Murakami S et al. (1997) International C. elegans Meeting "daf-23 may not be age-1"

Murakami S, Johnson TE, Kliminskaya M

[International C. elegans Meeting, 1997]

Both age-1 and daf-23 mutants show a life-extension (Age) phenotype under some conditions. age-1 mutants form dauer only at semi-lethal 27 oC, whereas daf-23 mutants are non-conditional dauer formers with a strong maternal effect. Recently, Malone et al., 1996 and Morris et al, 1996 observed that age-1(hx546) fails to complement daf-23 alleles for Daf-c and Age phenotype. They concluded that age-1 and daf-23 are allelic. The latter also found mutation sites in a PI3 kinase gene in daf-23 alleles but not in age-1(hx546). We have sought the location of age-1 mutation sites, because such information could provide an insight into the !healthy! life extension of age-1 mutants and an absebce of the maternal effect. Direct sequencing has been used to determine the mutation sites in four age-1 alleles, hx546, z10, z12, and z25. We have completed sequencing the PI3 kinase gene including the introns in hx546 and z25 and almost completed z10 and z12; no mutation site has been found. This argues against the conclusion that age-1 and daf-23 are the same gene. Thus, we have re-tested the genetic complementation. Though we have obtained similar results to the previous work, we found two separable Daf-c Age mutants in the age-1(hx546) strain (we provisionally call them age-1(L) and age-1(R); see also 1996 West Coast Meeting Abstract 137). Both fail to complement daf-23 mutations. This implicates non-allelic non-complementation between age-1(L), age-1(R) and daf-23. Since only the complementation data suggest age-1/daf-23 allelism, it is not clear that age-1 and daf-23 are the same gene.

Murakami S et al. (1996) West Coast Worm Meeting "ARE AGE-1 AND DAF-23 ALLELIC?"

Murakami S, Johnson TE, Duhon SA, Kliminskaya M

[West Coast Worm Meeting, 1996]

Recently, Malone et al (1996) found that age-1 strains (hx542 and hx546) show a Daf-c phenotype at semi-lethal 27 oC. They also showed that age-1(hx546) fails to complement daf-23 alleles. We found that the age-1(hx546) strains contain two Daf-c mutations close to each other. One Daf-c is mapped between sqt-1 and lin-29, where daf-23 is located; the other is to the left of sqt-1, perhaps consistent with the original map position of age-1. These results are not necessarily contradictory to Malone et al, since they used recombinants from mapping Daf-c in the age-1 strains. We are testing whether either Daf-c is responsible for failure to complement daf-23 and/or for failure to complement new alleles of age-1. Current data will be presented.

Murakami, S. (2011) International Worm Meeting "Clarifying misconceptions about age-related memory impairment (AMI)."

Murakami, S.

[International Worm Meeting, 2011]

Age-related memory impairment (AMI) includes mild impairment of the ability to learn new information and to recall previously learned information. The term, age-associated cognitive impairment (AACI), is also used to describe memory impairment during aging. We define AMI (or AAMI) as memory impairment in comparison with young normal controls (young v.s. old comparison); and AACI as in comparison with age-matched normal counterparts (non-AMI v.s. AMI comparison at the same age) (1). We prefer using AMI over AAMI, since AAMI is often confused with the transition state, MCI. Here we clarify some misconceptions we encountered through scientific communication. Firstly, AMI is not a simple decrease in learning and memory. Recent studies suggest that aging causes not only declines but also increases of learning and memory. AMI is not a gradual decay but rather an aspect of age-related alterations in the nervous functions. Importantly, neural loss plays a minor role in AMI. Secondly, AMI is not a disease. AMI is a normal state prior to the disease state. What distinguishes AMI from dementia besides cognitive deficits? A few lines of evidence analysis in humans suggest that reduced metabolic activity may be a hallmark of AMI in humans. Finally, AMI cannot be independent of aging. There is an argument that aging should be separated from AMI. However, aging affects learning and memory, which results in AMI. More precisely, AMI is caused by age-related processes that affect learning and memory. The age-related processes should include age-related changes in neurons as well as elsewhere, including modifiers and pathways for learning and memory. In fact, a type of AMI can be suppressed by serotonin inhibitors, which are good examples for such modifiers. It is unlikely that aging neurons are the sole cause of AMI. Thus, focusing only on neurons would miss important aspects of the mechanisms for AMI. Although the study of aging neurons has been emphasized, it is equally essential to investigate the aging processes. More details are discussed in Ref. 1. The abstract may be presented with the other presentation. Reference: 1. Murakami, S., Cabana, K., Anderson, D. Current advances in the study of oxidative stress and age-related memory impairment in C. elegans. John Wiley & Sons, Hoboken, NJ. In Press.

