short lived animal models

Question 1

what are the features of a good model organism?

Answer 1

• a well studied lifecycle

-appropriate for the question being asked

-short life span or age-related biomarkers

-is genome sequenced?

Question 2

pros and cons of invertebrate models

Answer 2

pros
-genetics
-easy to manipulate
-environment controllable
-short lifespans

cons
-post-mitotic (c. elegans and D. Melanogaster)
-relevance to mammalian aging
-short lifespans

Question 3

advantages of yeast (Saccharomyces cerevisiae)?

Answer 3

-unicellular eukaryote
-mostly uncomplicated, short lifespan
-many molecular tools
-cheap to grow
-well-developed system of homologous recombination
-homologues and orthologues with human genome-very high
-easy to perform knockouts on individual genes
-16 chromosomes, approx 6000 genes

Question 4

what is the replicative senescence limit for yeast?

Answer 4

approximately 50 generations

Question 5

what does replicative lifespan measure?

Answer 5

it measures the replicative potential

Question 6

chronological lifespan

Answer 6

-measures survival in a post-mitotic, non-replicating phase

-switch to mitochondrial respiration

-low glucose/starvation conditions

Question 7

aging yeast culture process

Answer 7

the aging yeast cells are stained with propidium iodide staining and are seen going through a stationary phase in the culture to view live and dead cells after a certain amount of days. Then they are viewed on microplate imaging, then ANLYSR program to create survival data into a graph

Question 8

Yeast and Sir2

Answer 8

Sir2 = silent information regulator

-histone deacetylase

-sir 2 removes acetyl tags from the histone proteins that package DNA to coil more tightly. it deacetylates
a DNA region that is prone to spinning off

hyperactivated sir2: causes vulnerable genome regions to coil extra tightly, increased sir2 protects yeast cells from forming extra DNA rings allowing them to remain youthful and divide longer

without sir2 activation: after many divisions, the mother accumulates extra DNA rings. after approx. 20 divisions it will become crippled by buildup and die

Question 9

what was the finding from sir 2 promoting longevity study?

Answer 9

That one extra copy of SIR2 gene increases replicative lifespan in yeast

Question 10

disadvantages of yeast

Answer 10

-single cells

-difficulty in insolating one “age” of yeast

-telomeres have no role in yeast “aging”

-do not have an inflammation process–>makes t hard to model human disorders

Question 11

what did Sydney Brenner do?

Answer 11

he chose C. elegans as a simple organisms for easy studies

Question 12

Caenorhabditis elegans is a ______?

Answer 12

nematode, worm

**nematodes are hermaphrodites they can generate both eggs and sperm and also do sexual repro.

Question 13

Advantages of C. elegans

Answer 13

-short lifespan (3 days from egg to egg laying adult)

-959 cells in adult worm- lineage entirely traced

-powerful genetic tools

-insulin/insulin-like growth factor-1 signaling (IIS) pathway conserved between worms and humans

-many physical and Behavioural traits decline with age

-genetic and small molecule drug screens

-transparent

Question 14

C. elegans signs of aging

Answer 14

-reduced fertility, feeding, movement

-increased cuticular wrinkling (collagen cross-linking)

-increased protein carbonyl, mitochondrial DNA deletions, lipofuscin

Question 15

what is lipofuscin?

Answer 15

compound that auto fluroesces. degradation from the liposome and it accumulates with age.

Question 16

post mitotic tissues are great for studying what two things?

Answer 16

neurodegeneration and sarcopenia

Question 17

Sirtuins aging pathway

Answer 17

-important in replicative lifespans

-scars from budding will tell us how many daughter cells have budded off

-daughter cell replicative lifespan will be affected by their mothers—> progressively shorter l

-SIR2 –> When binding NAD, deacetylase inactivates chromatin and forms nicotinamide and metabolite acetyl-ADP-ribose

-when DNA is packed tightly we increase replicative lifespan, generate less chromosomal circles

Question 18

DAF-2 discovery

Answer 18

-characterization of temperature-sensitive mutations

-requires daf-16 for lifespan extension

-both genes involved Dauer formation

-daf-2 group lived longer compared to wild type in a study

-daf2 is a receptor found on the cell surface that binds to insulin-like ligands

Question 19

Dauer formation

Answer 19

describes the alternative developmental stage of nematode worms where the larvae go into a stasis and can survive harsh conditions

mutagenesis is relatively straightforward screen for the phenotype of interest

Question 20

Daf-2/Daf-16

Answer 20

processes affected:

-resistance to infection

-resistance of the cuticle to environmental damage

-increased resistance to mechanical stress

-resistance to muscle degradation

-clearance of degradation products

Question 21

disadvantages of C. elegans

Answer 21

-post-mitotic

-lack many defined organs/tissues

-only 1 mm in length so biochemistry difficulty

-measuring lifespan, not health span

markers of healthspan: muscle function, atrophy, lipofuscin accumulation

Question 22

Drosophila as a model for aging

-fruit fly, D. melanogaster

Answer 22

-short lifespan
-approx 70 days, 90 days maximum at different temperature

-easy to culture

-powerful genetic/molecular tools

-80% of genes involved in human disease have a D. Melanogaster homolog (20-fold smaller genome than mammals but about the same number of gene families)

Question 23

there are age related decreases in what 4 things in flies?

