Le, Son Tho et al. (2013) International Worm Meeting "Testing for non-Mendelian assortment of chromosomes in Caenorhabditis."

Le, Son Tho, Kao, Chia-Yi, Wang, John

[International Worm Meeting, 2013]

Eukaryotic genome sizes range over 10,000-fold with a correlation between larger genomes and greater organismal size and complexity. In part, population genetic principles can explain this observation. Smaller organisms typically have larger population sizes which are more efficient at purging weakly deleterious mutations such as transposons and other insertions resulting in smaller genome sizes; larger organisms are the opposite. In contrast to the population genetic predictions, the reverse is observed for the species with known genome sizes within the Elegans group of the Caenorhabditis genus. Gonochoristic (male-female) species have larger genomes than hermaphroditic species despite the former predicted to have larger populations sizes than the latter. Why is this? Interestingly, Mendel's law of random chromosome assortment is violated in C. elegans males that are heterozygous for autosomal chromosomes of differing sizes whereby sons inherit the longer chromosome while the hermaphrodite daughters inherit the shorter chromosome, in a phenomenon which we call skew. Because a single hermaphrodite can start a new population, skew could explain how genomes of hermaphroditic species evolve to be smaller than the ancestral gonochoristic species. For this to be true, skew would be predicted to be a general property of the Caenorhabditis species. To this end, we are testing for the presence of skew in other Caenorhabditis species. We are also interested in understanding the mechanisms underlying skew and have initiated a forward genetic screen for genes that suppress skew.

Felix MA et al. (2002) Hermann, Editeurs des Sciences et des Arts. Paris, France. "Caenorhabditis elegans. Un organisme modele en biologie."

Labouesse M, Segalat L, Felix MA

[Hermann, Editeurs des Sciences et des Arts. Paris, France., 2002]

L'espce Caenorhabditis elegans fut dcrite en 1900 Alger par E. Maupas, qui s'intressait son mode de reproduction hermaphrodite. Plus tard, vers le milieu du vingtime sicle, V. Nigon et ses collaboratuers Lyon tudirent les reorganizations cellulaires accompagnant la fecundation et les premiers clivages. J. Brun isola les preiers mutants morpholgiques.

Castellano-Pozo M et al. (2012) PLoS One "The Caenorhabditis elegans THO complex is required for the mitotic cell cycle and development."

Castellano-Pozo M, Garcia-Muse T, Aguilera A

[PLoS One, 2012]

THO is a conserved eukaryotic complex involved in mRNP biogenesis and RNA export that plays an important role in preventing transcription- and RNA-mediated genome instability in mitosis and meiosis. In mammals THO is essential for embryogenesis, which limits our capacity to analyze the physiological relevance of THO during development and in adult organisms. Using Caenorhabditis elegans as a model system we show that the THO complex is essential for mitotic genome integrity and the developmentally regulated mitotic cell cycles occurring during late postembryonic stages.

Jiang LI et al. (1999) Genes Dev "An HMG1-like protein facilitates Wnt signaling in Caenorhabditis elegans."

Sternberg PW, Jiang LI

[Genes Dev, 1999]

We show that during Caenorhabditis elegans male spicule development, the specification of a glial versus neuronal cell fate in a canonical neurogenic sublineage is dependent on Wnt signaling. Inactivation of a Wnt signaling pathway mediated by the Wnt receptor LIN-17 transforms the SPD sheath cell into its sister, the SPD neuron. We discovered a new mutant, son-1, that displays this same cell fate transformation. The son-1 mutation enhances the phenotypes of reduction-of-function lin-17 mutants in several developmental processes, including vulva development, somatic gonad development, and male tail patterning. son-1 encodes an HMG1/2-like DNA-binding protein and is localized in all cell nuclei through development as revealed by a GFP reporter construct. Disruption of son-1 function by RNA-mediated interference results in the same spicule defect as caused by overexpression of POP-1, a TCF/LEF class HMG protein known to act downstream of the Wnt signaling pathway. Our results provide in vivo evidence for the functional involvement of an HMG1/2-like protein, SON-1, in Wnt signaling. The sequence nonspecific HMG protein SON-1 and the sequence specific HMG protein POP-1 might both act in the Wnt responding cells to regulate gene transcription in opposite directions.

