Ahmed S et al. (1998) European Worm Meeting "Two C. elegans mutants with defects in telomere replication"

Hodgkin JA, Ahmed S

[European Worm Meeting, 1998]

The germline is a potentially immortal cell lineage which passes from one generation to the next, indefinitely. In order to define genes necessary for germline immortality, we looked for C. elegans mutants with mortal germlines - germlines which could reproduce for several healthy generations but then became sterile. We identified twenty four sen (germline senescence) mutants that became sterile between generations F4 and F16. Some of these mutants displayed secondary phenotypes which give clues as to how their germlines are being damaged. Two mutants, sen-1 and sen-2, produced end-to-end whole chromosome fusions as they approached sterility, suggesting that they might have defects in telomere replication. Indeed, telomeres of both sen-1 and sen-2 shortened by about 12 base pairs per cell division. These results indicate that progressive telomere shortening causes chromosome fusions and germline senescence in C. elegans. While sen-1 and sen-2 both displayed defects in telomere replication, the sen-2 mutant had an additional defect in DNA repair - it was a mutator and was hypersensitive to X-rays. Thus SEN-2 is required for proper processing of double-strand breaks - both abnormal double-strand breaks caused by X-rays and normal double-strand breaks present at telomeres.

Ahmed S et al. (1997) International C. elegans Meeting "sen-1, A SENESCENCE MUTANT WHICH GENERATES DE NOVO CHROMOSOME TRANSLOCATIONS"

Ahmed S, Hodgkin JA

[International C. elegans Meeting, 1997]

The germline is a potentially immortal cell lineage which passes from one generation to the next, indefinitely. In order to investigate how the germline achieves immortality, we looked for C. elegans mutants that can reproduce for several generations but eventually become sterile (germline senescence). 26 candidate sen mutants were identified in a pilot screen of 400 mutagenized worms, suggesting that a large number of genes may be involved in germline immortality. The onset of sterility ranged from generation F4 to generation F16, depending on the mutant. Several sen mutants displayed secondary phenotypes which give clues as to how their germlines are senscing. One mutant, sen-1, has a late-onset Him (high incidence of males) phenotype - it initially has normal broods without males, but later generations always have reduced brood sizes and many males. If these late-onset males are outcrossed, their F1 progeny are often Him. This dominant Him phenotype mapped to the right end of the X for males from six different sen-1 lineages. The dominant Him phenotype also mapped to the end of an autosome in two cases tested thus far (the left end of IV and the right end of V). This data suggests the presence of X-autosome end-to-end fusions, which are known to confer a dominant Him phenotype (Herman et al. 1982, Genetics 102: 379). Since we found different X-autosome fusions in two sen-1 lineages, it is likely that sen-1 is generating de novo chromosome translocations.

Gonzales, Patrick K et al. (2011) International Worm Meeting "Mitochondrial Fission Protects C. elegans from Amyloid-Beta Toxicity."

Link, Christopher D, Gonzales, Patrick K

[International Worm Meeting, 2011]

Alzheimers disease (AD) is a late-onset age-dependent, neurodegenerative disorder affecting 5.3 million Americans. Current evidence points to amyloid beta (Ab), a peptide derived from the amyloid precursor protein (APP), as playing a central role in AD pathogenesis, but mechanisms of Ab toxicity remain unclear. One possible mechanism of Ab toxicity is mitochondrial dysfunction. Amyloid beta induces mitochondrial dysfunction in many AD model systems. Evidence of abnormal mitochondria morphology is present in AD post mortem brain tissue, APP over-expressing neuroblastoma cells, and our Ab expressing transgenic worm. Mitochondria morphology is controlled by a number of fission and fusion genes. Fission and fusion genes are abnormally expressed upon induction of Ab in neuronal cell lines. In this study, we explored the effect of fission and fusion genes on Ab toxicity in a transgenic Ab (1-42) producing worm. We found increased mitochondrial fragmentation in response to Ab induction. We also report that RNAi knockdown of fission genes drp-1 and fis-1 result in increased toxicity, while RNAi of fusion gene eat-3 protects against Ab toxicity. Our results suggest that mitochondrial fission is a protective mechanism against Ab toxicity. Currently, we are exploring autophagy as a potential mechanism for mitochondrial fissions protection against Ab toxicity.

