7. Gene Therapy Teacher

GENE THERAPY

Bagian Biokimia Fakultas Kedokteran Universitas Hasanuddin Makassar

Dr. Marhaen Hardjo, M.Biomed, PhD

DNA sequence

↓

mRNA sequence

↓

Polypeptide

Gene mutations which affect only one gene

Transcription

Translation

© 2010 Paul Billiet ODWS

http://www.saburchill.com/IBbiology/bio_hp.html

DNA (antisense strand)

mRNA

Polypeptide

Normal gene

GGTCTCCTCACGCCA

↓

CCAGAGGAGUGCGGU

Codons

↓

Pro-Glu-Glu-Cys-Gly

Amino acids

The antisense strand is the DNA strand which acts as the template for mRNA transcription



Mutations: Substitutions

Substitution mutation

GGTCACCTCACGCCA

↓

CCAGUGGAGUGCGGU

↓

Pro-Arg-Glu-Cys-Gly

Substitutions will only affect a single codonTheir effects may not be serious unless they affect an amino acid that is essential for the structure and function of the finished protein molecule (e.g. sickle cell anaemia)

Normal gene

GGTCTCCTCACGCCA

↓

CCAGAGGAGUGCGGU

Codons

↓

Pro-Glu-Glu-Cys-Gly

Amino acids



The genetic code is degenerate

A mutation to have no effect on the phenotype

Changes in the third base of a codon often have no effect.



No change

Normal gene

GGTCTCCTCACGCCA

↓

CCAGAGGAGUGCGGU

Codons

↓

Pro-Glu-Glu-Cys-Gly

Amino acids


GGTCTTCTCACGCCA

↓

CCAGAAGAGUGCGGU

↓

Pro-Glu-Glu-Cys-Gly



Disaster

Normal gene

GGTCTCCTCACGCCA

↓

CCAGAGGAGUGCGGU

Codons

↓

Pro-Glu-Glu-Cys-Gly

Amino acids


GGTCTCCTCACTCCA

↓

CCAGAAGAGUGAGGU

↓

Pro-Glu-Glu-STOP



Mutations: Inversion

Normal gene

GGTCTCCTCACGCCA

↓

CCAGAGGAGUGCGGU

Codons

↓

Pro-Glu-Glu-Cys-Gly

Amino acids

Inversion mutation

GGTCCTCTCACGCCA

↓

CCAGGAGAGUGCGGU

↓

Pro-Gly-Glu-Cys-Gly

Inversion mutations, also, only affect a small part of the gene



Mutations: Additions

Normal gene

GGTCTCCTCACGCCA

↓

CCAGAGGAGUGCGGU

Codons

↓

Pro-Glu-Glu-Cys-Gly

Amino acids

Addition mutation

GGTGCTCCTCACGCCA

↓

CCACGAGGAGUGCGGU

↓

Pro-Arg-Gly-Val-Arg

A frame shift mutation



Mutations: Deletions

Normal gene

GGTCTCCTCACGCCA

↓

CCAGAGGAGUGCGGU

Codons

↓

Pro-Glu-Glu-Cys-Gly

Amino acids

Deletion mutation

GGTC/CCTCACGCCA

↓

CCAGGGAGUGCGGU

↓

Pro-Gly-Ser-Ala-Val

A frame shift mutation



Mutations of haemoglobin

• Haemoglobin is a tetramer = 2 and 2 -chains• The genes for these polypeptides are found on

different chromosomes• The -chain gene is found on chromosome 11• The -chain gene is found on chromosome 16• The nucleotide sequences have been worked

out• Several inherited diseases occur on the -chain,

which contains 146 amino acids.



haemoglobin sense strand cDNA sequence

• cDNA (complementary DNA) is obtained by back-transcribing the mRNA used to translate the polypeptide

• So cDNA has no introns

• This is done using reverse transcriptase enzyme.



ATG GTG CAT CTG ACT CCT GAG GAG AAG TCT GCC GTT ACT GCC CTG TGG GGC AAG GTG AAC GTG GAT GAA GTT GGT GGT GAG GCC CTG GGC AGG CTG CTG GTG GTC TAC CCT TGG ACC CAG AGG TTC TTT GAG TCC TTT GGG GAT CTG TCC ACT CCT GAT GCT GTT ATG GGC AAC CCT AAG GTG AAG GCT CAT GGC AAG AAA GTG CTC GGT GCC TTT AGT GAT GGC CTG GCT CAC CTG GAC AAC CTC AAG GGC ACC TTT GCC ACA CTG AGT GAG CTG CAC TGT GAC AAG CTG CAC GTG GAT CCT GAG AAC TTC AGG CTC CTG GGC AAC GTG CTG GTC TGT GTG CTG GCC CAT CAC TTT GGC AAA GAA TTC ACC CCA CCA GTG CAG GCT GCC TAT CAG AAA GTG GTG GCT GGT GTG GCT AAT GCC CTG GCC CAC AAG TAT CAC TAA