Lo, Yun-Hua et al. (2015) International Worm Meeting "Sex-ratio bias in Caenorhabditis."

Yang, Fang-Jung, Le, Son Tho, Wang, John, Hsu, Jung-Chen, Lo, Yun-Hua, Chang, Tiffany

[International Worm Meeting, 2015]

Most sexual species produce nearly equal sex ratios in their offspring. In nematodes, deviations from equal sex ratios occur in the self-fertile hermaphroditic species, which have evolved independently several times. Hermaphrodites produce predominantly hermaphrodite offspring, while sons are rarely observed, consistent with the high theoretical cost of male offspring in these species. In the genus Caenorhabditis, the three known hermaphroditic species also produce occasional males. When crossing occurs in C. elegans, the female-to-male offspring ratio is ~1:1, like most sexual species. In contrast, a previous study demonstrated that C. briggsae has a female-biased sex ratio (~2:1) possibly caused by competition between male X- versus O-bearing sperm.The female-biased sex ratios in C. briggsae may have evolved because of the probable advantages for fathers who produce more daughters, since a solitary hermaphrodite, but not son, can found a population. Alternatively, other conditions, such as local mate competition, may select for female-biased sex ratios. In the first model, only hermaphroditic species should have female-biased sex ratios, while in the second, female/males species could have female-biased sex ratios. To test these two possibilities, we conducted crossing experiments in the third hermaphroditic species, C. tropicalis, as well as 12 female/male species. We found that C. tropicalis produced an offspring sex ratio of ~1:1. For the female/male species, five exhibited ~1:1 ratios while seven others produced female-biased sex ratios. These results suggest that factors other than (or in addition to) hermaphroditism have selected for the evolution of female-biased sex ratios in this clade.

Nathalie Pujol et al. (2001) Worm Breeder's Gazette "Ver midi IV"

Jonathan Ewbank, Nathalie Pujol

[Worm Breeder's Gazette, 2001]

La quatrieme reunion annuelle des equipes francaises ayant un interet pour C. elegans se tiendra le Vendredi 23 fevrier 2001 a Luminy, Marseille. Contact: pujol@ibdm.univ-mrs.fr ewbank@ciml.univ-mrs.fr

Kamp, J.A. et al. (2017) International Worm Meeting "A role for RNA processing proteins in maintaining genome stability."

Lemmens, B.B., Kamp, J.A., Tijsterman, M., van Schendel, R.

[International Worm Meeting, 2017]

Multiple pathways exist to repair DNA double strand breaks (DSBs), and most of the components of these pathways are conserved across species. Yet, which DSB repair pathway acts to repair a DSB depends on the cellular and genomic context and the type of break, and is highly regulated. While Homologous Recombination (HR) and polymerase Theta-Mediated End Joining (TMEJ) are the major DSB repair routes in the germline, the classical Non-Homologous End Joining (cNHEJ) pathway is the main DSB repair pathway in somatic tissues. To identify and characterise genetic factors involved in NHEJ and its regulation, we performed an unbiased forward genetic screen in nematodes carrying a transgenic NHEJ reporter. We isolated seven bona fide NHEJ mutants, three of these contained mutations in the well-known cNHEJ factors cku-70 and cku-80. The other four mutants carried mutations in genes of the THO ribonucleoprotein complex (thoc-2, thoc-5 and thoc-7) and in pnn-1. Both the THO complex and PNN play a role in RNA processing and are conserved in humans. We found that deficiency of PNN and the THO complex also leads to sensitivity to ionizing radiation in somatic tissues, but not in the germline, which is similar to the response of animals defective in cku-70 and cku-80, and points towards a role for the THO complex and PNN in cNHEJ. Transcriptome analysis by RNA sequencing identified a subset of transcripts to be differentially expressed and/or spliced in THO mutants but cNHEJ factors. To identify the mechanism by which the THO complex influences cNHEJ efficiency, a suppressor screen was performed in a thoc-5 deficient background. We found that mutated smg-1 rescues the NHEJ defect in THO complex mutants, but surprisingly this was independent of SMG-1's well-established role in nonsense-mediated decay. These findings classify the phosphatidylinositol 3-kinase-related kinase SMG-1 as a suppressor of NHEJ. To address the hypothesis that SMG-1 is hyperactive in THO complex deficient backgrounds we are currently performing phosphoproteomic experiments. Interestingly, smg-1 mutants are hypersensitive to ionizing radiation-induced DSBs in the germline, similar to HR and TMEJ mutants. This hypersensitivity could suggest that SMG-1 stimulates repair of germline DSBs via HR or TMEJ. We postulate that SMG-1 regulates the repair of DNA double strand breaks by inhibiting NHEJ and promoting other DSB repair pathways.