Wood, Michael L et al. (2011) International Worm Meeting "Transgenic Caenorhabditis elegans expressing Alzheimer's pathway proteins to produce b-amyloid toxicity."

Wood, Michael L, Hart, Anne

[International Worm Meeting, 2011]

Neuronal degeneration in Alzheimer's disease (AD) has been associated with intraneuronal aggregation of b-amyloid (Ab). It has been previously shown that neuronal expression of Ab in Caenorhabditis elegans results in intraneuronal accumulation of the peptide along with phenotypes indicating toxicity including, defects in learning behaviors, chemotaxis deficits and hypersensitivity to serotonin (Link, 2006; Wu et al, 2006). Ab is derived from a much larger precursor protein APP which undergoes two cleavage events in the amyloidogenic pathway. Our aim is to create transgenic C. elegans that generate Ab precursor proteins within their neurons. This should lead to the aggregation of Ab and neurodegeneration. We hope this approach will closely mimic the normal pathway of Ab generation in an invertebrate model.

Yuan Luo et al. (2008) C.elegans Aging, Stress, Pathogenesis, and Heterochrony Meeting "Heat Shock Treatment Reduces Beta Amyloid Toxicity In Vivo By Diminishing Oligomers"

Yanjue Wu, Zhiming Cao, Yuan Luo, William Klein

[C.elegans Aging, Stress, Pathogenesis, and Heterochrony Meeting, 2008]

Heat shock response, mediated by heat shock proteins, is a highly conserved physiological process in multicellular organisms for maintenance of cellular homeostasis. Expression of heat shock factors and subsequent heat shock protein plays a role in protection against proteotoxicity in invertebrate and vertebrate models. Proteotoxicity due to b-amyloid peptide (Ab) oligomerization has been linked to the pathogenesis of Alzheimer''s disease. In a transgenic C. elegans model of AD, intracellular expression of human Ab is associated with elevated oxidative stres, accumulation of Ab aggregation and progressive paralysis behavior. Small heat shock protein HSP16.2 has been reported to co-localize with Ab in the transgenic C. elegans, and its over expression suppressed the paralysis. Heat shock response in C. elegans is a neuronal controlled behavior. Transcription factor HSF-1, which regulates heat shock response by up regulation of heat shock proteins in C. elegans, has been coupled to normal aging and age-related diseases. Recently, it also has been associated with dietary restriction and insulin-like signaling in protection against proteotoxicity. However, the functional link between sHSP and Ab on protection against Ab toxicity remains unknown. Previously, we demonstrated that progressive paralysis induced by expression of human Abin transgenic C. elegans was alleviated by Ab oligomer inhibitors ginkgo biloba extract and its constituents (Wu, et al., J. Neurosci 2006, 26:13102-13). In this study, we apply a protective heat shock treatment (2h, 35C) to Ab C. elegans and reveal a significant decrease of Ab toxicity and Ab oligomers in the transgenic worms. This data is consistent with the view that co-expression of HSP16.2 in Ab C. elegans lessened Ab toxicity in these worms. In addition, it provides new insight into the role of non-invasive physical treatment and endogenous chaperone proteins in regulation of Ab aggregation and toxicity.

Gendreau SB et al. (1994) Dev Biol "The potential to differentiate epidermis is unequally distributed in the AB lineage during early embryonic development in C. elegans."

