Fringe benefits to carbohydrates

Delta-like 1 and Delta-like 4 differently require their extracellular domains for triggering Notch signaling in mice

Delta-like (Dll) 1 and Dll4 differently function as Notch ligands in a context-dependent manner. As these ligands share structural properties, the molecular basis for their functional difference is poorly understood. Here, we investigated the superiority of Dll4 over Dll1 with respect to induction of T cell development using a domain-swapping approach in mice. The DOS motif, shared by Notch ligands-except Dll4-contributes to enhancing the activity of Dll for signal transduction. The module at the N-terminus of Notch ligand (MNNL) of Dll4 is inherently advantageous over Dll1. Molecular dynamic simulation revealed that the loop structure in MNNL domain of Dll1 contains unique proline residues with limited range of motion. The Dll4 mutant with Dll1-derived proline residues showed reduced activity. These results suggest that the loop structure-present within the MNNL domain-with a wide range of motion ensures the superiority of Dll4 and uniquely contributes to the triggering of Notch signaling.

Fine-tuning of Notch signaling sets the boundary of the organ of Corti and establishes sensory cell fates

The signals that induce the organ of Corti and define its boundaries in the cochlea are poorly understood. We show that two Notch modifiers, Lfng and Mfng, are transiently expressed precisely at the neural boundary of the organ of Corti. Cre-Lox fate mapping shows this region gives rise to inner hair cells and their associated inner phalangeal cells. Mutation of Lfng and Mfng disrupts this boundary, producing unexpected duplications of inner hair cells and inner phalangeal cells. This phenotype is mimicked by other mouse mutants or pharmacological treatments that lower but not abolish Notch signaling. However, strong disruption of Notch signaling causes a very different result, generating many ectopic hair cells at the expense of inner phalangeal cells. Our results show that Notch signaling is finely calibrated in the cochlea to produce precisely tuned levels of signaling that first set the boundary of the organ of Corti and later regulate hair cell development.

DOI:http://dx.doi.org/10.7554/eLife.19921.001

A gain-of-function suppressor screen for genes involved in dorsal-ventral boundary formation in the Drosophila wing

The Drosophila wing primordium is subdivided into a dorsal (D) and a ventral (V) compartment by the activity of the LIM-homeodomain protein Apterous in D cells. Cell interactions between D and V cells induce the activation of Notch at the DV boundary. Notch is required for the maintenance of the compartment boundary and the growth of the wing primordium. Beadex, a gain-of-function allele of dLMO, results in increased levels of dLMO protein, which interferes with the activity of Apterous and results in defects in DV axis formation. We performed a gain-of-function enhancer-promoter (EP) screen to search for suppressors of Beadex when overexpressed in D cells. We identified 53 lines corresponding to 35 genes. Loci encoding for micro-RNAs and proteins involved in chromatin organization, transcriptional control, and vesicle trafficking were characterized in the context of dLMO activity and DV boundary formation. Our results indicate that a gain-of-function genetic screen in a sensitized background, as opposed to classical loss-of-function-based screenings, is a very efficient way to identify redundant genes involved in a developmental process.

Notch signaling as a therapeutic target in cancer: a new approach to the development of cell fate modifying agents

Notch signaling controls cell fate decisions including during development and stem cell renewal and differentiation in many postnatal tissues. Increasing evidence suggests that the Notch signaling network is frequently deregulated in human malignancies and that genetic or pharmacological manipulation of Notch signaling is a novel potential strategy for the treatment of human neoplasms. This review article summarizes the most recent preclinical and clinical evidence linking Notch signaling to cancer, delineates questions that remain unanswered and explores potential biopharmacological strategies to manipulate Notch signaling in vivo.

