Previously

Cells need external signals to promote cell proliferation

Cells have internal controls to limit # of divisions

Telomere length as hypothesis for aging

• What evidence supports this kind of hypothesis?

Correlation between biological age, cellular age and ‘appearance’?

Elissa Epel et al. 2004– telomere length of blood cells from mothers of healthy children and mothers caring for chronically ill children.

First: Chromosomes, Replication, Telomeres and Aging (vs Immortality)

• What is a chromosome?• Why copy chromosomes?• What happens when a cell doesn’t have

the correct number? (total number -- not talking about single mutations)

• Largest ‘pause’ in cell cycle-- G1/S transition. Hmm, why?

Process of copying DNA= DNA replication

CBI 5.4

Semi-conservative process requiring DNA helicase, primase, DNA polymerase, ligase, ssbinding proteins…..

Because both strands must be copied at same time-- ‘leading’ and ‘lagging’ strand.

So what about the ends?

• Telomeres: GGGTTA repeats:

uses in protection and attachment

• Why is their replication a problem?

• (How do gametes get around this?)

Hayflick meets End Replication Problem

Carol Greider and Calvin Harley: • Is this the ‘clock’? (early 1990s)

What is the consequence of high telomerase activity according to this

hypothesis?

Of having low telomerase activity?

• Greider and Haley: In adult humans only cells with high telomerase expression are germline cells and cancer cells—

Consistent?

• Looked at 1000 human primary cancers and saw 90% had increased telomerase activity

• BUT– HAVING high activity wasn’t enough to predict outcome

(acute myelocytic leukemia cases)

What if you could get rid of all telomerase

Predict the phenotype

Greider’s Telomerase free mice

• Chromosomes stick together or lost during division

• Mouse version of symptoms similar to Werner’s syndrome

• BUT– mice could still form tumors Getting rid of telomerase not enough to get rid of cancer.

Aging vs Immortality

If short telomeres lead to cell death do long telomeres lead to ‘immortal’ cell lines? What if you could turn telomerase back on? (Harley and Shay)

1998 Tom Brokaw announced

‘they have found a way to reverse the aging process’

(perhaps a bit overstated…..but)

• In Epel’s work– telomeres of ‘stress group’ 9-17 years shorter, appearance more aged than that of ‘less stress group’—

Consistent with hypothesis?What does this suggest about role

of environment?

What happens when you manipulate telomere length?

• Austriaco and Guarente paper

Big picture?

Why yeast?

What are they doing?