Drosophila Gp150 is required for early ommatidial development through modulation of Notch signaling

Post-mating gene expression of Mexican fruit fly females: disentangling the effects of the male accessory glands

Mating has profound physiological and behavioural consequences for female insects. During copulation, female insects typically receive not only sperm, but a complex ejaculate containing hundreds of proteins and other molecules from male reproductive tissues, primarily the reproductive accessory glands. The post-mating phenotypes affected by male accessory gland (MAG) proteins include egg development, attraction to oviposition hosts, mating, attractiveness, sperm storage, feeding and lifespan. In the Mexican fruit fly, Anastrepha ludens, mating increases egg production and the latency to remating. However, previous studies have not found a clear relationship between injection of MAG products and oviposition or remating inhibition in this species. We used RNA-seq to study gene expression in mated, unmated and MAG-injected females to understand the potential mating- and MAG-regulated genes and pathways in A. ludens. Both mating and MAG-injection regulated transcripts and pathways related to egg development. Other transcripts regulated by mating included those with orthologs predicted to be involved in immune response, musculature and chemosensory perception, whereas those regulated by MAG-injection were predicted to be involved in translational control, sugar regulation, diet detoxification and lifespan determination. These results suggest new phenotypes that may be influenced by seminal fluid molecules in A. ludens. Understanding these influences is critical for developing novel tools to manage A. ludens.

A conserved major facilitator superfamily member orchestrates a subset of O-glycosylation to aid macrophage tissue invasion

Aberrant display of the truncated core1 O-glycan T-antigen is a common feature of human cancer cells that correlates with metastasis. Here we show that T-antigen in Drosophila melanogaster macrophages is involved in their developmentally programmed tissue invasion. Higher macrophage T-antigen levels require an atypical major facilitator superfamily (MFS) member that we named Minerva which enables macrophage dissemination and invasion. We characterize for the first time the T and Tn glycoform O-glycoproteome of the Drosophila melanogaster embryo, and determine that Minerva increases the presence of T-antigen on proteins in pathways previously linked to cancer, most strongly on the sulfhydryl oxidase Qsox1 which we show is required for macrophage tissue entry. Minerva's vertebrate ortholog, MFSD1, rescues the minerva mutant's migration and T-antigen glycosylation defects. We thus identify a key conserved regulator that orchestrates O-glycosylation on a protein subset to activate a program governing migration steps important for both development and cancer metastasis.

Genetic identification of intracellular trafficking regulators involved in notch dependent binary cell fate acquisition following asymmetric cell division

Notch signaling is involved in numerous cellular processes during development and throughout adult life. Although ligands and receptors are largely expressed in the whole organism, activation of Notch receptors only takes place in a subset of cells and/or tissues and is accurately regulated in time and space. Previous studies have demonstrated that endocytosis and recycling of both ligands and/or receptors are essential for this regulation. However, the precise endocytic routes, compartments and regulators involved in the spatio temporal regulation are largely unknown.

In order to identify Notch signaling intracellular trafficking regulators, we have undertaken a tissue-specific dsRNA genetic screen against candidates potentially involved in endocytosis and recycling within the endolysosomal pathway. dsRNA against 418 genes was induced in Drosophila melanogaster sensory organ lineage in which Notch signaling regulates binary cell fate acquisition. Gain- or loss-of Notch signaling phenotypes were observed in adult sensory organs for 113 of them. Furthermore, 26 genes presented a change in the steady state localization of Notch, Sanpodo, a Notch co-factor, and/or Delta in the pupal lineage. In particular, we identified 20 genes with previously unknown function in Drosophila melanogaster intracellular trafficking. Among them, we identified CG2747 and show that it regulates the localization of clathrin adaptor AP-1 complex, a negative regulator of Notch signaling. All together, our results further demonstrate the essential function of intracellular trafficking in regulating Notch signaling-dependent binary cell fate acquisition and constitute an additional step toward the elucidation of the routes followed by Notch receptor and ligands to signal.

Competition between Delta and the Abruptex domain of Notch

Background

Extracellular domains of the Notch family of signalling receptors contain many EGF repeat domains, as do their major ligands. Some EGF repeats are modified by O-fucosylation, and most have no identified role in ligand binding.

Results

Using a binding assay with purified proteins in vitro, it was determined that, in addition to binding to Delta, the ligand binding region of Notch bound to EGF repeats 22–27 of Notch, but not to other EGF repeat regions of Notch. EGF repeats 22–27 of Drosophila Notch overlap the genetically-defined 'Abruptex' region, and competed with Delta for binding to proteins containing the ligand-binding domain. Delta differed from the Abruptex domain in showing markedly enhanced binding at acid pH. Both Delta and the Abruptex region are heavily modified by protein O-fucosylation, but the split mutation of Drosophila Notch, which affects O-fucosylation of EGF repeat 14, did not affect binding of Notch to either Delta or the Abruptex region.

Conclusion

The Abruptex region may serve as a barrier to Notch activation by competing for the ligand-binding domain of Notch.

The extracellular leucine-rich repeat superfamily; a comparative survey and analysis of evolutionary relationships and expression patterns

BACKGROUND

Leucine-rich repeats (LRRs) are highly versatile and evolvable protein-ligand interaction motifs found in a large number of proteins with diverse functions, including innate immunity and nervous system development. Here we catalogue all of the extracellular LRR (eLRR) proteins in worms, flies, mice and humans. We use convergent evidence from several transmembrane-prediction and motif-detection programs, including a customised algorithm, LRRscan, to identify eLRR proteins, and a hierarchical clustering method based on TribeMCL to establish their evolutionary relationships.

