Sortilin is essential for proNGF-induced neuronal cell death

Sortilin (approximately 95 kDa) is a member of the recently discovered family of Vps10p-domain receptors, and is expressed in a variety of tissues, notably brain, spinal cord and muscle. It acts as a receptor for neurotensin, but predominates in regions of the nervous system that neither synthesize nor respond to this neuropeptide, suggesting that sortilin has additional roles. Sortilin is expressed during embryogenesis in areas where nerve growth factor (NGF) and its precursor, proNGF, have well-characterized effects. These neurotrophins can be released by neuronal tissues, and they regulate neuronal development through cell survival and cell death signalling. NGF regulates cell survival and cell death via binding to two different receptors, TrkA and p75NTR (ref. 10). In contrast, proNGF selectively induces apoptosis through p75NTR but not TrkA. However, not all p75NTR-expressing cells respond to proNGF, suggesting that additional membrane proteins are required for the induction of cell death. Here we report that proNGF creates a signalling complex by simultaneously binding to p75NTR and sortilin. Thus sortilin acts as a co-receptor and molecular switch governing the p75NTR-mediated pro-apoptotic signal induced by proNGF.     

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.     

Autophagy in thymic epithelium shapes the T-cell repertoire and is essential for tolerance

Recognition of self-antigen-derived epitopes presented by major histocompatibility complex class II (MHC II) molecules on thymic epithelial cells (TECs) is critical for the generation of a functional and self-tolerant CD4 T-cell repertoire. Whereas haematopoietic antigen-presenting cells generate MHC-II-peptide complexes predominantly through the processing of endocytosed polypeptides, it remains unknown if and how TECs use unconventional pathways of antigen presentation. Here we address the role of macroautophagy, a process that has recently been shown to allow for endogenous MHC II loading, in T-cell repertoire selection in the mouse thymus. In contrast to most other tissues, TECs had a high constitutive level of autophagy. Genetic interference with autophagy specifically in TECs led to altered selection of certain MHC-II-restricted T-cell specificities and resulted in severe colitis and multi-organ inflammation. Our findings indicate that autophagy focuses the MHC-II-peptide repertoire of TECs on their intracellular milieu, which notably comprises a wide array of otherwise strictly 'tissue-specific' self antigens. In doing so, it contributes to T-cell selection and is essential for the generation of a self-tolerant T-cell repertoire.     

An Arabidopsis hAT-like transposase is essential for plant development

A significant proportion of the genomes of higher plants and vertebrates consists of transposable elements and their derivatives. Autonomous DNA type transposons encode a transposase that enables them to mobilize to a new chromosomal position in the host genome by a cut-and-paste mechanism. As this is potentially mutagenic, the host limits transposition through epigenetic gene silencing and heterochromatin formation. Here we show that a transposase from Arabidopsis thaliana that we named DAYSLEEPER is essential for normal plant growth; it shares several characteristics with the hAT (hobo, Activator, Tam3) family of transposases. DAYSLEEPER was isolated as a factor binding to a motif (Kubox1) present in the upstream region of the Arabidopsis DNA repair gene Ku70. This motif is also present in the upstream regions of many other plant genes. Plants lacking DAYSLEEPER or strongly overexpressing this gene do not develop in a normal manner. Furthermore, DAYSLEEPER overexpression results in the altered expression of many genes. Our data indicate that transposase-like genes can be essential for plant development and can also regulate global gene expression. Thus, transposases can become domesticated by the host to fulfil important cellular functions.     

Bmi1 is essential for cerebellar development and is overexpressed in human medulloblastomas

Overexpression of the polycomb group gene Bmi1 promotes cell proliferation and induces leukaemia through repression of Cdkn2a (also known as ink4a/Arf) tumour suppressors. Conversely, loss of Bmi1 leads to haematological defects and severe progressive neurological abnormalities in which de-repression of the ink4a/Arf locus is critically implicated. Here, we show that Bmi1 is strongly expressed in proliferating cerebellar precursor cells in mice and humans. Using Bmi1-null mice we demonstrate a crucial role for Bmi1 in clonal expansion of granule cell precursors both in vivo and in vitro. Deregulated proliferation of these progenitor cells, by activation of the sonic hedgehog (Shh) pathway, leads to medulloblastoma development. We also demonstrate linked overexpression of BMI1 and patched (PTCH), suggestive of SHH pathway activation, in a substantial fraction of primary human medulloblastomas. Together with the rapid induction of Bmi1 expression on addition of Shh or on overexpression of the Shh target Gli1 in cerebellar granule cell cultures, these findings implicate BMI1 overexpression as an alternative or additive mechanism in the pathogenesis of medulloblastomas, and highlight a role for Bmi1-containing polycomb complexes in proliferation of cerebellar precursor cells.     

