Metazoan internal organs are assembled from polarized tubular epithelia that must set aside an apical membrane domain as a lumenal surface. In a global Caenorhabditis elegans tubulogenesis screen, interference with several distinct fatty-acid-biosynthetic enzymes transformed a contiguous central intestinal lumen into multiple ectopic lumens. We show that multiple-lumen formation is caused by apicobasal polarity conversion, and demonstrate that in situ modulation of lipid biosynthesis is sufficient to reversibly switch apical domain identities on growing membranes of single postmitotic cells, shifting lumen positions. Follow-on targeted lipid-biosynthesis pathway screens and functional genetic assays were designed to identify a putative single causative lipid species. They demonstrate that fatty-acid biosynthesis affects polarity via sphingolipid synthesis, and reveal ceramideglucosyltransferases (CGTs) as endpoint biosynthetic enzymes in this pathway. Our findings identify glycosphingolipids (GSLs), CGT products and obligate membrane lipids, as critical determinants of in vivo polarity and suggest they sort new components to the expanding apical membrane.

Epithelial tubes are basic building blocks of complex organs, but their architectural requirements are not well understood. Here we show that erm-1 is a unique C. elegans ortholog of the ERM family of cytoskeleton-membrane linkers, with an essential role in lumen morphogenesis. ERM-1 localizes to the luminal membranes of those tubular organ epithelia which lack stabilization by cuticle. RNA interference (RNAi), a germline deletion, and overexpression of erm-1 cause cystic luminal phenotypes in these epithelia. Confocal and ultrastructural analyses indicate that erm-1 functions directly in apical membrane morphogenesis, rather than in epithelial polarity and junction assembly as has been previously proposed for ERMs. We also show that act-5/cytoplasmic actin and sma-1/beta-H-spectrin are required for lumen formation and functionally interact with erm-1. Our findings suggest that there are common structural constraints on the architecture of diverse organ lumina.

One hallmark of innate immunity apparently conserved from primitive life forms through to humans is the ability of the host to recognize pathogen-associated molecular patterns (PAMPs). Since macrophage pattern recognition receptors are not well defined in Drosophila, we set out to identify such receptors. Our findings reveal that Drosophila macrophages express multiple pattern recognition receptors and that the Drosophila scavenger receptor, dSR-CI, is one such receptor capable of recognizing both gram-negative and gram-positive bacteria, but not yeast. Our data indicate that scavenger receptor bacterial recognition is conserved from insects to humans and may represent one of the most primitive forms of microbial recognition.

SUMMARYMany unicellular tubes such as capillaries form lumens intracellularly, a process that is not well understood. Here we show that the cortical membrane organizer ERM-1 is required to expand the intracellular apical/lumenal membrane and its actin undercoat during single-cell C.elegans excretory canal morphogenesis. We characterize AQP-8, identified in an ERM-1 overexpression (ERM-1[++]) suppressor screen, as a canalicular aquaporin that interacts with ERM-1 in lumen extension in a mercury-sensitive manner, implicating water-channel activity. AQP-8 is transiently recruited to the lumen by ERM-1, co-localizing in peri-lumenal cuffs interspaced along expanding canals. An ERM-1[++]-mediated increase in the number of lumen-associated canaliculi is reversed by AQP-8 depletion. We propose that the ERM-1-AQP-8 interaction propels lumen extension by translumenal flux, suggesting a direct morphogenetic effect of water-channel-regulated fluid pressure.

