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Molekulare Diagnostik
1Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
PCR(polymerase chain reaction)
Definition:Ist ein in vitro Verfahren zur selektiven Anreicherung von Nukleinsäure-Bereichen definierter Länge und definierter Sequenz aus einem Gemisch von Nukleinsäure-Molekülen
Molekulare Diagnostik
2Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
PCR-History• Erfunden 1983 von Dr. Kary Mullis• Er erhielt 10 Jahre später den Nobelpreis für
Chemie• Seit 1992 tausende Zitate in Publikationen • PCR hat extrem viele Anwendungsgebiete
(Vaterschaftstest, Gerichtsmedizin, Krankheitsnachweise, Sequenzierung…..)
Molekulare Diagnostik
3Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Prinzip PCR• Welche Nukleinsäuresequenz soll
amplifiziert werden?• Welche DNA wird als Vorlage-Template
verwendet (Genomische, cDNA…)
• Primer setzen und suchen (Kriterien)• Temperaturprogramm wählen• DNA aus PCR Gemisch isolieren• Weiterverwendung der isolierten DNA
Molekulare Diagnostik
4Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Primer setzen und suchen
• Primer im Randbereich der zu amplifizierenden Sequenz setzen (5´- 3´Amplifikation)
• Komplementär zu je einem Strang• Parameter:
– Primerlänge– Ampliconlänge– Schmelztemperatur (Verhältnis G:C zu A:T beachten!!)– 3‘ clamp– Primerdimere vermeiden
Molekulare Diagnostik
5Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
PCR-Gemisch
• Template DNA (100 ng cDNA, 500 ng genomische DNA)
• Primer (10 µmolar)• DNA-Polymerase Taq (Bakt Thermus aquaticus)• dNTPs (Nukleosidtriphosphate)• PCR-Puffer• dd H2O• Optionale Zusätze: MgCl2, DMSO
Molekulare Diagnostik
6Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Temperatur- und Zeitprogramm• Denaturieren zum Einzelstrang (94°C, 30 sec)• Anhybridisieren der Primer (Annealing, 30 sec)
kommt auf die Schmelztemperatur der Primer an:je höher die Temperatur umso spezifischer das PCR-Produkt
• Amplifizieren mittels DNA-Polymersase (72°C, 2-4 min)kommt auf Größe des Produkts an!!mittels hitzestabiler Taq-Polymerase(proof reading oder nicht?)
Molekulare Diagnostik
7Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Molekulare Diagnostik
8Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Kontrolle und Isolierung der DNA aus PCR Gemisch
• Gelelektrophorese:– Wie groß ist das erwartete PCR-Produkt?– Welches Agarosegel verwendet man (meist 0,7-2%)?– Ist nur ein Produkt sichtbar oder mehrere?
bei vielen Banden unspezifische PCR– Ausschneiden der spezifischen DNA-Bande aus dem
Gel– Isolieren der DNA aus dem Gelstückchen (Kit)– Sequenzierung
Molekulare Diagnostik
9Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Laufrichtung DNA auf Agarosegel
Molekulare Diagnostik
10Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Agarosegel zur Auftrennung des PCR-Gemisches
Molekulare Diagnostik
11Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Agarosegel zur Auftrennung des PCR-Gemisches
Molekulare Diagnostik
12Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Einsatzmöglichkeiten der PCR• Amplifikation von DNA Bereichen• cDNA-Klonierung und cDNA-Genbanken• Herstellung von cDNA-chips • DNA-Foot- & Fingerprinting• DNA und RNA (cDNA)-Sequenzierung• Isolierung, Markierung und Mutagenisierung von DNA-
Fragmenten• Diagnostik:
– Gen-Diagnostik (genetische Erkrankungen)– Krebsdiagnostik: genomische Translokationen– Diagnostik infektiöser Krankheiten
Molekulare Diagnostik
13Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
REAL TIME PCR(= quantitative PCR (qPCR))
• Real time PCR systems• Fluorescence chemistry• Analysis
Molekulare Diagnostik
14Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Real-time PCR for gene expression analysis
2a. excitation filters
2b. emission filters
1. halogen tungsten lamp
4. sample plate
3. intensifier
5. CCD chip
Allows real time monitoring of PCR amplification products by use of fluorescenceFirst step: Reverse transcription of RNA into complementary DNA (cDNA)Mainly semi-quantitative measurement (qPCR)Highly sensitiveUsed in research lab and clinical diagnostic labs
Real time-PCR systems
Molekulare Diagnostik
15Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Real time-PCR systems
Molekulare Diagnostik
16Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Real time-PCR systems
Molekulare Diagnostik
17Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Real time-PCR systems
Molekulare Diagnostik
18Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Real time-PCR systems
Molekulare Diagnostik
19Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Importance of primers in PCR
• specific• high efficiency• no primer-dimers• Ideally should not give a DNA signal
– cross exon/exon boundary
EXON 1 EXON 2INTRON 2 DNA
EXON 1 EXON 2 RNA
Real time-PCR chemistries
Molekulare Diagnostik
20Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Fluorescence chemistry for real-time PCRSybrGreen intercalating dye:TaqManTM probe uses FRET
(Flueorescent resonance energy transfer):
Real time-PCR chemistries
Molekulare Diagnostik
21Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
TaqManBiomaterials
21Institute for Genomics and Bioinformatics, TU Graz / Austria Dr. Andreas Prokesch
Real time-PCR chemistries
Molekulare Diagnostik
22Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Real time-PCR chemistries
Molekulare Diagnostik
23Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Real time-PCR chemistries
