Scharf, Andrea et al. (2021) International Worm Meeting "Climate Change and Extinction - Lessons from C. elegans Population Dynamics"

Kornfeld, Kerry, Scharf, Andrea

[International Worm Meeting, 2021]

Biodiversity loss is one of the major challenges for the 21st century. Ecosystems suffer from our modern civilization through pollution, agriculture, overexploitation, industrialization, coastal disturbance, landscaping, and ultimately climate change. Humans have a track record of driving species extinct ranging from passenger pigeons over baiji dolphins to western black rhinoceros. In order to preserve biodiversity and minimize extinction, a deep understanding of population dynamics is necessary. To address this challenge, we are using our previously developed experimental platform comprised of a laboratory ecosystem with C. elegans and a complementary computational simulation. With this platform, we can model how overexploitation, habitat loss, and climate change destabilizes populations to extinction. We found that gradual changes in predation rates, habitat sizes, temperature, and food availability have little effect on population dynamics. In contrast, the populations collapsed if the environmental conditions reached a certain threshold (tipping point) and/or several environmental stressors accumulated. For example, C. elegans populations can only resist starvation for extended periods if predations rates are low and the temperature is optimal. We have defined the conditions for population collapse in wild type C. elegans in order to screen wild isolates, mutants, and in silico mutants for stabilizing traits. One future application is to modify the computational simulation to model different nematode species and to predict for example which plant-parasitic nematode populations are stabilized by increasing temperature due to climate change.

Pickett, Christopher L. et al. (2011) International Worm Meeting "Reproduction and Longevity are Positively Correlated in C. elegans."

Kornfeld, Kerry, Pickett, Christopher L.

[International Worm Meeting, 2011]

The relationships between reproduction and aging are important for understanding mechanisms of aging and evaluating evolutionary theories of aging. To investigate the effects of progeny production on reproductive and somatic aging, we conducted longitudinal studies of C. elegans hermaphrodites. For mated animals, progeny production was positively correlated with reproductive and somatic aging, demonstrating that individuals that generated more progeny also reproduced and lived longer than those that generated fewer progeny. These results indicate that progeny production does not accelerate somatic aging. The longitudinal data demonstrated that cumulative progeny production through day 5 is an early-stage biomarker of aging that is a robust predictor of longevity. Furthermore, early progeny production in mated animals was positively correlated with late progeny production indicating that early progeny production does not accelerate reproductive aging. To independently evaluate the relationships between progeny production and aging, we compared self-fertile hermaphrodites that generated relatively few progeny with mated hermaphrodites that generated many progeny. Somatic aging was not significantly different between these groups, confirming that progeny production does not accelerate somatic aging. The disposable soma and antagonistic pleiotropy theories of the evolution of aging suggest the existence of trade-offs between reproduction and longevity. The results reported here address key predictions of these theories and indicate that individual C. elegans hermaphrodites do not display a trade-off between progeny production and longevity. These studies rigorously define relationships between progeny production, reproductive aging, and somatic aging, define new biomarkers of aging, and contribute to the experimental evaluation of prominent evolutionary theories.

Deshmukh, Krupa et al. (2009) International Worm Meeting "Genomic survey for zinc transport proteins and transcriptional regulation of zinc homeostasis in C.elegans."

Kornfeld, Kerry, Deshmukh, Krupa

[International Worm Meeting, 2009]

