Cotranslational endoplasmic reticulum assembly of FcɛRI controls the formation of functional IgE-binding receptors

The human high affinity receptor for IgE (FcɛRI) is a cell surface structure critical for the pathology of allergic reactions. Human FcɛRI is expressed as a tetramer (αβγ2) on basophils or mast cells and as trimeric (αγ2) complex on antigen-presenting cells. Expression of the human α subunit can be down-regulated by a splice variant of FcɛRIβ (βvar). We demonstrate that FcɛRIα is the core subunit with which the other subunits assemble strictly cotranslationally. In addition to αβγ2 and αγ2, we demonstrate the presence of αβ and αβvarγ2 complexes that are stable in the detergent Brij 96. The role of individual FcɛRI subunits for the formation of functional, immunoglobulin E–binding FcɛRI complexes during endoplasmic reticulum (ER) assembly can be defined as follows: β and γ support ER insertion, signal peptide cleavage and proper N-glycosylation of α, whereas βvar allows accumulation of α protein backbone. We show that assembly of FcɛRI in the ER is a key step for the regulation of surface expression of FcɛRI. The ER quality control system thus regulates the quantity of functional FcɛRI, which in turn controls onset and persistence of allergic reactions

Anti-CD63 antibodies suppress IgE-dependent allergic reactions in vitro and in vivo

High-affinity IgE receptor (FcɛRI) cross-linking on mast cells (MCs) induces secretion of preformed allergy mediators (degranulation) and synthesis of lipid mediators and cytokines. Degranulation produces many symptoms of immediate-type allergic reactions and is modulated by adhesion to surfaces coated with specific extracellular matrix (ECM) proteins. The signals involved in this modulation are mostly unknown and their contribution to allergic reactions in vivo is unclear. Here we report the generation of monoclonal antibodies that potently suppress FcɛRI-induced degranulation, but not leukotriene synthesis. We identified the antibody target as the tetraspanin CD63. Tetraspanins are membrane molecules that form multimolecular complexes with a broad array of molecules including ECM protein-binding β integrins. We found that anti-CD63 inhibits MC adhesion to fibronectin and vitronectin. Furthermore, anti-CD63 inhibits FcɛRI-mediated degranulation in cells adherent to those ECM proteins but not in nonadherent cells. Thus the inhibition of degranulation by anti-CD63 correlates with its effect on adhesion. In support of a mechanistic linkage between the two types of inhibition, anti-CD63 had no effect on FcɛRI-induced global tyrosine phosphorylation and calcium mobilization but impaired the Gab2–PI3K pathway that is known to be essential for both degranulation and adhesion. Finally, we showed that these antibodies inhibited FcɛRI-mediated allergic reactions in vivo. These properties raise the possibility that anti-CD63 could be used as therapeutic agents in MC-dependent diseases

Repression of Floral Meristem Fate Is Crucial in Shaping Tomato Inflorescence

Tomato is an important crop and hence there is a great interest in understanding the genetic basis of its flowering. Several genes have been identified by mutations and we constructed a set of novel double mutants to understand how these genes interact to shape the inflorescence. It was previously suggested that the branching of the tomato inflorescence depends on the gradual transition from inflorescence meristem (IM) to flower meristem (FM): the extension of this time window allows IM to branch, as seen in the compound inflorescence (s) and falsiflora (fa) mutants that are impaired in FM maturation. We report here that JOINTLESS (J), which encodes a MADS-box protein of the same clade than SHORT VEGETATIVE PHASE (SVP) and AGAMOUS LIKE 24 (AGL24) in Arabidopsis, interferes with this timing and delays FM maturation, therefore promoting IM fate. This was inferred from the fact that j mutation suppresses the high branching inflorescence phenotype of s and fa mutants and was further supported by the expression pattern of J, which is expressed more strongly in IM than in FM. Most interestingly, FA - the orthologue of the Arabidopsis LEAFY (LFY) gene - shows the complementary expression pattern and is more active in FM than in IM. Loss of J function causes premature termination of flower formation in the inflorescence and its reversion to a vegetative program. This phenotype is enhanced in the absence of systemic florigenic protein, encoded by the SINGLE FLOWER TRUSS (SFT) gene, the tomato orthologue of FLOWERING LOCUS T (FT). These results suggest that the formation of an inflorescence in tomato requires the interaction of J and a target of SFT in the meristem, for repressing FA activity and FM fate in the IM

Transition to Flowering and Morphogenesis of Reproductive Structures in Tomato

Flowering in tomato (Solanum lycopersicum L.) has long been investigated by plant physiologists and horticulturists aiming to increase productivity of this important fruit crop. The disruption of the sequence of events which give rise to normal evelopment of the reproductive structures by either the manipulation of the environment, hormones or mutations has provided information useful to unravel the complexity of the implicated mechanisms. In this paper, we focus on the early stages of the flowering process, analysing how flowering time and reproductive morphogenesis are regulated. Development of the reproductive structures up to anthesis, having been reviewed on several occasions in the past, is not considered. Tomato is an autonomously flowering plant with a sympodial growth habit, which means that it flowers repeatedly, at the top of an initial segment and of successive sympodial segments. The nature of its reproductive structure, a raceme or a cyme, is still questioned but available evidence supports the view that the tomato inflorescence is racemose. Flowering time is strongly dependent on the daily light energy integral and is regulated by an array of genes among which SINGLE FLOWER TRUSS (SFT) and SELF PRUNING (SP) play a major role. SFT is a flowering promoter particularly active in the initial segment while SP regulates sympodial development by controlling the regularity of the vegetative-reproductive switch of the different sympodial segments. Many genes specifying the identity of the meristems and floral organs interact to regulate the morphogenesis of the reproductive structures, opening a large field for future investigations

Reproductive Development in Lolium temulentum L.: Spike Morphogenesis and Grain Set Limitations

Reproductive development in cereals is not easy to investigate because their quantitative response to environmental factors makes it difficult to synchronize the plants. In this paper, one of our aims was to assess whether Lolium temulentum strain Ceres, a qualitative long-day grass, could serve as a model of reproductive development for cereals. The morphological patterns from floral transition to seed set were studied.FRFC n°2.9009.8