Genomes and Disease

www.womanstats.orgIndia: 933 girls/ 1000 boys Haryana: 834 girls/ 1000 boysChina: 837 girls / 1000 boys

Genomic data can be used for good or bad

Exclusion from insurance coverage for “pre-existing” genotypesGenetic discriminationEugenics

Genomes and Disease

What is a genetic “disease” as opposed to an acceptable trait?Is it a disease to be short statured? Below average intelligence?

Is it a disease to be gay?

Do we know enough about genomes and evolution to make germline changes?e.g. Certain alleles of hemoglobin cause Sickle Cell Anemia when homozygous, but protection from Malaria when heterozygous

How do we translate genome sequence into disease prediction?

Development and Disease: Disorders of Human Development

eyeless

Wild type

antennae wing

antennae leg

eyeless/Pax6 is necessary and sufficient for eye formation

Ectopic expression of eyeless/Pax6

Walter Gehring and colleagues

The eye specification regulatory network

Deep conservation of Pax 6 and eye development

Pax 6 is also required for eye specification in mouse

small eye phenotype is caused by being heterozygous for mutations in Pax 6

Homozygotes are lethal with no eyes

+/+

Pax 6 -/+

Pax 6 -/-

Expression of mouse Pax 6 makes eyes in Drosophila

Pax 6 mutants lead to congenital eye defects in humans

Pax6 +/- mutant leads to loss of iris (aniridia) along with other eye defects

Development and Disease: Disorders of Human Development

tinman (nkx2.5) mutants lack a heart

Mutations in Nkx2.5 cause congenital heart defectsPatients heterozygous for mutations exhibit a range of defects

A conserved heart specification network

National Vital Statistics Report May 2010 on data for 2007

Leading Causes of Death, United States 2007

Nkx2.5 is expressed in the adult mouse heart

The genes that control organ development can also control adult function and homeostasis

Nkx2.5 function is still required post-natally

PMID:18689573

CRE-ER to delete Nkx2.5 at birth

Heart contraction defects Reduced ion channel expression

Also showed direct Nkx2.5 regulation of ion channel genes50% mortality after 3 weeks

Tinman also regulates heart differentiation/function genes in Drosophila

dSUR is a component of an ATP-sensitive K+ channel that regulates heart physiology/stress response

dSUR is directly regulated by tinman and pannier (GATA)

Reductionof dSUR increases heart failure under stress

Disrupted lipid metabolism

aging

The Fly as a surprising model for adult heart physiology, disease and aging

ion channel disruption

National Vital Statistics Report May 2010 on data for 2007

Leading Causes of Death, United States 2007

What has/can Development teach us about Cancer?

-Cell-cell signaling-Cell fate specification and tumor cell origin-Differentiation/cell cycle arrest vs. dedifferentiation/proliferation-Growth control/tissue size restraint vs. independence-Apoptosis-Cell adhesion-Cell migration/metastasis-Vasculature development

Aging: The Inevitable? Disease

Walter Breuning, 114 years old (1896-2001)

Record: Jeanne Calment, 122 yrs, 164 days

The Oxygen Paradox: Oxygen is essential for aerobic respiration yet oxidative damage is toxic and a likely cause of senescence

Reactive oxygen species (ROS) cause:-Membrane fatty acid peroxidation-Protein modification/destruction-DNA damage

control

Protein oxidation

Lifespan

Extra SOD and catalase

The Oxygen Paradox: Oxygen is essential for aerobic respiration yet oxidative damage is toxic and a likely cause of senescence

Reactive oxygen species (ROS) cause:-Membrane fatty acid peroxidation-Protein modification/destruction-DNA damage

Metabolic Potential: There is an inherent limit to total amount of O2 consumed in a lifetime

-Decreased temperature extends lifespan in cold-blooded animals

-Flies that can’t fly live 2.5 times longer

-Inverse correlation b/w lifespan and reproduction

Caloric Restriction Increases Lifespan

Mice

Also true for Flies, Worms and Yeast!

During times of limited nutrients, it may be advantageious to switch metabolic resources from reproduction to somatic maintenance

BUT, Metabolic Potential Can’t be the Whole StoryCellular senescence is not inevitable: The Germline is immortal

Lifespans don’t always fit metabolic potential model: e.g. Mice live 2-3 yrs

Rats live 3 yrsSquirrels live 25 yrsBats live 30-50 yrs

e.g. Honey Bees-Queen and worker have same genotype-Worker lives few months-Queen lives up to 5 years-Queen eats copiously and constantly reproduces-It’s Good to be the Queen!

Can select for long-lived stocks in flies and lifespan mutants in different systems

Therefore, lifespan can be genetically programmed

Reproduction can be uncoupled from lifespan

daf-2age-1

2-3 fold increase in lifespan (=150-200 yrs old for human)

daf-16daf-18

Decrease lifespan

daf-2, clk-1 double mutant: 5-7 fold increase in lifespan= 500 years for human!!

Single Gene Mutations Can Dramatically Affect Lifespan

in C. elegans

daf = dauer formation defectiveDauer larvae: alternate developmental “stasis” stage

-increased stress tolerance-increased fat storage-decreased metabolism-decreased reproduction

Induced by starvation or other high-stress conditionsdauer phermone detected by sensory system

Mutants in Dauer Formation Also Show Effects on Lifespan

Link between stress resistance and longevityStress may also increase lifespan: Stress is good!

Some Lifespan Mutants are in the Insulin Signaling Pathway

37 in C. elegans

Signaling represses daf-

16

Nelson and Padgett, 2003

Activation normally decreases lifespan

Increased Lifespane.g. Superoxide dismutase

daf-16:GFP

chico

Insulin Receptor Pathway Regulates Lifespan in Flies and Mice

Nervous System Control Over Aging

wt mutanttransgene

All Cells All Neurons

Muscle Intestine

The Insulin Receptor Pathway is Required in the Nervous System

Note: other data indicates this pathway is also important in the worm intestine and fly fat body--both adipose tissues

BUT, the Nervous System Can Also Negatively Regulate Lifespan

Mutations affecting sensory neurons can increase lifespan

Smelling or tasting food may be as detrimental to lifespan as eating it!

L1 Adult

Z2, Z3 = germlineZ1, Z4 = somatic gonad

-Germline ablation increases lifespan-Blocking gametogenesis does not- Ablation of both germline and somatic gonad restores normal lifespan-Therefore, increase in lifespan is not directly due to reduced metabolic cost of not reproducing-Lifespan is regulated by SIGNALS from the germline through somatic gonad-Signal appears dependent on germline stem cells

Germline ablation causes daf-16 nuclear accumulation in adult intestine/adipose tissue

Animals with daf-16 expression only in intestine respond normally to germline ablation

Therefore, germline signal likely acts through daf-16 in intestine

C. Kenyon and colleagues

The Germline Signals to Activate Daf-16 in the Intestine

Reconciling (somewhat) metabolic and genetic models of agingThe same pathways that respond to metabolism can also be regulated genetically and subject to variation and evolution

AAsensing

Redoxsensing

Energysensing

Glucosesensing

Lifespan extension also decreases age-related diseases

-4-phenylbutyrate, histone deacetylase inhibitor(Sir2 is deacetylase, so unclear why inhibiting deacetylases would extend life)

-Treated flies have normal fecudity and movement-Treated flies are stress resistant (more healthy!)-Previously FDA approved for other uses