Zinc is a vital trace element required by all organisms. Extreme levels of dietary zinc lead to disorders including acrodermatitis enteropathica, a severe case of skin inflammation in humans. Organisms have evolved mechanisms to alleviate adverse effects of high and low zinc levels. We use C.elegans as model system to investigate mechanisms of zinc homeostasis by identifying the proteins involved and also by examining transcriptional changes of genes associated with dietary zinc variations. Zinc transport proteins in C. elegans were identified by surveying its genome, for putative members of two key zinc transport protein families, namely Cation Diffusion Facilitator (CDF) and Zrt/Irt-like Protein (ZIP). We identified 14 CDF and 14 ZIP family proteins in C.elegans, which includes novel CDF and ZIP proteins in addition to those reported by previous studies. Putative CDF and ZIP proteins were classified based on protein sequence similarity with orthologs from other eukaryotes. This classification suggests presence of C.elegans ortholog for every human CDF and ZIP family protein. Transcriptional changes associated with dietary zinc variations have not been systematically studied in C.elegans. We examined changes in mRNA level of candidate genes in response to varying levels of dietary zinc. The genes analysed include ttm-1, a member of CDF family and two metallothionein genes (mtl-1 and mtl-2). Metallothioneins in most eukaryotes chelate excess zinc, cadmium and copper. By manipulating dietary zinc levels in fully defined chemical media (C.elegans Maintenance Media [CeMM]), and by using Quantitative Real Time PCR (qPCR) we analysed relative abundance of the gene transcripts . We find that abundance of ttm-1 transcript increases up to 5-fold with 1000-fold increase in dietary zinc. Increased levels of ttm-1 transcripts at high zinc level is consistent with role of CDF genes in reducing excess levels of cytosolic zinc. mRNA levels of mtl-1 and mtl-2 increased up to 100- and 1000-fold respectively with 1000-fold increase in dietary zinc. Metallothionein genes in C.elegans therefore respond to zinc stress similar to that observed in higher eukaryotes. We generated transgenic worms carrying 5''-upstream regions of mtl-1 and mtl-2 fused to GFP. Green fluorescence signal was induced in worms upon zinc supplementation in their diet. Increased levels of mtl-1 and mtl-2 mRNA is therefore due to upregulation of their transcription under high zinc conditions. We are analysing potenitial regulatory elements responsible for zinc mediated induction of metallothionein genes. By microarray analysis we are further examining whole genomic transcriptional profiles of C.elegans under varying conditions of dietary zinc.

Dietrich, Nicholas K. et al. (2013) International Worm Meeting "Identifying Zrt, Irt-like proteins that promote resistance to zinc toxicity in C. elegans."

Dietrich, Nicholas K., Kornfeld, Kerry

[International Worm Meeting, 2013]

Zinc is a trace element that is essential for the structure and function of a wide range of proteins, and disrupted zinc metabolism is implicated in a number of human diseases. Because both zinc deficiency and excess are deleterious, organisms require homeostatic mechanisms to respond to environmental and dietary changes in zinc availability. In biological systems, zinc exists as a divalent cation that cannot passively cross cell membranes. Therefore, transmembrane proteins that transport zinc across the plasma membrane and the membranes of intracellular organelles play a critical role in zinc metabolism. Two families of evolutionarily conserved zinc transporters have been characterized in animals. Cation diffusion facilitator (CDF) proteins reduce the level of cytoplasmic zinc by transport out of cells or into the lumen or intracellular organelles, whereas Zrt, Irt-like proteins (ZIPs) increase the level of cytoplasmic zinc by transport in the opposite direction. C. elegans has been used to study the function of multiple CDF proteins, but C. elegans ZIP proteins have yet to be characterized. We used bioinformatic approaches to identify predicted ZIP proteins encoded by the C. elegans genome. To determine if any of the predicted genes are functional in zinc metabolism, we perfomed RNAi examining sensitivity to supplemental dietary zinc. To increase the sensitivity of the assay, we utilized a cdf-2;ttm-1 double mutant animal that is hypersensitive to supplemental dietary zinc. We analyzed twelve ZIP genes and showed that reducing the level of C14H10.1 promoted resistance to the growth arrest caused by supplemental dietary zinc. C14H10.1 encodes a predicted protein that is homologous to human ZIP13, and loss-of-function mutations in ZIP13 cause spondylocheiro dysplastic Ehlers-Danlos syndrome. This connective tissue disorder is hypothesized to result from vesicular zinc trapping leading to a deficiency of zinc entering the secretory pathway. These studies have begun to identify a function for C14H10.1 in zinc detoxification and may lead to a genetically tractable model of a human disease.

