SummaryPAR-3 is required for epithelial cell polarity in the distal spermatheca of C. elegans

The par genes of Caenorhabditis elegans are essential for establishment and maintenance of early embryo polarity and their homologs in other organisms are crucial polarity regulators in diverse cell types. Forward genetic screens and simple RNAi depletion screens have identified additional conserved regulators of polarity in C. elegans; genes with redundant functions, however, will be missed by these approaches. To identify such genes, we have performed a genome-wide RNAi screen for enhancers of lethality in conditional par-1 and par-4 mutants. We have identified 18 genes for which depletion is synthetically lethal with par-1 or par-4, or both, but produces little embryo lethality in wild type. Fifteen of the 18 genes identified in our screen are not previously known to function in C. elegans embryo polarity and 11 of them also increase lethality in a par-2 mutant. Among the strongest synthetic lethal genes, polarity defects are more apparent in par-2 early embryos than in par-1 or par-4, except for strd-1(RNAi), which enhances early polarity phenotypes in all three mutants. One strong enhancer of par-1 and par-2 lethality, F25B5.2, corresponds to nop-1, a regulator of actomyosin contractility for which the molecular identity was previously unknown. Other putative polarity enhancers identified in our screen encode cytoskeletal and membrane proteins, kinases, chaperones, and sumoylation and deubiquitylation proteins. Further studies of these genes should give mechanistic insight into pathways regulating establishment and maintenance of cell polarity.T HE regulation of cell polarity is essential for development and function of diverse cell types. The six par genes, first identified for their role in regulating polarity in the one-cell Caenorhabditis elegans embryo (Kemphues et al. 1988;Watts et al. 1996;Morton et al. 2002) are central to the coordinated organization of polarity in a variety of cell types, including epithelial tissues, migrating cells, neurons, and oocytes (reviewed in St Johnston and Ahringer 2010; Nance and Zallen 2011). In the C. elegans zygote, the par genes are required for segregation of cytoplasmic components including developmental determinants and cell timing regulators. Because of the high degree of conservation of the PAR proteins and their partners, C. elegans remains an excellent system for identifying key regulators of polarity.The genes par-1 and par-4 encode conserved serinethreonine kinases. PAR-1 is related to mammalian MARK kinases; PAR-4 is the C. elegans homolog of LKB1, the upstream regulatory kinase of the AMPK kinase family, including MARKs (reviewed by Alessi et al. 2006). LKB1 is a known tumor suppressor for which mutations lead to Peutz-Jegher syndrome and predisposition to cancer in epithelial tissues such as the intestine (Hemminki et al. 1998;Jenne et al. 1998). In the C. elegans embryo, PAR-1 and PAR-4 are essential for asymmetric localization of P granules and developmental regulators such as MEX-5 and PIE-1 and for asynchronous cell divisions of the early b...

Caenorhabditis has proven to be a useful model for studying host-pathogen interactions as well as the ability of nematodes to serve as vectors for the dispersal of foodborne pathogens. In this study, we evaluated whether C. elegans can serve as a host for Listeria spp. While there was an effect of growth media on C. elegans killing, C. elegans exposed to L. monocytogenes and L. innocua pregrown in Luria-Bertani medium showed reduced survival when compared to nonpathogenic E. coli OP50, while L. seeligeri showed survival similar to E. coli OP50. In a preference assay, C. elegans preferred E. coli over L. monocytogenes and L. innocua, but showed no preference between L. monocytogenes and L. innocua. A gentamicin assay indicated that L. monocytogenes did not persist within the C. elegans intestinal tract. Our findings that L. monocytogenes and L. innocua strains tested have equally deleterious effects on C. elegans and that L. monocytogenes did not establish intestinal infection conflict with other recently published results, which found intestinal infection and killing of C. elegans by L. monocytogenes. Further studies are thus needed to clarify the interactions between L. monocytogenes and C. elegans, including effects of environmental conditions and strain differences on killing and intestinal infection.