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| Undergraduate Research Abstract |
Chien-Jou Chen One of the DNA MMR(mismatch repair) genes which have an impact on the frequency of DNA mutations and thus mitotic recombination in cells is Mlh1.(1) Mlh1 is part of a group of genes called the MMR(DNA mismatch repair) genes, these genes locate and repair mutations throughout the genome. MLH1a functions in three complexes; Mlh1-Pms2(MutL), Mlh1-Pms1(MutLb) and Mlh1-Mlh3(mutLg). The MutLa complex carries out the primary function of all the MutL complexes within mitotic cells.(1) MutS complexes recognize insertion and deletion loops(mutations in bases) within the genome and recruits MutLa complex to initiate repair events which fix the base mutations.(1) It has been found that Mlh1 has been associated with HNPCC(hereditary nonpolyposis colorectal cancer) which is almost 5% of all colon cancer cases in the United states.(1) HNPCC patients start with heterozygous MMR genes one of which is Mlh1. In HNPCC tumors when the wild-type Mlh1 allele is lost due to LOH by either mitotic recombination or functionality, tumors become genetically unstable and thus more and more genomic mutations are acquired.(1) In addition, It has also been shown that Microsatellite instability in a large number of HNPCC patients is caused by LOH mutations in MLH1.(1) (Microsatellite instability is the insertion or deletion of base pairs in mononucleotide to base pair repeats). The experiment that I have been working on is analyzing the instability of a microsatellite of 24 Adenine repeats in mice at locus U12235 which do not have tumors and have not been treated with radiation with genotypes Mlh1+/+, +/-, and -/-. The purpose of this experiment is to statistically show how each different Mlh1 genotype efficiently fixes Microsatellite base mutations within the genome. This study tests whether Mlh1 is haploid sufficient by comparing the three different genotypes. This experiment will hopefully help point future studies in the right direction in figuring out as to why Microsatellite instability due to deficient Mlh1 leads to HNPCC tumorigenesis and not other cancers. The tail cells of mice were used in this experiment. The samples were diluted so that one microliter of solution contained one genome. Each genome is amplified hoping to only have 1 copy of the U12235 locus is amplified. Then the PCR products are analyzed to find the mutations in the microsatellite of mononucleotide adenine repeats. Thus far our data has shown that mice with genotype Mlh1+/+ hashave the lowest amount of microsatellite instability, while Mlh1 -/- has the highestt rate of microsatellite instability while and Mlh1 heterozygous has a rate between the two.
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last updated Aug 24, 2005 |
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