Murakami S et al. (1997) International C. elegans Meeting "Anti-aging kinase receptor"

Murakami S, Johnson TE

[International C. elegans Meeting, 1997]

It is probable that the gerontogenes identified in C. elegans negatively regulate life extension and stress resistance. The gerontogenes include age-1, daf-2, daf-23, spe-26 (two alleles show Age), and clk-1 (an allele shows Age). To identify genes antagonistic to these gerontogenes, we have performed a computer similarity search and a genomic screening to find genes that can cause increased stress resistance. We have identified a novel tyrosine kinase receptor gene, designated tkr-1, with a similarity to the mammalian receptor kinases, c-kit, platelet derived growth factor receptor (PDGF-R) and fibroblast growth factor receptor (FGF-R). Over-production of tkr-1 causes increased resistance to UV radiation and heat. The tkr-1 also extends mean life span by up to 60 %; this extension is similar to age-1 mutants. Interestingly, a candidate for a tkr-1 knockout was isolated as a downstream suppressor of age-1. In contrast to previously identified gerontogenes, these data suggest: (1) tkr-1 positively regulates stress resistance and life extension; (2) tkr-1 may act downstream of age-1.

Murakami S et al. (1996) West Coast Worm Meeting "LIFE-EXTENSION PATHWAY IN C.ELEGANS"

Johnson TE, Dames SA, Murakami S, Tedesco PM, Duhon SA

[West Coast Worm Meeting, 1996]

Life extension is conferred either by mutants extending adult life (Age), including age-1, daf-2, daf-23, daf-28, spe-26, and an allele of clk-1. Another mode of life extension is conferred by mutants delaying developmental stage (Clk), including clk-1, clk-2, clk-3, gro-1(Wong et al., 1995; Lakowski and Hekimi, 1996). Three groups have identified a life-extension pathway formed by some Daf mutations (Dorman et al., 1995; Larsen et al., 1995; Murakami and Johnson, 1996). We found that the pathway is not limited to Daf mutations but includes other types of the Age mutants (Murakami and Johnson, 1996). Interestingly, the pathway confers UV resistance, suggesting that UV resistance is a good indicator of Age. It is also consistent with the hypothesis that stress resistance is a rate limiting factor determining longevity. We are also testing whether the Age-pathway can confer other types of stress such as H2O2 and heat.

Murakami S et al. (1995) International C. elegans Meeting "LONGER-LIFE MUTANTS SHARE A COMMON MECHANISM CONFERRING RESISTANCE IN C.ELEGANS"

Johnson TE, Murakami S

[International C. elegans Meeting, 1995]

Several single-gene mutations confer longer life (Age). Disparate mechanisms (reduced fertility, turn on of a dauer program, and increased stress resistance) have been proposed to function in spe-26, daf-2, and age-1, respectively. We have found a phenotype common to all available Age mutants: increased UV resistance in adult hermaphrodites. In all cases, the increased UV resistance phenotype was suppressed by daf-16(m26), which also suppressed the Age phenotype of all three mutants: daf-16 did not suppress the reduced fertility of spe-26, nor is there any detectable induction of dauer formation by age-1 or spe-26. These results suggest two conclusions: 1) longer life in all three seemingly disparate share a common genetic pathway; 2) the life-extension mechanism involves UV resistance. Note we think it hard to rule out non-specific suppression of life extension and UV resistance by other dauer-defective mutants that have life spans shorter than wild type, for example, daf-18. One tempting conclusion is that the Age phenotype of spe-26 does not result from reduced fertility but rather induces a stress resistance pathway.

Murakami, S. et al. (2011) International Worm Meeting "Unexpected antagonistic pleiotropy in the sod-4 extracellular supreoxide dismutase gene in C. elegans."

Lim, D., Murakami, S., Yeh, A., Nia, B.V., Murakami, H.