Gendreau SB, Terns RM, Rothman JH, Moskowitz IPG

[Dev Biol, 1994]

In the early Caenorhabditis elegans embryo most of the ectoderm arises from the AB blastomere, one of the six founder cells. We report that nonequivalent blastomeres are generated at the third division round in the AB lineage. Each AB granddaughter divides to produce one cell that has the potential to make abundant epidermis and one that instead produces primarily nervous system. This unequal distribution of the potential to make epidermis occurs in an AB granddaughter that is isolated by laser-ablation of all other cells or during the development of an isolated AB blastomere in culture. The fidelity of this event is normally masked by a signal from the MS founder cell, which induces mesoderm in particular AB descendants. When MS induction is prevented by laser cell-ablation or by a mutation in the glp-1 gene, the epidermal fate map of the AB great granddaughters becomes left-right symmetrical. Cell lineage analyses demonstrate that, in fact, the AB lineage becomes entirely left-right symmetrical in the absence of MS induction. This accounts for the extra epidermal cells previously observed in a glp-1 mutant. Our results suggest that epidermal differentiation in the nematode may be controlled by a cell-autonomous mechanism that differentially allocates epidermal potential during AB development and that MS induction generates the left-right asymmetry in the fates of AB descendants in part by overriding this potential.

McColl G et al. (2012) Mol Neurodegener "Utility of an improved model of amyloid-beta (A) toxicity in Caenorhabditis elegans for drug screening for Alzheimer's disease."

McColl G, Roberts BR, Cherny RA, Roberts CM, Link CD, Ryan TM, Kenche VB, Pukala TL, Masters CL, Bush AI, Barnham KJ

[Mol Neurodegener, 2012]

BACKGROUND: The definitive indicator of Alzheimer's disease (AD) pathology is the profuse accumulation of amyloid-B (AB) within the brain. Various in vitro and cell-based models have been proposed for high throughput drug screening for potential therapeutic benefit in diseases of protein misfolding. Caenorhabditis elegans offers a convenient in vivo system for examination of AB accumulation and toxicity in a complex multicellular organism. Ease of culturing and a short life cycle make this animal model well suited to rapid screening of candidate compounds. RESULTS: We have generated a new transgenic strain of C. elegans that expresses full length AB. This strain differs from existing AB models that predominantly express amino-truncated AB. The AB is expressed in body wall muscle cells, where it oligomerizes, aggregates and results in severe, and fully penetrant, age progressive-paralysis. The in vivo accumulation of AB also stains positive for amyloid dyes, consistent with in vivo fibril formation. The utility of this model for identification of potential protective compounds was examined using the investigational Alzheimer's therapeutic PBT2, shown to be neuroprotective in mouse models of AD and significantly improve cognition in AD patients. We observed that treatment with PBT2 provided rapid and significant protection against the AB-induced toxicity in C. elegans. CONCLUSION: This C. elegans model of full length AB expression can now be adopted for use in screens to rapidly identify and assist in development of potential therapeutics and to study underlying toxic mechanism(s) of AB.

Schonegg S et al. (2014) Genesis "Timing and mechanism of the initial cue establishing handed leftright asymmetry in Caenorhabditis elegans embryos."

Hyman AA, Schonegg S, Wood WB

[Genesis, 2014]

By the six-cell stage, embryos of Caenorhabditis elegans are morphologically LR asymmetric with an invariant handedness that persists throughout development. We used intracellular markers to ask whether breaking of LR symmetry could be observed at earlier stages. Observation of two- to three-cell embryos carrying intracellular markers indicated that LR symmetry is broken concomitantly with establishment of DV axis polarity during division of the anterior AB cell. The AB cleavage furrow initiates asymmetrically and always from the left, suggesting LR differences in the AB cell cortex. An invariantly handed cortical rotation observed earlier during first cleavage implies that the one-cell embryo has an intrinsic chirality. We propose that LR differences in the cortex could result from mechanical forces on asymmetric components of a chiral cortical network during the off-axis elongation of the AB-cell spindle prior to AB cleavage.

McColl, Gawain et al. (2011) International Worm Meeting "Improved Alzheimer's Disease Model of Ab1-42 toxicity."

