Mutations with sensory ray defect unmask cuticular glycoprotein antigens in Caenorhabditis elegans male tail

C. elegans Apical Extracellular Matrices Shape Epithelia

Apical extracellular matrices (aECMs) coat exposed surfaces of epithelia to shape developing tissues and protect them from environmental insults. Despite their widespread importance for human health, aECMs are poorly understood compared to basal and stromal ECMs. The nematode Caenorhabditis elegans contains a variety of distinct aECMs, some of which share many of the same types of components (lipids, lipoproteins, collagens, zona pellucida domain proteins, chondroitin glycosaminoglycans and proteoglycans) with mammalian aECMs. These aECMs include the eggshell, a glycocalyx-like pre-cuticle, both collagenous and chitin-based cuticles, and other understudied aECMs of internal epithelia. C. elegans allows rapid genetic manipulations and live imaging of fluorescently-tagged aECM components, and is therefore providing new insights into aECM structure, trafficking, assembly, and functions in tissue shaping.

Leveraging the withered tail tip phenotype in C. elegans to identify proteins that influence membrane properties

The properties of cellular membranes are critical for most cellular functions and are influenced by several parameters including phospholipid composition, integral and peripheral membrane proteins, and environmental conditions such as temperature. We previously showed that the C. elegans paqr-2 and iglr-2 mutants have a defect in membrane homeostasis and exhibit several distinct phenotypes, including a characteristic tail tip defect and cold intolerance. In the present study we report that screening for novel mutants with these 2 defects can lead to the identification of genes that are important contributors to membrane properties. In particular we isolated 3 novel alleles of sma-1, the C. elegans homolog of βH spectrin, and 2 novel alleles of dpy-23, which encodes the C. elegans homolog of the AP2 μ subunit. We also show that sma-1 and dpy-23 act on membrane properties in pathways distinct from that of paqr-2 and iglr-2.

The Caenorhabditis elegans bus-2 mutant reveals a new class of O-glycans affecting bacterial resistance

Microbacterium nematophilum causes a deleterious infection of the C. elegans hindgut initiated by adhesion to rectal and anal cuticle. C. elegans bus-2 mutants, which are resistant to M. nematophilum and also to the formation of surface biofilms by Yersinia sp., carry genetic lesions in a putative glycosyltransferase containing conserved domains of core-1 beta1,3-galactosyltransferases. bus-2 is predicted to act in the synthesis of core-1 type O-glycans. This observation implies that the infection requires the presence of host core-1 O-glycoconjugates and is therefore carbohydrate-dependent. Chemical analysis reported here reveals that bus-2 is indeed deficient in core-1 O-glycans. These mutants also exhibit a new subclass of O-glycans whose structures were determined by high performance tandem mass spectrometry; these are highly fucosylated and have a novel core that contains internally linked GlcA. Lectin studies showed that core-1 glycans and this novel class of O-glycans are both expressed in the tissue that is infected in the wild type worms. In worms having the bus-2 genetic background, core-1 glycans are decreased, whereas the novel fucosyl O-glycans are increased in abundance in this region. Expression analysis using a red fluorescent protein marker showed that bus-2 is expressed in the posterior gut, cuticle seam cells, and spermatheca, the first two of which are likely to be involved in secreting the carbohydrate-rich surface coat of the cuticle. Therefore, in the bus-2 background of reduced core-1 O-glycans, the novel fucosyl glycans likely replace or mask remaining core-1 ligands, leading to the resistance phenotype. There are more than 35 Microbacterium species, some of which are pathogenic in man. This study is the first to analyze the biochemistry of adhesion to a host tissue by a Microbacterium species.