Protein glycosylation in disease: new insights into the congenital muscular dystrophies

Glycosylation is the most frequent modification of proteins and is important for many ligand-receptor interactions. Recently, defects in protein glycosylation have been linked to several forms of congenital muscular dystrophy that are frequently associated with brain abnormalities. Muscle-eye-brain disease and Walker-Warburg syndrome are caused by mutations in enzymes involved in O-mannosylation, whereas Fukuyama congenital muscular dystrophy and congenital muscular dystrophy type 1C are caused by mutations in genes that encode putative glycosyltransferases. The common factor in these disorders is defective processing and maturation of a protein called alpha-dystroglycan. This is thought to disrupt the link between alpha-dystroglycan and components of the extracellular matrix, and result in muscle disease and, in many cases, a neuronal-migration disorder.

Homogeneous glycopeptides and glycoproteins for biological investigation

Protein glycosylation is widely recognized as a modulator of protein structure, localization, and cell-cell recognition in multicellular systems. Glycoproteins are typically expressed as mixtures of glycoforms, their oligosaccharides being generated by a template-independent biosynthetic process. Investigation of their function has been greatly assisted by sources of homogeneous material. This review summarizes current efforts to obtain homogeneous glycopeptide and glycoprotein materials by a variety of methods that draw from the techniques of recombinant expression, chemical synthesis, enzymatic transformation, and chemoselective ligation. Some of these techniques remove obstacles to glycoprotein synthesis by installing nonnative linkages and other modifications for facilitated assembly. The end purpose of the described approaches is the production of glycosylated materials for experiments relevant to the biological investigation of glycoproteins, although the strategies presented apply to other posttranslational modifications as well.

A novel thioredoxin-like protein encoded by the C. elegans dpy-11 gene is required for body and sensory organ morphogenesis

Sensory ray morphogenesis in C. elegans requires active cellular interaction regulated by multiple genetic activities. We report here the cloning of one of these genes, dpy-11, which encodes a membrane-associated thioredoxin-like protein. The DPY-11 protein is made exclusively in the hypodermis and resides in the cytoplasmic compartment. Whereas the TRX domain of DPY-11 displays a catalytic activity in vitro, mapping of lesions in different mutant alleles and functional analysis of deletion transgenes reveal that both this enzymatic activity and transmembrane topology are essential for determining body shape and ray morphology. Based on the abnormal features in both the expressing and non-expressing ray cells, we propose that the DPY-11 is required in the hypodermis for modification of its substrates. In turn, ray cell interaction and the whole morphogenetic process can be modulated by these substrate molecules.

Fucosylation of Cripto is required for its ability to facilitate nodal signaling

O-linked fucose modification is rare and has been shown to occur almost exclusively within epidermal growth factor (EGF)-like modules. We have found that the EGF-CFC family member human Cripto-1 (CR) is modified with fucose and through a combination of peptide mapping, mass spectrometry, and sequence analysis localized the site of attachment to Thr-88. The identification of a fucose modification on human CR within its EGF-like domain and the presence of a consensus fucosylation site within all EGF-CFC family members suggest that this is a biologically important modification in CR, which functionally distinguishes it from the EGF ligands that bind the type 1 erbB growth factor receptors. A single CR point mutation, Thr-88 --> Ala, results in a form of the protein that is not fucosylated and has substantially weaker activity in cell-based CR/Nodal signaling assays, indicating that fucosylation is functionally important for CR to facilitate Nodal signaling.

The neural recognition molecule L1 is a sialic acid-binding lectin for CD24, which induces promotion and inhibition of neurite outgrowth

Among the recognition molecules that determine a neuron's interaction with other cells, L1 and CD24 have been suggested to cooperate with each other in neurite outgrowth and signal transduction. Here we report that binding of CD24 to L1 depends on alpha2,3-sialic acid on CD24, which determines the CD24 induced and cell type-specific promotion or inhibition of neurite outgrowth. Using knockout mutants, we could show that the CD24-induced effects on neurite outgrowth are mediated via L1, and not GPI-linked CD24, by trans-interaction of L1 with sialylated CD24. This glycoform is excluded together with L1 from raft microdomains, suggesting that molecular compartmentation in the surface membrane could play a role in signal transduction.