Molekulare Diagnostik
24Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Real time-PCR chemistries
Molekulare Diagnostik
25Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Fluorescence resonance energy transfer
Real time-PCR chemistries
Molekulare Diagnostik
26Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Real time-PCR chemistries
Molekulare Diagnostik
27Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Real time-PCR chemistries
Molekulare Diagnostik
28Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Real time-PCR chemistries
Passive dye
TaqMan reporter
TaqMan reporter
TaqMan quencher
Molekulare Diagnostik
29Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Real time-PCR chemistries
Molekulare Diagnostik
30Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Real time-PCR chemistries
Molekulare Diagnostik
31Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Real time-PCR chemistries
Molekulare Diagnostik
32Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Real time-PCR analysis
Molekulare Diagnostik
33Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
0
200000000
400000000
600000000
800000000
1000000000
1200000000
1400000000
1600000000
0 5 10 15 20 25 30 35
PCR CYCLE NUMBERA
MO
UN
T O
F D
NA
110
1001000
10000100000
100000010000000
1000000001000000000
10000000000
0 5 10 15 20 25 30 35
PCR CYCLE NUMBER
AM
OU
NT
OF
DN
A
CYCLE NUMBER AMOUNT OF DNA0 11 22 43 84 165 326 647 1288 2569 512
10 1,02411 2,04812 4,09613 8,19214 16,38415 32,76816 65,53617 131,07218 262,14419 524,28820 1,048,57621 2,097,15222 4,194,30423 8,388,60824 16,777,21625 33,554,43226 67,108,86427 134,217,72828 268,435,45629 536,870,91230 1,073,741,82431 1,400,000,00032 1,500,000,00033 1,550,000,00034 1,580,000,000
Plotting PCR in real-time
Real time-PCR analysis
Molekulare Diagnostik
34Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
34
Reference genes
• same copy number in all cells• expressed in all cells• medium copy number advantageous
– correction more accurate• reasonably large intron• no pseudogene• no alternate splicing in region you want
to PCR
Molekulare Diagnostik
35Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Importance of controls
• negative control (no DNA)– checks reagents for contamination
• no reverse transcriptase control– detects if signal from contaminating DNA
• positive control– checks that reagents and primers work– especially importance if trying to show
absence of expression of a gene
Molekulare Diagnostik
36Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Amplification curve to determine realtive expression values
Output: relative fold-change(for semiquantitative qPCR)
Real time-PCR analysis
Molekulare Diagnostik
37Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Melting curve as quality control for SybrGreen assays
Real time-PCR analysis
Molekulare Diagnostik
38Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Diagnostic use of real-time PCR
• Quantitatively measurment of Human Immunodeficiency Virus (HIV)• Detection of Thalassemia, hemophilia, sickle cell anemia & favism by
real time PCR• Cystic fibrosis• Phenyl ketonuria• Use in forensic medicine• Noninvasive Prenatal Diagnosis by Analysis of Fetal DNA in Maternal
Plasma• Detection and Quantitation of Circulating Plasmodium falciparum DNA• Effect of antimicrobial peptides on host cells• …
Molekulare Diagnostik
39Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Pros and cons of real-time PCR
• Pros– Simple– Low cost– Good sensitivity– High dynamic range
• Cons– Big reaction volumina– Dependence on reference genes– Limited specificity (especially with
SybrGreen)– No absolute quantification!!!
Limited use for detection of allelic imbalances, Limited use for detection of allelic imbalances, exact copy number variations and rare mutationsexact copy number variations and rare mutations
Molekulare Diagnostik
40Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Digital PCR
Emulsion Array Chip
Molekulare Diagnostik
41Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Digital PCR - Principle
•Sample partitioning via limited dilution•Detection via fluorescent probes•Read out: positive or negative reaction (0 or 1)•Absolute quantification by counting of positive reactions
Molekulare Diagnostik
42Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Emulsion-based system(QX100 Droplet Digital PCR, Biorad)
http://www.youtube.com/watch?v=Qwma-1Ek-Y4
Molekulare Diagnostik
43Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
http://www.youtube.com/watch?v=1ltLsAosmY0
Array-based system(OpenArray Digital PCR, Life Technologies)
Molekulare Diagnostik
44Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
Array-based Capillary System(Biomark DigitalArray, Fluidigm)
http://vimeo.com/14655746
Molekulare Diagnostik
45Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
dPCR facilitates detection and dPCR facilitates detection and quantification of...quantification of...
•• Rare mutationsRare mutations•• Copy number variationsCopy number variations•• Karyotypic events (cytogenetics)Karyotypic events (cytogenetics)•• LowLow--level pathogenslevel pathogens•• Gene expression in single cellsGene expression in single cells•• Clonal amplification of nucleic acidsClonal amplification of nucleic acids
Molekulare Diagnostik
46Institute for Genomics and Bioinformatics, TU Graz / Austria Dr.Andreas Prokesch
The PCR songhttp://www.youtube.com/watch?v=_zxr-52KwKo&feature=related