Answer 23

1. reproduction
2. learning
3. behavior
4. locomotion

Question 24

which fly tissues are equivalent to those in mammals?

Answer 24

heart and kidney

Question 25

early studies on flies
Roscoe Hyde

Answer 25

• increase in lifespan when crossing two inbred strains

-10 degree decrease in temperature doubled lifespan

Question 26

Seymour Benzer and aging flies

Answer 26

-circadian rhythms
-neurodegeneration
-aging research

looked for mutants with altered longevity

Methuselah -mutant gene was a member of GPCR family

Question 27

FOXO and aging

Answer 27

FOXO-4E-BP activity in muscles –> preserved proteostasis and muscle function–> delayed systemic aging

Question 28

what is Daf-16?

Answer 28

DAF-16 is part of the insulin/insulin-like growth factor (IGF-1) signaling pathway and is often referred to as a “forkhead box O” (FOXO) transcription factor. FOXO proteins, including DAF-16, are transcription factors that can activate or repress the expression of specific target genes.

Insulin Signaling: DAF-16 activity is often regulated by the insulin/IGF-1 signaling pathway. When insulin/IGF-1 signaling is low, DAF-16 is translocated to the nucleus, where it can regulate target genes. High insulin/IGF-1 signaling inhibits DAF-16 activity, promoting growth and development.

is found in the cytoplasm–> when phosphorylated it will enter and dephosphorylated it will not enter

Question 29

new uses for yeast, worms and flies

Answer 29

-interactions between pathways

-elucidating pathways involved in age-related diseases

-protein folding

Ability to label and monitor in vivo

Question 30

C. elegans as a model for muscular dystrophy

Answer 30

benefits
-easy, cheap
-short lifespan
-similar muscle structure and has orthologues for most human DGC proteins

similarities to DMD in humans
-they display movement and strength decline, altered gait, shortened lifespan

limitations
-very simple body plan
-nonconventional circulatory system
-unable to regenerate muscles
lack of conventional inflammatory system

-we can study the genetic and molecular mechanisms underlying the condition because C. elegans is easy to genetically manipulate, drug screening can be done, and conservation of disease causing genes is present

Question 31

Neurodegeneration in flies

Answer 31

-fruit flies used as a model for neurodegeneration

-Researchers can introduce specific genetic mutations into fruit flies that are associated with human neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, and amyotrophic lateral sclerosis (ALS).

-Phenotypic: Fruit flies can exhibit symptoms related to neurodegeneration

-drug screening, and genetic interactions

Question 32

zebrafish

Answer 32

average lifespan 36-42 months

max lifespan 66 months

-heat shock protein 70 decreases with age

heat shock factor 1 - increased with age

senescence associated B galactosidase staining = was observed in skin with aging

protein oxidation: increased with age in muscle

spinal curvature: observed with aging

Question 33

pros of zebrafish

Answer 33

-vertebrate
-intact nervous system
-orthologs of human genes
-easier to manipulate genetically than mammals

Question 33

cons of zebrafish

Answer 33

-longer lifespan than C. elegans or drosophila

-gene duplication event

-different respiratory system

-tissues have ability to regenerate

-affected by environment (water, temperature, light)

Question 33

Hydra

Answer 33

-small freshwater cnidarian poly

-low senescence

-high regenerative and budding capabilities

-under the right conditions they can essentially live forever

Question 34

advantages of H. oligactis

Answer 34

-shares more genes with humans than C. elegans or D. melanogaster

Question 35

H. oligactis aging

Answer 35

maintained at 18 degrees: indefinite budding for more than 4 years, but transferred to 10 degrees there was a budding arrest, oogenesis and animals exhausted after 8 weeks

Question 36

Hydra pathways

Answer 36

nonsenescent pathway: all hydra especies escape aging under benign conditions and asexual reproduction

-they switch to sexual reproduction after a temperature decline

nonsense pathway: adult survives and continues asexual reproduction during sexual reproduction. This is seen in H. vulgaris

senescent-like pathway: the adult dies following the sexual reproduction pathway. H. oligactis

why are there two different pathways?

hypothesis: environmental response –> if the lake or pond is desiccating or freezing it will switch to the reproductive pathway, produce eggs that are resistant to environmental insults and then the adults eventually die

Question 37

criteria that support aging research in H. oligactis undergoing sexual differentiation

Answer 37

neurodegeneration in humans–> in h oligactis there is disorganization of apical nervous system and loss of neurons, loss of feeding behavior

loss of adult somatic stem cells –> In H. oligactis there is a dramatic reduction in the number of interstitial somatic stem cells

sarcopenia in humans–> disorganization of actin myofibers, loss of contractility, loss of food transfer to the gastric cavity in H. oligactis

100% mortality within 100 years after sexual maturity–> 100% mortality within 120 days after sexual differentiation in H. oligactis

Question 38

summary

Answer 38

there are pros and cons to short-lived model systems. they provide data to “transfer” to mammalian systems. They are generally easier to manipulate at the genetic level. Readout- change in the maximal lifespan

Question 39

what is ERC?

Answer 39

extrachromosomal rDNA circle

rDNA: 150-200 copies of 9kb repeats, sensitive to recombination