicated in the innate immune response. Furthermore, Rip2-deficient T cells showed severely reduced NF-kappaB activation, IL-2 production and proliferation on T-cell-receptor (TCR) engagement, and impaired differentiation to T-helper subtype 1 (TH1) cells, indicating that Rip2 is required for optimal TCR signalling and T-cell differentiation. Rip2 is therefore a signal transducer and integrator of signals for both the innate and adaptive immune systems.     

Functional genomic analysis of phagocytosis and identification of a Drosophila receptor for E. coli

The recognition and phagocytosis of microbes by macrophages is a principal aspect of innate immunity that is conserved from insects to humans. Drosophila melanogaster has circulating macrophages that phagocytose microbes similarly to mammalian macrophages, suggesting that insect macrophages can be used as a model to study cell-mediated innate immunity. We devised a double-stranded RNA interference-based screen in macrophage-like Drosophila S2 cells, and have defined 34 gene products involved in phagocytosis. These include proteins that participate in haemocyte development, vesicle transport, actin cytoskeleton regulation and a cell surface receptor. This receptor, Peptidoglycan recognition protein LC (PGRP-LC), is involved in phagocytosis of Gram-negative but not Gram-positive bacteria. Drosophila humoral immunity also distinguishes between Gram-negative and Gram-positive bacteria through the Imd and Toll pathways, respectively; however, a receptor for the Imd pathway has not been identified. Here we show that PGRP-LC is important for antibacterial peptide synthesis induced by Escherichia coli both in vitro and in vivo. Furthermore, totem mutants, which fail to express PGRP-LC, are susceptible to Gram-negative (E. coli), but not Gram-positive, bacterial infection. Our results demonstrate that PGRP-LC is an essential component for recognition and signalling of Gram-negative bacteria. Furthermore, this functional genomic approach is likely to have applications beyond phagocytosis.     

ICOS co-stimulatory receptor is essential for T-cell activation and function

T-lymphocyte activation and immune function are regulated by co-stimulatory molecules. CD28, a receptor for B7 gene products, has a chief role in initiating T-cell immune responses. CTLA4, which binds B7 with a higher affinity, is induced after T-cell activation and is involved in downregulating T-cell responses. The inducible co-stimulatory molecule (ICOS), a third member of the CD28/CTLA4 family, is expressed on activated T cells. Its ligand B7H/B7RP-1 is expressed on B cells and in non-immune tissues after injection of lipopolysaccharide into animals. To understand the role of ICOS in T-cell activation and function, we generated and analysed ICOS-deficient mice. Here we show that T-cell activation and proliferation are defective in the absence of ICOS. In addition, ICOS -/- T cells fail to produce interleukin-4 when differentiated in vitro or when primed in vivo. ICOS is required for humoral immune responses after immunization with several antigens. ICOS-/- mice showed greatly enhanced susceptibility to experimental autoimmune encephalomyelitis, indicating that ICOS has a protective role in inflammatory autoimmune diseases.     

Gulliver's travels in HIVland

The emergence of HIV and AIDS is narrated here through the eyes of the legendary Irish traveller Gulliver, observing the replication, cross-species origin, evolution, diversity and transmission of HIV. Ethical problems of vaccine trials, the social impact of AIDS, and prospects for its prevention, including the development of topical virucidal lotions, are discussed. The existence of a growing proportion of HIV-infected, immunocompromised children and adults may significantly affect current immunization programmes and the evolution of opportunistic infections.     

Structure of the Ku heterodimer bound to DNA and its implications for double-strand break repair

The Ku heterodimer (Ku70 and Ku80 subunits) contributes to genomic integrity through its ability to bind DNA double-strand breaks and facilitate repair by the non-homologous end-joining pathway. The crystal structure of the human Ku heterodimer was determined both alone and bound to a 55-nucleotide DNA element at 2.7 and 2.5 A resolution, respectively. Ku70 and Ku80 share a common topology and form a dyad-symmetrical molecule with a preformed ring that encircles duplex DNA. The binding site can cradle two full turns of DNA while encircling only the central 3-4 base pairs (bp). Ku makes no contacts with DNA bases and few with the sugar-phosphate backbone, but it fits sterically to major and minor groove contours so as to position the DNA helix in a defined path through the protein ring. These features seem well designed to structurally support broken DNA ends and to bring the DNA helix into phase across the junction during end processing and ligation.     

Ecology. Global amphibian population declines

The decline and disappearance of relatively undisturbed populations of amphibians in several high-altitude regions since the 1970s suggests that they may have suffered a global decline, perhaps with a common cause or causes. Houlahan et al. examined means of trends for 936 amphibian populations and concluded that global declines began in the late 1950s, peaked in the 1960s, and have continued at a reduced rate since. Here we re-analyse their data using a method that accounts for the sampling of different populations over different time periods, and find evidence of a mean global decline in monitored populations only in the 1990s. However it is calculated, the global mean not only masks substantial spatial and temporal variation in population trends and sampling effort, but also fails to distinguish between a global decline with global causes and the cumulative effects of local declines with local causes.