Screening for Complex Phenotypes

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1 Screening for Complex Phenotypes Michael Hemann

2 Screening for cancer phenotypes in mice

3 How do we typically model cancer in mice? Tumor Suppressor KO Oncogene transgenesis

4 Problems with conventional mouse models Limited to one/few cancer gene alteration(s) per mouse Mouse breeding is slow Alterations are present throughout development All cells have the cancer lesion Screening is not feasible

5 Can forward genetics screens be performed in mice?? Genetic screens

6 Using mobile genetic elements to introduce cancer-causing changes into somatic tissues Retroviruses Transposons

7 What are retroviruses? RNA viruses RNA Reverse Transcription RNA DNA Integration

8 Examples of retroviruses HIV HTLV-3 (Human T cell Leukemia Virus) M-MuLV (Moloney Murine Leukemia Virus)

9 Viruses can cause cancer Did you know that there's a common virus that can cause cancer?

10 DNA viruses Promote cancer through expression of virally encoded proteins E6 p53 HPV E7 Rb

11 Retroviruses Promote cancer by altering the expression of host genes Enhancer - Promotor capsid RT envelope Enhancer - Promotor 5 LTR M-MuLV 3 LTR Viral Integration c-myc Genomic DNA up to 270kb

12 Gene therapy and insertional mutagenesis γc cytokine receptor deficiency Gag April, 2000 γc cytokine receptor M-MuLV 5 LTR Ψ+ M-MuLV 3 LTR Retroviruses induced T cell leukemias October, 2003

13 Objective: Use retroviral insertional mutagenesis to identify oncogenes M-MuLV IP injections

14 Experimental approach Infect newborn mice Wait for tumor development Harvest tumors Use a PCR strategy to clone insertion sites Identify proximal cancer gene(s)

15 Identifying Common Insertion Sites (CIS) CIS - an insertion site in multiple, independent tumors Normal Cells Blue = M-MuLV Red = Lentivirus Cancer Cells Red and Green = CISs 50 CISs

16 Questions How are insertion sites identified? How many insertions are present in each tumor? Why do they start with Pim-1/Pim-2 KO mice? What kinds of genes are identified using this approach?

17 Transposons Sequences of DNA that can move around to different positions within the genome of a single cell Class 1 - Retrotransposons LTR LINEs SINEs 45% of the human genome Class 2 - DNA transposons

18 Transposons are insertional mutagens Class 1 - Retrotransposons Factor VIII gene LINE insertions resulting in haemophilia

19 Transposons are insertional mutagens Class 1 - DNA transposons P elements in fruit flies Ac/D in corn

20 DNA transposons in higher eukaryotes Inv. Rep./Dir. Rep. Tc1/mariner DNA transposon transposase Inv. Rep./Dir. Rep. * * * * * * * * * * * * * Not active due to accumulated mutations Sleeping Beauty

Fish, and Its Transposition in Human Cells.

21 Waking sleeping beauty Salmon Tc1 transposon Molecular Reconstruction of Sleeping Beauty, a Tc1-like Transposon from Fish, and Its Transposition in Human Cells. Cell, Volume 91, Issue 4, Pages Z. Ivics, P. Hackett, R. Plasterk, Z. Izsvák

22 When sleeping beauty wakes up Cut and paste transposition Sleeping beauty Genomic DNA AT Integration (using transposase) Excision (using transposase) Insertion site scarring

23 Objective: Use transposon insertional mutagenesis to identify oncogenes and tumor suppressor genes Sleeping beauty Cancer gene

24 Sleeping Beauty in mice Splitting up the transposon T2/Onc2 Modified transposon w/o transposase X RosaSB Rosa26 transposase Tg/+;SB/+ Cancer phenotypes?

25 Modified transposon No transposase SA pa MSCV 5 LTR SD SA pa Splice acceptor/ poly A signal MSCV LTR promotor and splice donor Inverted splice acceptor/poly A signal

26 Experimental approach Cross transposon and transposase mice Wait for tumor development Harvest tumors Use a PCR strategy to clone insertion sites Identify proximal cancer gene(s)

27 Questions How are insertion sites identified? How many insertions are present in each tumor? How does insertion site scarring impact these experiments? What kinds of genes are identified using this approach? Why is there embryonic lethality? How can this be avoided?

28 More questions What are the strengths and weaknesses of each approach? How could these systems be adapted to uncover broader classes of cancer genes?

Breeding scheme, transgenes, histological analysis and site distribution of SB-mutagenized osteosarcoma.

Supplementary Figure 1 Breeding scheme, transgenes, histological analysis and site distribution of SB-mutagenized osteosarcoma. (a) Breeding scheme. R26-LSL-SB11 homozygous mice were bred to Trp53 LSL-R270H/+