L5 - tumour suppressor genes Flashcards
What happens when you fuse cancer and non-cancer cells and introduce these cells into nude mice?
The cells form heterokaryons. If cancer was a dominant gene there would be tumour formation but there is not.
What is retinoblastoma?
A cancer of the retina. Can be sporadic (unilateral) or familial (bilateral)
Do people with Rb have a high chance of developing another cancer?
Yes, 1:3
How do we find TS genes?
RLFP and now SNPs
How has Rb contributed to our understanding of TS genes?
2-hit hypothesis
- If unilateral (sporadic) the genome must undergo 2 separate mutations to lose both alleles therefore the pattern of appearance of patients with unilateral Rb is curved
- If bilateral (inherited) the genome is already missing one wt allele and therefore only needs 1 hit. The curve is then linear
Need 2 hits of the genome to cause a tumour, if the first hit is inherited, only 1 needs to occur therefore patients who inherit the first hit are more likely to have bilateral Rb as they only need one more hit
How is the frequency of the loss of the second wt allele explained?
Homologus recombination (crossing over) and epigenetic silencing are much more common than mutations that inactivate the protein product
How can LOH be identified?
Cytogenetics - look at banding pattern
Zymography - use marker that is found in the suspected part of the chromosome that is lost e.g. D esterase is found near Rb locus. Can measure levels of D esterase. In heterozygous Rb patients there is a loss of 1 band (normal people have 2 bands)
How do RFLPs work?
Use restriction enzymes to fragment a chr into known sizes. Run the fragments on a gel and probe with known seq/pattern. If there is a difference in the fragment sizes/number of fragments when compared to a wt gel then we know that there has been a loss of a part of the chromosome. We can now use SNPs to do this.