Pickett, Christopher L. et al. (2013) International Worm Meeting "Age-related degeneration of the egg-laying system promotes matricidal hatching in Caenorhabditis elegans."

Pickett, Christopher L., Kornfeld, Kerry

[International Worm Meeting, 2013]

The identification and characterization of age-related degenerative changes is a critical goal because it can elucidate mechanisms of aging biology and contribute to understanding interventions that promote longevity. We have documented a novel, age-related degenerative change in C. elegans hermaphrodites, an important model system for the genetic analysis of longevity. Matricidal hatching-intra-uterine hatching of progeny that causes maternal death-displayed an age-related increase in frequency and affected ~70% of mated, wild-type hermaphrodites. The timing and incidence of matricidal hatching were largely independent of the levels of early and total progeny production and the duration of male exposure. Thus, matricidal hatching appears to reflect intrinsic age-related degeneration of the egg-laying system rather than use-dependent damage accumulation. Consistent with this model, mutations that extend longevity by causing dietary restriction significantly delayed matricidal hatching, indicating age-related degeneration of the egg-laying system is controlled by nutrient availability. To identify the underlying tissue defect, we analyzed serotonin signaling that triggers vulval muscle contractions. Mated hermaphrodites displayed an age-related decline in the ability to lay eggs in response to exogenous serotonin, indicating that vulval muscles and/or a further downstream function that is necessary for egg-laying degenerate in an age-related manner. By characterizing a new, age-related degenerative event displayed by C. elegans hermaphrodites, these studies contribute to understanding a frequent cause of death in mated hermaphrodites and establish a model of age-related reproductive complications that may be relevant to the birthing process in other animals such as humans.

Roh, Hyun Cheol et al. (2009) International Worm Meeting "Analysis of zinc transporters that regulate zinc metabolism of C. elegans."

Roh, Hyun Cheol, Kornfeld, Kerry

[International Worm Meeting, 2009]

Zinc is a trace element essential for many biological processes. As zinc is required for the function of a number of proteins and plays a role in signal transduction, zinc deficiency causes a broad range of defects. Excess zinc can also be deleterious because it causes zinc toxicity by replacing other metals required for protein functions. Thus, it is necessary for organisms to have mechanisms for zinc metabolism to achieve an optimal level of zinc. Zinc metabolism is mediated by various proteins including zinc transporters, zinc-binding proteins and zinc-sensing proteins. Zinc transporters, composed of two families, cation diffusion facilitator (CDF/SLC30) and Zrt-, Irt-like protein (ZIP/SLC39), control the distribution and the levels of zinc in cells by exporting and importing cytoplasmic zinc ions across membranes, respectively. Although many genes in zinc metabolism have been identified, the mechanisms of how the genes coordinate to regulate zinc homeostasis in whole organisms and how they are related to physiological functions are not well understood. We found that C. elegans has 14 putative CDF and 14 ZIP proteins by genome sequence analysis. We have been characterizing zinc transporters in zinc metabolism and physiology. We have examined the expression patterns of zinc transporters, the changes of expression in response to the changes in dietary zinc levels, and the functions of zinc transporters by using loss-of-function genetic approaches. We found that CDF-2 is expressed in the membrane of gut granules, specialized lysosomes in the intestine, and it is induced by zinc and other metal ion supplements. By contrast, CDF-1 and SUR-7, previously identified CDF proteins, do not respond to dietary zinc levels. cdf-2 (lf) mutants were sensitive to excess zinc, but in normal condition, these mutants were similar to N2 in life-span and sensitivity to other stresses such as heat shock and oxidative stress. Based on these results, we hypothesize that CDF-2 transports zinc ions into gut granules, which are the site for excess zinc storage. To address this hypothesis, we are trying to visualize zinc ions by using zinc-specific fluorescent dyes. We are also investigating the mechanism by which CDF-2 is induced by high levels of zinc. Previously, MDT-15, a mediator subunit, was reported to play a role in the transcriptional response of cdf-2. We found that knockdown of mdt-15 disrupts CDF-2 induction in response to high levels of zinc. Using the transgenic animals, we will search for new genes that are responsible for the induction of gene expression in response to high levels of zinc.