Methionine initiator

Nonsense terminator© 2010 Paul Billiet ODWS


Mutation Codon Change to DNA sense strand

Change in Amino Acid

S (sickle cell anaemia)

6 GAG to GTG Glu to Val

C (cooley’s syndrome)

6 GAG to AAG Glu to Lys

GSan Jose 7 GAG to GGG Glu to Gly

E 26 GAG to AAG Glu to Lys

MSaskatoon 63 CAT to TAT His to Tyr

MMilwauki 67 GTG to GAG Val to Glu

OArabia 121 GAA to GTA Glu to Val


Sickle Cell Anaemia

Blood smear (normal)Image Credit: http://lifesci.rutgers.edu/~babiarz/

Sickle cell anemiaImage Credit: http://explore.ecb.org/

Diseases for applying gene therapy

Disease Defect Target cell

Severe combined Bone marrow cells or

immunodeficiency T-lymphocytes

Hemophilia Liver, muscle

Cystic fibrosis Lung Cells

Cancer Many cell types

Neurological diseases Parkinson’s/ Alzheimers Nerve Cells

Infectious diseases AIDS, hepatitis B White Blood Cells

Gene therapy could be very different for different diseases

• Gene transplantation (to patient with gene deletion)

• Gene correction (To revert specific mutation in the gene of interest)

• Gene augmentation (to enhance expression of gene of interest)

Gene therapy

In vivo Ex vivo

in vivo and ex vivo schemes

http://laxmi.nuc.ucla.edu:8237/M288/SChow_4_10/sld005.htm

IN VIVO

EX VIVO

1. The genetic material is transferred directly into the body of the patient

2. More or less random process; small ability to control; less manipulations

3. Only available option for tissues that can not be grown in vitro;

or if grown cells can not be transferred back

In vivo gene therapy

1. The genetic material is first transferred into the cells grown in vitro

2. Controlled process; Genetically altered cells are selected and

expanded; more manipulations

3. Cells are then returned back to the patient

Ex vivo gene therapy

Injections of naked DNA

Current attempts with naked DNA vaccination in infectious diseases

HIV HepatitisInfluenza

Tuberculosis,

Lyme disease

Malaria

Ballistic DNA Injection (gene guns)

Invented for DNA transfer to plant cells

Fully applicable to eukaryotic cells

plasmid DNA shown here

LiposomesNext level idea – why naked DNA?

Lets’ wrap it in something safe to increase transfection rate

Therapeutic drugs

Lipids – are an obvious idea !

DNA delivery of genes by liposomes

Cheaper than viruses

No immune response

Especially good for in-lung delivery (cystic fibrosis)

100-1000 times more plasmid DNA needed for the same transfer efficiency as for viral vector

Cystic fibrosismost common lethal genetic disorder in Caucasian populations (1 in 2000 live births.) . Among African and Asian is really rare

a defect in the CFTR gene

Lungs create thick mucus secretion(prone to infections,

constant cough, leading cause of death)

Lungs in cystic fibrosisNormal lung CF lungs

dilated crypts filled with mucus and bacteria.

Normal alveolar appearance

CF lungs filled with mucus lung did not collapse when it was removed postmortem

Cystic fibrosis lungs are prone to infections

The battle between WBC’s and bacteria leads ultimately to lung fibrosis and damage

"Hyperinflammation" and WBC’s unable to eradicate bugs, instead damage lung tissue.

Mucus protects bugs

MOST COMMON VIRAL VECTORS

Retroviruses

Herpes simplex viruses

can create double-stranded DNA copies of their RNA genomes. Can integrate into genome. HIV for example

dsDNA viruses that infect a neurons. Cold sores virus

Retroviral vectors are able to infect dividing cells only

Good for cancer gene therapy

So, retroviruses are most often used vectors for common disease gene therapy

In dividing cells nuclear membranes are broken down, so viral genome can enter and integrate into the chromosome

Real treatments performed with retroviral system

Severe Combined Immunodoficiency (SCID)Mutation on Chromosome 20 is often to blame

What is Severe Combined Immunodoficiency (SCID)?

> 8 new ear infections per year

> 2 serious sinus infections per year

> 2 month on antibiotics with little effect

> 2 pneumonias per year

-- failure to gain weight and grow

-- recurrent deep skin and organ abscesses

SCID treatments

Life in germ-free envinronment

Bone-marrow transplantations

Enzyme replacement therapy VERY expensive; not a cure; temporary effect

GENE THERAPY

7. Gene Therapy Teacher

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