Identification of cis-regulatory elements from the C. elegans T-box gene mab-9 reveals a novel role for mab-9 in hypodermal function

We have identified Conserved Non-coding Elements (CNEs) in the regulatory region of Caenorhabditis elegans and Caenorhabditis briggsae mab-9, a T-box gene known to be important for cell fate specification in the developing C. elegans hindgut. Two adjacent CNEs (a region 78 bp in length) are both necessary and sufficient to drive reporter gene expression in posterior hypodermal cells. The failure of a genomic mab-9::gfp construct lacking this region to express in posterior hypodermis correlates with the inability of this construct to completely rescue the mab-9 mutant phenotype. Transgenic males carrying this construct in a mab-9 mutant background exhibit tail abnormalities including morphogenetic defects, altered tail autofluorescence and abnormal lectin-binding properties. Hermaphrodites display reduced susceptibility to the C. elegans pathogen Microbacterium nematophilum. This comparative genomics approach has therefore revealed a previously unknown role for mab-9 in hypodermal function and we suggest that MAB-9 is required for the secretion and/or modification of posterior cuticle.

mab-7 encodes a novel transmembrane protein that orchestrates sensory ray morphogenesis in C. elegans

The tapered sensory rays of the male Caenorhabditis elegans are important for successful male/hermaphrodite copulation. A group of ram (ray morphology abnormal) genes encoding modifying enzymes and transmembrane protein have been reported as key regulators controlling ray morphogenesis. Here we report the characterization of another component essential for this morphogenetic process encoded by mab-7. This gene is active in the hypodermis, structural cells, the body seam and several head neurons. It encodes a novel protein with a hydrophobic region at the N-terminus, an EGF-like motif, an ShKT motif and a long C-terminal tail. All these domains are shown to be critical to MAB-7 activity except the EGF-like domain, which appears to be regulatory and dispensable. MAB-7 is shown to be a type II membrane protein, tethered on the cell surface by the N-terminal transmembrane domain with the remainder of the protein exposed to the extracellular matrix. Since ectopic mab-7 expression in any ray cell or even in touch neurons of non-ray lineage can rescue the mutant phenotype, mab-7 is probably acting non-autonomously. It may facilitate intercellular communication among ray cells to augment normal ray morphogenesis.

Caenorhabditis elegans dpy-14: an essential collagen gene with unique expression profile and physiological roles in early development

We describe the molecular characterisation of Caenorhabditis elegans dpy-14, a gene encoding an essential cuticular collagen annotated as col-59. Expression of dpy-14 starts at the 16 E cell stage, making it the earliest-expressing collagen reported to date. SAGE data and dpy-14 promoter::GFP reporter constructs indicate that the gene is transcribed mainly during embryogenesis, specifically in ciliated neurons and hypoderm. Water permeability assays and lectin staining showed that a mutation in the DPY-14 collagen results in defects in the channels of the amphids, which are a class of ciliated neuron, while the amphids appear morphologically normal by dye filling methods. Behavioural assays showed that the ciliated neurons expressing the gene are functional in dpy-14 mutants. All together, our data suggest that ciliated neurons and their hypodermal support cells collaborate in the transcription and synthesis of DPY-14, which then becomes a component of the amphid channels but not of the amphids proper. Interestingly, seam cells of dpy-14 mutants do not properly fuse to form a syncytium. This novel phenotype due to collagen mutations further stresses that dpy-14 plays a fundamental role in C. elegans physiology, since it is required for the proper development of the hypoderm.

Expression of ram-5 in the structural cell is required for sensory ray morphogenesis in Caenorhabditis elegans male tail

Tissue morphogenesis requires complex cellular interaction and communication. The sensory ray in the Caenorhabditis elegans male tail has a simple cellular make-up and a non-essential function, thus providing an ideal model for studying the mechanisms guiding morphogenesis. We present here the analysis of a novel gene, ram-5, mutations of which are characterized by abnormal lumpy rays in the male tail. Microscopic analysis and behavioral studies revealed that lumpy rays contain operational sensory neurons. However, abnormalities were observed in the hypodermis and structural cells as well as in appositions between these two cell types. Molecular cloning and expression studies revealed that the ram-5 gene encodes a transmembrane protein localized in sensory ray support cells, the structural cells. Expression of ram-5 in these cells is required for normal ray morphogenesis. ram-5-dependent cell-cell communication is implicated in organizing the structural cell and the hypodermis, potentially through adhesion at the structural cell-hypodermal cell border.