RESULTS

This yields a total of 369 proteins (29 in worm, 66 in fly, 135 in mouse and 139 in human), many of them of unknown function. We group eLRR proteins into several classes: those with only LRRs, those that cluster with Toll-like receptors (Tlrs), those with immunoglobulin or fibronectin-type 3 (FN3) domains and those with some other domain. These groups show differential patterns of expansion and diversification across species. Our analyses reveal several clusters of novel genes, including two Elfn genes, encoding transmembrane proteins with eLRRs and an FN3 domain, and six genes encoding transmembrane proteins with eLRRs only (the Elron cluster). Many of these are expressed in discrete patterns in the developing mouse brain, notably in the thalamus and cortex. We have also identified a number of novel fly eLRR proteins with discrete expression in the embryonic nervous system.

CONCLUSION

This study provides the necessary foundation for a systematic analysis of the functions of this class of genes, which are likely to include prominently innate immunity, inflammation and neural development, especially the specification of neuronal connectivity.

O-linked glycan expression during Drosophila development

Mucin-type O-linked glycosylation is an evolutionarily conserved protein modification that is essential for viability in Drosophila melanogaster. However, the exact role of O-glycans and the identity of the crucial apoproteins modified with O-linked N-acetylgalactosamine (O-GalNAc) remain unknown. In an effort to elucidate the O-linked glycans expressed during Drosophila development, we have employed fluorescent confocal microscopy using a battery of lectins and an antibody specific for the GalNAcalpha-Ser/Thr structure (Tn antigen). Confocal microscopy provides high-resolution images of the diversity of glycans expressed in many developing organ systems. In particular, O-glycans are highly expressed on a number of ectodermally derived tissues such as the salivary glands, developing gut, and the tracheal system, suggesting a role for O-glycans in cell polarity and tube formation common to these organs. Additionally, O-glycans are found in the developing nervous system and within subregions of developing tissues known to be active in cell signaling events. This study provides us with temporal and spatial information regarding O-glycan expression as well as a set of reagents for the isolation of glycoproteins from specific developmental stages and organ systems. This information will aid us in identifying the in vivo substrates of the UDP-GalNAc: polypeptide N-acetylgalactosaminyltranferases, in a continuing effort to define the biological role of O-linked glycoproteins during development.

A Novel 43-kDa Protein as a Negative Regulatory Component of Phenoloxidase-induced Melanin Synthesis

The melanization reaction induced by activated phenoloxidase in arthropods is important in the multiple host defense innate immune reactions, leading to the sequestration and killing of invading microorganisms. This reaction ought to be tightly controlled because excessive formation of quinones and systemic hypermelanization are deleterious to the hosts, suggesting that a negative regulator(s) of melanin synthesis may exist in hemolymph. Here, we report the purification and cloning of a cDNA of a novel 43-kDa protein, from the meal-worm Tenebrio molitor, which functions as a melanization-inhibiting protein (MIP). The deduced amino acid sequence of 352 residues has no homology to known sequences in protein data bases. When the concentration of the 43-kDa protein was examined by Western blot analysis in a melanin-induced hemolymph prepared by injection of Candida albicans into T. molitor larvae, the 43-kDa protein specifically decreased in the melanin-induced hemolymph compared with control hemolymph. Recombinant MIP expressed in a baculovirus system had an inhibitory effect on melanin synthesis in vitro. RNA interference using a synthetic 445-mer double-stranded RNA of MIP injected into Tenebrio larvae showed that melanin synthesis was markedly induced. These results suggest that this 43-kDa MIP inhibits the formation of melanin and thus is a modulator of the melanization reaction to prevent the insect from excessive melanin synthesis in places where it should be inappropriate.

LRR-containing receptors regulating plant development and defense

Despite the presence of more than 400 genes that encode receptor-like kinases (RLKs) in the Arabidopsis thaliana genome, very little is known about the range of biological processes that they control, or the mechanisms by which they function. This review focuses on the most recent findings from studies of several leucine-rich-repeat (LRR) class RLKs in A. thaliana, and their implications for our understanding of plant receptor function and signaling. We compare the biological functions of plant and animal LRR-containing receptors, and the potential commonalities in the signaling mechanisms employed.

Glycosylation regulates Notch signalling

Intracellular post-translational modifications such as phosphorylation and ubiquitylation have been well studied for their roles in regulating diverse signalling pathways, but we are only just beginning to understand how differential glycosylation is used to regulate intercellular signalling. Recent studies make clear that extracellular post-translational modifications, in the form of glycosylation, are essential for the Notch signalling pathway, and that differences in the extent of glycosylation are a significant mechanism by which this pathway is regulated.

Scabrous and Gp150 are endosomal proteins that regulate Notch activity

Notch and Delta are required for lateral inhibition during eye development. They prevent a tenfold excess in R8 photoreceptor cell specification. Mutations in two other genes, Scabrous and Gp150, result in more modestly increased R8 specification. Their roles in Notch signaling have been unclear. Both sca and gp150 are required for ectopic Notch activity that occurs in the split mutant. Similar phenotypes showed that sca and gp150 genes act in a common pathway. Gp150 was required for all activities of Sca, including inhibition of Notch activity and association with Notch-expressing cells that occur when Sca is ectopically expressed. Mosaic analysis found that the gp150 and sca genes were required in different cells from one another. Gp150 concentrated Sca protein in late endosomes. A model is proposed in which endosomal Sca and Gp150 promote Notch activation in response to Delta, by regulating acquisition of insensitivity to Delta in a subset of cells.