Kumar, Sandeep et al. (2013) International Worm Meeting "An ACE inhibitor extends Caenorhabditis elegans life span."

Dietrich, Nicholas, Kumar, Sandeep, Kornfeld, Kerry

[International Worm Meeting, 2013]

Aging is characterized by progressive, degenerative changes in many organ systems. Age-related degeneration of somatic tissues is a major contributor to disability and death. Treatments that delay age-related degeneration of humans are desirable, but no drugs that delay normal human aging are available. To identify drugs that delay age-related degeneration, we used the C. elegans model system to screen for FDA-approved drugs that can extend the adult lifespan of worms. We showed that captopril, an angiotensin converting enzyme (ACE) inhibitor used to treat high blood pressure, extended mean life span significantly. Captopril inhibits the enzyme ACE in humans, and the worm homolog of ACE is encoded by the acn-1 gene. We discovered that reducing the activity of acn-1 extended the mean life span of worms. acn-1 has previously been shown to play a role in larval molting. Combining treatment with captopril and reducing the activity of acn-1 did not have an additive effect on life span extension, indicating that these interventions may affect the same pathway. Captopril treatment and acn-1 RNAi can further extend the life span of many long-lived mutants, including mutants with defects in caloric intake, mitochondrial function, and insulin/IGF-1 signaling. However, captopril treatment and acn-1 RNAi did not extend the life span of daf-16 mutants. Based on these findings, we hypothesize that captopril extends life span by inhibition of the acn-1 gene, and this life span extension requires DAF-16, the target of the insulin/IGF-1 signaling pathway. The ACE pathway has been implicated in life span regulation in rodents, suggesting this may be an evolutionarily conserved system of life span regulation.

Kocsisova, Zuzana et al. (2015) International Worm Meeting "Monitoring S-phase in aging wild type and mutant C. elegans germlines using EdU labeling and a GFP:PCNA transgene."

Kocsisova, Zuzana, Kornfeld, Kerry, Mohammad, Ariz, Schedl, Tim

[International Worm Meeting, 2015]

The success of an organism is rooted in its ability to generate offspring that will survive and reproduce, but this capacity declines with age. Prominently, in C. elegans hermaphrodites, about one-third of adult lifespan is post-reproductive, even when sufficient sperm are provided by male mating (Hughes et al. 2007). Several mutants have been identified that display an extended mated reproductive span, including eat-2(ad1116), daf-2(e1370), am117, am293, and am294. While we have described quantitatively the progeny output of these mutants, the mechanism of reproductive span extension is unclear. We hypothesize that these mutants have delayed aging of the germline. The development and function of larval and young adult germline have been studied extensively, and it is known that Notch signaling maintains a pool of proliferating mitotic germline stem cells into adulthood. It is not established whether the proliferation of germline stem cells declines with age or whether mutations that extend the reproductive span influence such a decline. The proliferative zone can be assayed by DAPI or by REC-8 HIM-3 staining. However, these methods do not distinguish proliferating and quiescent cells. Pulse labeling with EdU has been used to monitor S-phase in the proliferative zone of young animals (Fox et al. 2011), but this technique requires ingestion of EdU-labeled bacteria. A pie-1p::GFP:PCNA transgene has been used to monitor S-phase in embryos (Brauchle, Baumer, and Gonczy 2003; Kisielewska, Lu, and Whitaker 2005). Here we evaluate whether this transgene can also be used as an alternative to EdU to monitor S-phase in the germline, and whether the two methods mark a highly overlapping pool of nuclei.