SUMMARYClathrin coats vesicles in all eukaryotic cells and has a well-defined role in endocytosis, moving molecules away from the plasma membrane. Its function on routes towards the plasma membrane was only recently appreciated and is thought to be limited to basolateral transport. Here, an unbiased RNAi-based tubulogenesis screen identifies a role of clathrin (CHC-1) and its AP-1 adaptor in apical polarity during de novo lumenal membrane biogenesis in the C. elegans intestine. We show that CHC-1/AP-1-mediated polarized transport intersects with a sphingolipid-dependent apical sorting process. Depleting each presumed trafficking component mislocalizes the same set of apical membrane molecules basolaterally, including the polarity regulator PAR-6, and generates ectopic lateral lumens. GFP::CHC-1 and BODIPY-ceramide vesicles associate perinuclearly and assemble asymmetrically at polarized plasma membrane domains in a co-dependent and AP-1-dependent manner. Based on these findings, we propose a trafficking pathway for apical membrane polarity and lumen morphogenesis that implies: (1) a clathrin/AP-1 function on an apically directed transport route; and (2) the convergence of this route with a sphingolipid-dependent apical trafficking path. (Belfiore et al., 2002). The temperature-sensitive strain chc-1(b1025) was maintained at 16°C unless indicated otherwise. RNAi and screensA systematic C. elegans tubulogenesis RNAi screen was designed and carried out as previously described, using animals carrying an erm-1::gfp transgene, outlining the lumens of the intestine, the excretory canal and the gonad (Zhang et al., 2011). RNAi was performed by feeding (Timmons et al., 2001).Standard RNAi conditions (used in the screen) were defined as dsRNA induction by 2 mM IPTG. Mild RNAi conditions were empirically determined for specific genes after testing serial concentrations of IPTG and/or dilutions with mock RNAi bacteria: for chc-1, IPTG was titrated down to 2 nM; for aps-1, RNAi bacteria were diluted 1:10 with mock RNAi bacteria. For double RNAi, equal amounts of RNAi bacteria of two clones were mixed. RNAi initiated after completion of embryogenesis involved placing eggs or larvae on RNAi plates for evaluating the same generation. DsRed feedingchc-1(b1025ts) animals were fed on plates containing DsRed RNAi bacteria for at least 12 hours. The DsRed bacterial feeding strain contains a DsRed plasmid in HT115 bacteria that constitutively produces a faint red color. Phenotype reversalchc-1(b1025ts) mutant hermaphrodites were allowed to lay eggs for 1 hour (at 16°C) and subsequently removed. The plates with eggs were transferred to 22°C for 5 hours, then returned to 16°C. Animals were singled the next day and phenotype development and reversal were observed for 6 days. Lipid labeling and assessment of vesicle associationFor lipid labeling, 150 l E. coli OP50 or HT115 were spiked with 2 l 5 mM labeled lipid stock solutions (NBD-C6-glucosylceramide stock was 100 M), for a feeding period of ~8 hours. The same amounts were used f...

We report here the molecular cloning and chromosomal localization of an additional member of the helix-oop-helix (HLH) family of transcription factors, NSCL. The NSCL gene was identified based on its hybridization to the previously described hemopoietic HLH gene, SCL. Murine NSCL cDNA clones were obtained from a day 11.5 mouse embryo cDNA library. The coding region is 399 base pairs and encodes a predicted protein of 14.8 kDa. The nucleotide sequence shows 71% identity and the amino acid sequence shows 61% identity to murine SCL in the HLH domain. The NSCL protein-coding region terminates six amino acids beyond the second amphipathic helix of the HLH domain. Expression of NSCL was detected in RNA from mouse embryos between 9.5 and 14.5 days postcoitus, with maximum levels of expression at 10.5-12 days. Examination of 12-and 13-day mouse embryos by in situ hybridization revealed expression of NSCL in the developing nervous system. The NSCL gene was mapped to murine chromosome 1. The very restricted pattern of NSCL expression suggests an important role for this HLH protein in neurological development.

A total of 60 consecutive patients with localized Ewing's sarcoma of bone who were entered into the Cooperative Ewing's Sarcoma Study of the German Society of Pediatric Oncology from January 1981 until April 1985 were evaluable for tumor volume at diagnosis. The tumor volume was calculated from plain X-rays and CT scans as ellipsoidal or cylindrical depending on the tumor configuration and presence or absence of a soft tissue component. The 3-year disease-free survival rate according to Kaplan-Meier life table analysis was 78% for tumors with a volume less than 100 ml compared to 17% for tumors greater than or equal to 100 ml volume. These results were independent of the site of the tumor, though larger tumors were primarily located in central and proximal extremity sites. Maximal tumor extension was less precise than tumor volume in predicting prognosis. The ratio of tumor volume to body surface area, body length, or body weight did not increase the ability to separate prognostic groups compared to tumor volume. The better prognosis for patients following radical surgery seems to be in part due to a biased distribution of tumor volumes within local therapy groups, since more patients with smaller tumors had surgery for local control.

In prevailing epithelial polarity models, membrane-based polarity cues (e.g., the partitioning-defective PARs) position apicobasal cellular membrane domains. Intracellular vesicular trafficking expands these domains by sorting apicobasal cargo towards them. How the polarity cues are polarized and how sorting confers long-range vesicle directionality is still unclear. Here, a systems-based approach using two-tiered C. elegans genomics-genetics screens identifies trafficking molecules that are not implicated in apical sorting yet polarize apical membrane and PAR complex components. Live tracking of polarized membrane biogenesis suggests that the biosynthetic-secretory pathway, linked to recycling routes, is asymmetrically oriented towards the apical domain during its biosynthesis, upstream of PARs and independent of polarized target domains. This mode of membrane polarization could offer solutions to questions of current models of polarity and polarized trafficking.