Roberts, Christine, McColl, Gawain, Link, Christopher, Bush, Ashley, Gunn, Adam, Pukala, Tara, Roberts, Blaine, Cherny, Robert

[International Worm Meeting, 2011]

One of the hallmarks of Alzheimer's disease is the cerebral deposition of plaques composed of Amyloid-beta (Ab) peptide. Human Ab (e.g. in brain, CFS or plasma) is not found as a single species, but rather as diverse mixtures of various modified and truncated forms. Caenorhabditis elegans offers a simplified in vivo system in which to examine Ab accumulation, including sub-cellular localization, and toxicity. We determined that an earlier model of Ab expression in C. elegans accumulates Ab3-42 due to mis-cleavage of a synthetic signal peptide. To achieve correct signal peptide cleavage we inserted an extra Asp-Ala (DA) N-terminal to the hu-Ab sequence in the transgene construct The molecular identity of the Ab expressed was then determined via complimentary techniques. Using immunocapture and electrospray ionization mass spectrometry (ESI-MS) we determined the mono-isotopic molecular weight of the expressed Ab as 4511.2586 Da with an error of 2.5 ppm. This mass is consistent with full length Ab1-42 (expected mass 4511.2697 Da). The Ab1-42 is expressed in body wall muscle cells, where it aggregates and results in severe, and fully penetrant, age progressive-paralysis. The in vivo accumulation of Ab1-42 also stains positive for amyloid dyes, consistent with in vivo fibril formation. This C. elegans model of full length Ab expression can now be adopted to study underlying toxic mechanism(s) of Ab1-42.

Jensen, Louise et al. (2009) International Worm Meeting "Characterization of novel genes found to accelerate amyloid-beta toxicity in a C. elegans model for Alzheimer's disease."

Olsen, Anders, Jensen, Louise, Swistowski, Andrzej, Jakobsen, Helle, Bredesen, Dale

[International Worm Meeting, 2009]

Alzheimer''s disease (AD) is the most common type of dementia among elderly, but the mechanisms causing AD are still largely unknown. Cerebrovascular deposits of amyloid-beta (Ab) plaques and tau protein tangles have long been considered hallmarks of AD. However, although they are present in the brains of the diseased, it is becoming clear that the deposits themselves may not be toxic. On the contrary, these aggregates may provide a protective mechanism whereby the cell immobilizes toxic species of soluble Ab-oligomers. Ab is generated from cleavage of Ab precursor protein (APP). To understand the biology of APP, binding partners of APP binding protein 1 X11a (APPB1) was identified (Bredesen Lab, unpubl.), 22 of these with good homology to C. elegans proteins. In order to test these APPB1 binding proteins in an in vivo model, we RNAi inactivated these genes in a C. elegans model expressing human Ab42 in muscle, showing an age-related increase in Ab-aggregation and paralysis1. We found that inactivation of three of these genes dramatically alters toxicity in Ab-worms, but not in controls. Paralysis over time was greatly accelerated when these genes were inactivated and for one of the genes this was extremely severe. Interestingly, this gene also seems to play a role in the toxicity of protein aggregation in general, as is the case for several Ab-toxicity modulating genes, e.g. hsf-1 and hsp-70. When we inactivated the gene in a model for Parkinsons disease overexpressing a-synuclein in muscle cells, this lead to an increased formation of vesicles of a-synuclein, as previously reported in this model2. Complementing the RNAi analysis in the Ab-model, Western blots probed with anti-Ab42-antibody revealed large differences in the distribution of Ab-oligomers in RNAi treated animals compared to RNAi controls. We are currently investigating the Ab-distribution further using WB and immunostaining as well as investigating genetic pathways these candidate genes for Ab toxicity may operate in. 1: Link, C.D. 1995. PNAS 92: 9368-9372 2: van Ham, T.J. et al. 2008. PLoS Genet 4: 1-11.