[International Worm Meeting, 2011]

An important principle of the evolutionary theories of aging is that the force of natural selection diminishes late in life. Based on the principle, two popular theories of aging predict the genes that contribute to aging. The mutation accumulation theory predicts accumulation of the genes (or mutations) with late harmful effects. The antagonistic pleiotropy theory predicts a similar but more focused set of the genes that have early beneficial effects at the cost of late harmful effects (referred to as pleiotropic genes). Although the theories may result in different age-related genetic equilibriums, pleiotropic genes are more or less covered in both of the theories. Pleiotropic genes have been found as a form of mutations or gene inactivation with increased lifespan, which show early deficits in development and reproduction. However, mutations that cause damage early in life are problematic to test, as early damage may affect lifespan. In addition, the genes, which are protective against intrinsic and environmental stress, were not thought to be pleiotropic genes, since they are beneficial throughout lifespan. Here we show that the sod-4 gene, a gene protective against oxidative stress, is a new type of pleiotropic genes. Using genetic screening combined with in vivo imaging analysis for reactive oxygen species (ROS), we have identified the sod-4 mutation. The sod-4 gene is the only C. elegans gene for extracellular superoxide dismutase (EC-SOD), which can scavenge deleterious reactive oxygen species (ROS). Mutations in sod-4 caused embryonic lethality, delayed development and reduced fertility. Surprisingly, the sod-4 mutant showed increased fitness during adult phase. The results suggest an unusual example of pleiotropy, which is antagonistic early and late in life. Since recent results questioned the role of age-related oxidative stress in aging, this study offers a first step for more detailed understanding of oxidative stress and aging. Another theory of aging ("midlife crisis" theory) is consistent with the finding, which is being discussed elsewhere.

S Murakami et al. (1999) International C. elegans Meeting "The tkr-1 life-extension gene, which responds to starvation and environmental stress, is regulated by the daf-16 forkhead transcription factor."

S Murakami, TE Johnson

[International C. elegans Meeting, 1999]

Gerontogenes are genes whose alteration causes life extension. Previous studies have identified several C. elegans gerontogenes, including age-1 (phosphatidylinositol 3 OH kinase) and daf-2 (insulin-like receptor), which are negative regulators of longevity and resistance to environmental stress. age-1 and daf-2 have been suggested to form an insulin-like signal transduction pathway dependent on daf-16 (forkhead transcription factor). We have identified a new class of gerontogenes that extend life span when up-regulated. The first such gerontogene was designated tkr-1 (tyrosine kinase receptor-1) (Murakami and Johnson, 1998). Overexpression of tkr-1 extends life span 40-100% and confers increased resistance to heat and UV stress. Purified TKR-1 has tyrosine kinase activity. Mutagenesis analysis suggests that the TKR-1 kinase activity is essential for increased longevity and stress resistance. The cytoplasmic tkr-1 kinase domain shows similarity to the mammalian fibroblast growth factor receptors (FGFR) and can be functionally substituted with that of human FGFR-1. Inactivation of tkr-1 by RNAi and by dominant negative mutations caused developmental delay, decreased reproduction, short life and stress sensitivity. These data strongly indicate that tkr-1 regulates longevity and stress resistance. The overexpression phenotypes of tkr-1 require daf-16 function, suggesting that tkr-1 signaling interlocks with the insulin-like age-1/daf-2 signal transduction pathway. Moreover, TKR-1::GFP analysis suggests that tkr-1 is induced after exposure to UV light, heat, starvation and perhaps oxidative stress. This induction and the expression of tkr-1 during aging is suppressed by a reduction of function mutation in daf-16. In conclusion, tkr-1 is a stress responsive RTK that also regulates longevity and is likely to take part in a daf-16 dependent signal transduction pathway in a way distinct to that of age-1 and daf-2.

Hana Murakami et al. (2007) International Worm Meeting "Behavioral aging and lifespan modulated by serotonin receptors."

