title: Mature microsatellites: mechanisms underlying dinucleotide microsatellite mutational biases in human cells.
abstract: Dinucleotide microsatellites are dynamic DNA sequences that affect genome stability. Here, we focused on mature microsatellites, defined as pure repeats of lengths above the threshold and unlikely to mutate below it in a single mutational event. We investigated the prevalence and mutational behavior of these sequences by using human genome sequence data, human cells in culture, and purified DNA polymerases. Mature dinucleotides (≥10 units) are present within exonic sequences of >350 genes, resulting in vulnerability to cellular genetic integrity. Mature dinucleotide mutagenesis was examined experimentally using ex vivo and in vitro approaches. We observe an expansion bias for dinucleotide microsatellites up to 20 units in length in somatic human cells, in agreement with previous computational analyses of germ-line biases. Using purified DNA polymerases and human cell lines deficient for mismatch repair (MMR), we show that the expansion bias is caused by functional MMR and is not due to DNA polymerase error biases. Specifically, we observe that the MutSα and MutLα complexes protect against expansion mutations. Our data support a model wherein different MMR complexes shift the balance of mutations toward deletion or expansion. Finally, we show that replication fork progression is stalled within long dinucleotides, suggesting that mutational mechanisms within long repeats may be distinct from shorter lengths, depending on the biochemistry of fork resolution. Our work combines computational and experimental approaches to explain the complex mutational behavior of dinucleotide microsatellites in humans.
authors: Intercollege Graduate Program in Genetics, Huck Institutes of Life Sciences, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
authors: Beverly A
authors: BA
authors: Baptiste
authors: Guruprasad
authors: G
authors: Ananda
authors: Noelle
authors: N
authors: Strubczewski
authors: Andrew
authors: A
authors: Lutzkanin
authors: Su Jen
authors: SJ
authors: Khoo
authors: Abhinaya
authors: A
authors: Srikanth
authors: Nari
authors: N
authors: Kim
authors: Kateryna D
authors: KD
authors: Makova
authors: Maria M
authors: MM
authors: Krasilnikova
authors: Kristin A
authors: KA
authors: Eckert
mesh_terms: D001483:Base Sequence; D002461:Cell Line, Transformed; D053843:DNA Mismatch Repair / Q000235:genetics*; D004252:DNA Mutational Analysis / Q000379:methods*; D019951:DNA Polymerase beta / Q000235:genetics / Q000378:metabolism; D045643:DNA Repair Enzymes / Q000235:genetics / Q000378:metabolism; D004261:DNA Replication; D005822:Genetic Vectors; D015894:Genome, Human; D042822:Genomic Instability; D045325:HCT116 Cells; D006801:Humans; D018895:Microsatellite Repeats; D000070956:MutL Proteins; D016296:Mutagenesis; D059645:Mutation Rate; D018741:Replication Origin
chemical_list: C500929:MutLalpha protein, human; D019951:DNA Polymerase beta; D000070956:MutL Proteins; D045643:DNA Repair Enzymes
keywords: microsatellite instability; mismatch repair; short tandem repeats; strand slippage