Extra-embryonic function of Rb is essential for embryonic development and viability

The retinoblastoma (Rb) gene was the first tumour suppressor identified. Inactivation of Rb in mice results in unscheduled cell proliferation, apoptosis and widespread developmental defects, leading to embryonic death by day 14.5 (refs 2-4). However, the actual cause of the embryonic lethality has not been fully investigated. Here we show that loss of Rb leads to excessive proliferation of trophoblast cells and a severe disruption of the normal labyrinth architecture in the placenta. This is accompanied by a decrease in vascularization and a reduction in placental transport function. We used two complementary techniques-tetraploid aggregation and conditional knockout strategies-to demonstrate that Rb-deficient embryos supplied with a wild-type placenta can be carried to term, but die soon after birth. Most of the neurological and erythroid abnormalities thought to be responsible for the embryonic lethality of Rb-null animals were virtually absent in rescued Rb-null pups. These findings identify and define a key function of Rb in extra-embryonic cell lineages that is required for embryonic development and viability, and provide a mechanism for the cell autonomous versus non-cell autonomous roles of Rb in development.     

拟南芥bHLH家族转录因子DYT1在花药发育过程中调控胼胝质降解(英文)

胼胝质的合成和降解是雄配子体减数分裂过程中的一个重要特征,对后期花粉成熟有重要作用.在此研究中,分离到了一个雄性不育突变体msl57,该突变体的绒毡层分化及胼胝质降解过程出现异常,导致花粉败育.图位克隆和遗传分析表明:MSl57基因与bHLI-I家族转录因子DYTI(At4g21330)是同一基因.因此,将ms157突变体改名为dyt1-2.反式激活作用实验揭示了DYTI的激活功能域位于基因的250 ～504bp之间.通过酵母双杂交实验发现DYT1蛋白在体内可以形成同源二聚体来执行其功能.RT-PCR及定量PCR分析表明胼胝质酶相关基因A6的表达在突变体背景下严重下调.因此,DVF1通过调控胼胝质的降解来影响花药发育过程.     

Tyrosine phosphatase CD45 is essential for coupling T-cell antigen receptor to the phosphatidyl inositol pathway

Stimulation of T lymphocytes through their antigen receptor (T-cell receptor; TCR) results in the activation of a tyrosine kinase and the generation of phosphatidyl inositol (PtdIns)-derived second messengers. Several reports have indicated that CD45, a haematopoietic cell-specific surface glycoprotein with tyrosine phosphatase activity in its cytoplasmic domain, is important in lymphocyte activation. To examine the possibility that CD45 might influence proximal signal transduction events through the TCR, we have isolated a variant of the human T-cell leukaemic line, HPB-ALL, which fails to express this phosphatase. Unlike cells expressing CD45, stimulation of the TCR in the CD45-negative cell does not result in PtdIns-derived second messengers. Reconstitution of CD45 expression restored early signalling events through the TCR. To localize the site of CD45 action, the human muscarinic type 1 receptor, which also activates the PtdIns second messenger pathway, was transfected into the CD45-negative cell. Although stimulation of the TCR failed to generate PtdIns-derived second messengers, there was normal activity of the PtdIns pathway when human muscarinic receptor type 1 was stimulated, despite the absence of CD45. These data indicate that CD45 influences a cellular component that is essential for effective coupling of the TCR to the PtdIns second messenger pathway.     

Apoptotic cell death induced by c-myc is inhibited by bcl-2.

Apoptosis is a form of physiological cell death, characterized by chromatin condensation, cytoplasmic blebbing and DNA fragmentation, which often depends on RNA and protein synthesis by the dying cell. The c-myc proto-oncogene, usually implicated in cell transformation, differentiation and cell-cycle progression also has a central role in some forms of apoptosis. These opposing roles of myc in cell growth and death require that other gene products dictate the outcome of c-Myc expression on a cell. A candidate for such a modifying gene is bcl-2, whose product prolongs cell survival and blocks apoptosis in some systems. Here we demonstrate that Bcl-2 prevents apoptotic death induced by c-Myc, provide a mechanism whereby cells can express c-Myc without undergoing apoptosis, and give a possible explanation for the ability of Bcl-2 to synergize with c-Myc in cell transformation.     