Hana Murakami, Karalee Bessinger, Shin Murakami, Gregory Luerman, Jason Hellmann

[International Worm Meeting, 2007]

The neurotransmitter serotonin (5HT) has been implicated to affect variation of longevity in natural Drosophila populations and age-related diseases in mammals. Based on the observations, it has been predicted that serotonin signal, perhaps at levels of serotonin biosynthesis, may control lifespan. Despite the prediction, we found that mutations in the serotonin biosynthesis genes had little or modest effects on life span. Interestingly, a deletion mutation of the ser-1 serotonin receptor gene increased longevity by up to 46%, while a deletion mutation of another serotonin receptor gene, ser-4, shortened early to mid lifespan [1]. The serotonin receptor genes modulate early phase of behavioral aging (locomotion, learning behavior, sensory behavior, etc.) [2; Murakami et al., unpublished] and in stress responses [3] in a different manner. The results provide several important suggestions: (a) Sarcopenia (i.e., muscle frailty) is not the only cause of behavioral aging. (b) Behavioral aging has early and late phases. Early phase occurs prior to the timing when sarcopenia is observed. Serotonin signal modulates early phase. Alterations in neurotransmitters may cause early phase of aging (or post-developmental changes in behaviors) [4]. (c) Late phase is associated with increased oxidative stress in neurons. We are currently defining the roles of oxidative stress in aging of behaviors. References: [1] Murakami H, Murakami S. (2007) Serotonin receptors antagonistically modulate C. elegans longevity. Aging Cell. In Press. [2] Murakami H, Bessinger K, Hellmann J, Murakami S. (2007) Manipulation of serotonin signal suppresses early phase of behavioral aging in Caenorhabditis elegans. Neurobiology of Aging. In Press. [3] Liang B, Moussaif M, Kuan CJ, Gargus JJ, Sze JY. (2006) Serotonin targets the DAF-16/FOXO signaling pathway to modulate stress responses. Cell Metab. 4:429-40. [4] Murakami S. (2007) C. elegans as a model system to study aging of learning and memory. Molecular Neurobiology. In Press.

Pinan-Lucarre, Berangere et al. (2009) International Worm Meeting "Transgenic C. elegans expressing the fungal prion protein HET-s as a model for the study of amyloid infectivity and toxicity."

Qiao, Yujie, Saupe, Sven, Pinan-Lucarre, Berangere, Driscoll, Monica

[International Worm Meeting, 2009]

Amyloids are protein fibers rich in beta sheet structure that are associated with numerous neurodegenerative diseases, including Alzheimer disease. Amyloids have two major biological properties. First, they can be infectious--meaning that they can spread the altered amyloid conformation to the same protein or even among proteins of distinct primary sequence (the latter phenomenon is known as cross-polymerization). Infectious amyloids are called prions. Second, amyloids can be toxic, whether they are infectious or not. Both properties have tremendous fundamental and biomedical impact. [Het-s] is a prion of the fungus Podospora anserina involved in a defense cell suicide mechanism named heterokaryon incompatibility, which disables mixing of different strains by somatic fusion, an ubiquitous feature in filamentous fungi. The HET-s protein exists in a soluble state or in an aggregated, prion state named [Het-s]. The [Het-s] prion is not toxic by itself in P. anserina or in yeast. However cell death is rapidly triggered by the lethal interaction between 2 alleles of the het-s locus: het-S (het-"large S") and het-s (het-"small s") when the HET-s protein adopts the prion form. This prion has been extensively characterized and it is the only prion for which tridimensional structure is available to date. The critical point is that in the [Het-s] system, transgenic expression of het-s allows propagating a non-toxic prion while co-expression of het-s and het-S generates toxicity. We constructed strains expressing het-s or the prion domain only het-s(218-289) (the 218-289 fragment of the protein) as GFP fusions under the control of the ubiquitous promoter dpy-30. The fluorescence of pdpy-30het-s::gfp appears to be mainly diffuse in the cytoplasm while it shows strong aggregation in pdpy-30het-s(218-289)::gfp strains. We constructed strains expressing het-s(218-289)::gfp in the touch neurons using mec-4 promoter and observed that the fusion protein is mostly aggregated into a large fiber spanning the cell body and the proximal part of the axon. These aggregates remain to be shown as infectious [Het-s] amyloids. In future experiments, we will aim to generate neuronal toxicity through the co-expression of het-s(218-289) and het-S. This C. elegans model for prion studies, filling a gap between simple fungal systems and highly complex mammalian systems, might allow a better understanding of the molecular and cellular basis of amyloid infectivity and toxicity.