Kumar, Sandeep et al. (2011) International Worm Meeting "Identification of mutations that delay reproductive or somatic aging of Caenorhabditis elegans."

Kornfeld, Kerry, Huang, Cheng, Kumar, Sandeep, Hughes, Stacie E

[International Worm Meeting, 2011]

Aging is an important feature of animal biology characterized by progressive degenerative changes in a wide range of organs and tissues, including the reproductive system. Genetic studies have begun to identify genes that can influence lifespan, but little is known about genes that might affect aging of specific tissues. To identify genes that are important for controlling these degenerative changes, we used chemical mutagenesis to perform forward genetic screens in Caenorhabditis elegans. Using a screen focused on somatic tissues, mutants were identified that displayed extended periods of pharyngeal pumping, body movement, or survival. One of these mutations is a novel allele of the age-1 gene. age-1 encodes a phosphatidylinositol-3-kinase (PI3K) that functions in the insulin/insulin-like growth factor-1 (IGF-1) signaling pathway. age-1(am88) creates a missense change in the conserved PIK domain and causes dramatic extensions of the pharyngeal pumping and body movement spans, as well as a two-fold extension of the lifespan. By conducting screens focused on reproductive aging in mated hermaphrodites, we identified mutants that displayed increased progeny production late in life. To characterize these mutations, we developed quantitative measurements of age-related morphological changes in the gonad. The am117 mutation delayed age-related declines in progeny production and morphological changes in the gonad. We are currently using whole genome sequencing to identify the gene affected by am117. These studies provide new insights into the genetic regulation of age-related degenerative changes in somatic and reproductive tissues.

Pickett, Christopher L. et al. (2009) International Worm Meeting "Increasing wild type hermaphrodite brood size does not affect life span."

Kornfeld, Kerry, Pickett, Christopher L., Collier, Sara, Armstead, Brinda L.

[International Worm Meeting, 2009]

Aging is characterized by a progressive decline of tissue organization and function that correlates with chronological age. The link between aging, progeny production, and reproductive decline, however, is controversial. Antagonistic pleiotropy was proposed in the 1950s and theorized that extending life span required a reduction in progeny production, and vice versa. Consistent with this theory, loss- or reduction-of-function mutations in insulin signaling, mitochondrial electron transport, or caloric intake extend life span and often reduce progeny production in a number of organisms. However, the effects of increasing progeny production on life span have not been adequately investigated. To address this, we conducted longitudinal studies using C. elegans N2 hermaphrodites mated to N2 males, and we analyzed brood size, reproductive span, fast body movement span, pharyngeal pumping span, and life span. In addition, hermaphrodites were unmated or mated to sterile fer-6(hc6) males-these animals mate but do not transfer viable sperm. The brood sizes and reproductive spans of mated hermaphrodites were nearly double those of unmated or fer-6(nc6) mated hermaphrodites. We also observed that the fast body movement, pharyngeal pumping, and life spans did not significantly differ among unmated hermaphrodites or those mated to N2 males or fer-6(hc6) males. These data suggest that doubling brood size and extending the reproductive period does not decrease life span, contrary to the predictions of antagonistic pleiotropy. Additionally, our preliminary data suggest that different E. coli strains can increase cross brood size. Animals grown on HT115 have larger cross brood sizes than those grown on OP50. We draw two conclusions from these data. First, animals grown on OP50 are not maximizing their reproductive potential. Second, brood size and life span are not involved in a trade-off in hermaphrodites grown on food that does not maximize their reproductive potential. We are currently testing other bacterial strains and species to determine the maximal level of cross progeny production and the effect on life span. Furthermore, in order to analyze reproduction and life span in C. elegans populations, we are validating a liquid culture system where we control food, predation, and the environment.