Castellano-Pozo M et al. (2012) EMBO Rep "R-loops cause replication impairment and genome instability during meiosis."

Aguilera A, Garcia-Muse T, Castellano-Pozo M

[EMBO Rep, 2012]

R-loops are harmful structures with a negative impact on transcription and recombination during mitosis, but no information exists for meiosis. We used Saccharomyces cerevisiae and Caenorhabditis elegans THO mutants as a tool to determine the consequences of R-loops in meiosis. We found that both S. cerevisiae and C. elegans THO mutants show defective meiosis and an impairment of premeiotic replication as well as DNA-damage accumulation. Importantly, RNase H partially suppressed the replication impairment and the DNA-damage accumulation. We conclude that R-loops can form during meiosis causing replication impairment with deleterious results.

Goldstein P (1987) Cell Biol Int Rep "Multiple synaptonemal complexes (polycomplexes): origin, structure and function."

Goldstein P

[Cell Biol Int Rep, 1987]

Multiple synaptonemal complexes (polycomplexes) (PC) are similar in structure to synaptonemal complexes (SC) and are also highly conserved through evolution. They have been described in over 70 organisms throughout all life forms. The appearance of PCs are restricted to meiotic and germ-line derived tissues and are most commonly present after SC formation. However, in a number of animals and plants, both extra- and intranuclear PCs are present during premeiotic and pre-pachytene stages. The structure and biochemical composition of PCs is similar to SCs that the basic unit is tripartite, consisting of two lateral elements and a central region (in which transverse elements are located), and the dimensions of such structures are equivalent. Stacking of SC subunits, while still maintaining equivalent SC dimensions, creates a problem since the lateral elements (LE) would then be twice as thick in the PC as compared to the SC. Recently, it has been shown that the LE of the SC is actually multistranded, thus the LE of each subunit of the PC is half as thick as its counterpart in the SC.

Fan PC et al. (1985) Southeast Asian J Trop Med Public Health "Experimental infection of subperiodic Brugia malayi in laboratory rats with emphasis on evaluation by four techniques."

Hsu YP, Huang CM, Wu CC, Ho CM, Fan PC

[Southeast Asian J Trop Med Public Health, 1985]

Infective larvae of subperiodic B. malayi from South Kalimantan (Borneo), Indonesia collected from laboratory-raised Ae. togoi mosquitoes after feeding on infected mongolian gerbils (Meriones unguiculatus) were inoculated subcutaneously into the groin areas of 15 SD and 36 LE rats. Blood was examined weekly by membrane filtration and thick smears starting 10 weeks post-infection. Microfilariae were found in 3 SD and 4 LE rats, the mf infection rate of 20% and 11% respectively. The prepatent period was significantly shorter in the SD rats (99-112 days) than those in the LE rats (110-153 days). The patent period was longer in the LE rats (208-703 days) than in the SD rats (236-543 days), and the mf density was similar (17.5 mf/20 c.mm blood against 16 mf/20 c.mm blood). At necropsy, 6 (3 female and 3 male) adult worms were recovered from 3 of 6 SD rats and 12 (9 female and 3 male) adult worms from 4 of 20 LE rats; all worms were found in the testes. The results of xenodiagnostic, histochemical staining and measuring spicules and protuberances, demonstrated clearly the difference between both species of Brugia. All dissected Ar. subalbatus mosquitoes exposed to B. pahangi became infected (100%), but none of those to subperiodic B. malayi were infected (0%). The mf of both species of Brugia in thick films stained with naphthol-AS-TR-phosphate showed that the excretory and anal pores of subperiodic B. malayi mf exhibited acid phosphatase activity and only a little activity was seen in other parts; while B. pahangi mf showed heavy diffuse acid phosphatase activity along the entire length of the body.(ABSTRACT TRUNCATED AT 250 WORDS)