Ageing in C. elegans and the IIS Pathway Flashcards
What provides evidence for the genetic component of ageing?
Some organisms, such as Hydra vulgaris and Urticina felina were non-ageing, and that even very similar organisms could have very different maximum lifespans, such as drosophila and Lasius niger ant queens (3 months and 28 years) or humans and chimps (110 and 60 respectively).
What does the understanding that genetic influences ageing allow for?
A classical genetic approach can be taken; isolating mutants with altered ageing rates and identifying the genes involved, so to gain an insight into the biochemical basis.
What four model organisms are used to study ageing?
Mice, drosophila, elegans and yeast.
The most useful and well-studied model organism for ageing is Caenorhabditis elegans.
How does elegans show ageing?
C. elegans shows ageing through increased protein oxidation, mitochondrial DNA deletions, build-up of lipofuscin, reduced feeding, fertility and movement and cuticular wrinkling due to collagen cross linking.
What advantages does elegans have as a model organism?
C. elegans is also a useful model organism in general; being a transparent microbiverous, 1.2mm nematode worm with a mapped 97Mbp genome containing 19,000 genes with many characterised and explained mutant strains available.
Only having a lifespan of 1-2 weeks allows for rapid results in experiments. The worm also has only males (X0) and hermaphrodites (XX). This worm has the added advantage of being very easy to modify using RNA-mediated RNA interference.
What ageing mutants are most useful for study?
It is generally the long lived mutants that are studied for ageing research, as those who are short lived are often just sick in other specific ways that explain little about ageing in the general population.
What makes elegans such a useful ageing model?
When the larva is exposed to harsh conditions at the L2 stage it can transform into a dauer; essentially going into ‘stasis’ in response to nutrient deficient or high temperature environments, or in response to a pheromone indicating an unsustainably high population.
The length of time spent as a dauer has no effect on the lifespan afterwards as the dauers- are ‘non-ageing’. Thus they possess a way to arrest the ageing process.
What is a dauer?
The dauer is a developmentally arrested form that does not eat, having sealed its buccal cavity, instead relying on its stored food granules. They are resistant to stresses, including from ROS, and have reduced movement (though can still move quickly if pressed to).
They will revive themselves when conditions become more favourable, but the dauer stage can only last for a maximum of 70 days.
What is it assumed that long lived elegans mutants possess?
When the C. elegans was first screened for long-lived mutants it was unsurprising that those found were involved in dauer formation, as dauers appear to be able to ‘stop the clock’ in terms of ageing; prolonging that effect is the assumed principle behind the identified mutants.
What was the first identified elegans long lived mutant?
Michael Klass was the first to identify long-lived mutants through a series of mutagenic experiments, but the work was largely disregarded due to disbelief that mutations could double the natural lifespan of an organism.
It was not until Tom Johnson showed that the gene had this effect regardless of calorie restriction and named it age-1 that it was accepted that a 65% increase in lifespan (and 110% increase in maximum lifespan) was solely due to mutation of the gene.
What are the two primary long lived mutants?
Age1 and daf-2.
Cynthia Kenyon discovered the daf-2 (dauer formation 2) gene, which showed doubled lifespan in mutants and affected dauer formation in C. elegans.
How are age-1 and daf-2 classified?
Both of these mutations, age-1 and daf-2, were classed as daf-c genes, as mutating these daf-c (constitutive) genes leads to formation of dauers when the conditions do not call for it, likewise genes can be daf-d (defective) when their mutation leaves the worm unable to form dauers.
What is the nature of the age-1 and daf-2 mutations?
Partial knockouts of daf-c genes (such as the age-1 and daf-2 mutants identified) are responsible for the increased lifespan, as unlike the total knockouts the dauers are not much more prone to form but the metabolic change is continuously effected.
What is the function of age-1 and daf-2? What does this imply?
The purpose of both the age-1 and daf-2 gene products is to inhibit the daf-16 gene product. It is through the inhibition of this inhibition that the longevity of their mutations is created.
Hence daf-16 is a longevity gene, possibly involved in activating the variety of metabolic changes that cause dauers not to age.
How do age-1/daf-2 mutations and daf-16 mutations interact?
Because the effect of age-1 and daf-2 is dependent upon daf-16, their mutation has no effect on daf-16 knockouts. Conversely, overexpression of daf-16 combined with mutation of age-1 and daf-2 can produce long-lived individuals.