Two antigen-independent adhesion pathways used by human cytotoxic T-cell clones

Cell-cell adhesion is essential for many immunological functions, including interaction of cytotoxic T lymphocytes (CTLs) with their targets. We have explored CTL-target interactions using well-characterized cloned human CTLs. Conjugate formation between these CTLs and many antigen-negative targets is almost as efficient as with specific target cells, but does not lead to target-cell lysis. Thus, on specific target cells, adhesion by antigen-independent pathways may occur concurrently with or precede antigen recognition. The molecules LFA-1, CD2 (T11, LFA-2) and LFA-3 have been shown to be involved in human CTL conjugation with and lysis of specific target cells. Here we describe monoclonal antibody inhibition studies using individual monoclonal antibodies and mixes which demonstrate (1) that LFA-1, CD2 and LFA-3 are involved in antigen-independent conjugate formation; and (2) suggest that CD2 and LFA-3 are involved in one pathway and LFA-1 in another. We confirmed the existence of distinct pathways by the demonstration that LFA-1-dependent adhesion requires divalent cations and is temperature-sensitive whereas CD2- and LFA-3-dependent adhesion does not require divalent cations and is temperature-insensitive. Together with previous data, our studies suggest that CD2 on the effector interacts with LFA-3 as its ligand on targets.     

工艺创新是现代企业发展的前提

现代企业要在激烈的竞争中赢得市场,就必须以新求胜、以质取胜,必须持续不断地进行技术创新．而工艺创新又是技术创新的基础,是企业发展的前提和动力所在．     

Fibulin-5 is an elastin-binding protein essential for elastic fibre development in vivo.

Extracellular elastic fibres provide mechanical elasticity to tissues and contribute towards the processes of organ remodelling by affecting cell-cell signalling. The formation of elastic fibres requires the assembly and crosslinking of tropoelastin monomers, and organization of the resulting insoluble elastin matrix into functional fibres. The molecules and mechanisms involved in this process are unknown. Fibulin-5 (also known as EVEC/DANCE) is an extracellular matrix protein abundantly expressed in great vessels and cardiac valves during embryogenesis, and in many adult tissues including the aorta, lung, uterus and skin, all of which contain abundant elastic fibres. Here we show that fibulin-5 is a calcium-dependent, elastin-binding protein that localizes to the surface of elastic fibres in vivo. fibulin-5-/- mice develop marked elastinopathy owing to the disorganization of elastic fibres, with resulting loose skin, vascular abnormalities and emphysematous lung. This phenotype, which resembles the cutis laxa syndrome in humans, reveals a critical function for fibulin-5 as a scaffold protein that organizes and links elastic fibres to cells. This function may be mediated by the RGD motif in fibulin-5, which binds to cell surface integrins, and the Ca2+-binding epidermal growth factor (EGF) repeats, which bind elastin.     

p63 is essential for regenerative proliferation in limb, craniofacial and epithelial development

The p63 gene, a homologue of the tumour-suppressor p53, is highly expressed in the basal or progenitor layers of many epithelial tissues. Here we report that mice homozygous for a disrupted p63 gene have major defects in their limb, craniofacial and epithelial development. p63 is expressed in the ectodermal surfaces of the limb buds, branchial arches and epidermal appendages, which are all sites of reciprocal signalling that direct morphogenetic patterning of the underlying mesoderm. The limb truncations are due to a failure to maintain the apical ectodermal ridge, a stratified epithelium, essential for limb development. The embryonic epidermis of p63-/- mice undergoes an unusual process of non-regenerative differentiation, culminating in a striking absence of all squamous epithelia and their derivatives, including mammary, lacrymal and salivary glands. Taken together, our results indicate that p63 is critical for maintaining the progenitor-cell populations that are necessary to sustain epithelial development and morphogenesis.     

Haematopoietic cell-specific CDM family protein DOCK2 is essential for lymphocyte migration

Cell migration is a fundamental biological process involving membrane polarization and cytoskeletal dynamics, both of which are regulated by Rho family GTPases. Among these molecules, Rac is crucial for generating the actin-rich lamellipodial protrusion, a principal part of the driving force for movement. The CDM family proteins, Caenorhabditis elegans CED-5, human DOCK180 and Drosophila melanogaster Myoblast City (MBC), are implicated to mediate membrane extension by functioning upstream of Rac. Although genetic analysis has shown that CED-5 and Myoblast City are crucial for migration of particular types of cells, physiological relevance of the CDM family proteins in mammals remains unknown. Here we show that DOCK2, a haematopoietic cell-specific CDM family protein, is indispensable for lymphocyte chemotaxis. DOCK2-deficient mice (DOCK2-/-) exhibited migration defects of T and B lymphocytes, but not of monocytes, in response to chemokines, resulting in several abnormalities including T lymphocytopenia, atrophy of lymphoid follicles and loss of marginal-zone B cells. In DOCK2-/- lymphocytes, chemokine-induced Rac activation and actin polymerization were almost totally abolished. Thus, in lymphocyte migration DOCK2 functions as a central regulator that mediates cytoskeletal reorganization through Rac activation.