Microsatellite Instability: From Molecular Mechanisms to Repeat Expansion Diseases

Dear Colleagues,

Microsatellites are simple repetitive DNA sequences present in prokaryotic and eukaryotic genomes. Due to their high instability, consisting of the addition or deletion of repeated units, they have been referred to as dynamic mutations.

Although they have been classically used as molecular markers, microsatellite instability is assumed to play a relevant role in the evolution of genomes. Moreover, the instability of repeated sequences can be a source of phenotypic variation in bacterial pathogens, be linked to neurodegenerative diseases in humans, or be a major feature in certain types of cancer. Numerous genetic assays and biochemical analyses indicate a relevant role of DNA replication, DNA repair and transcription machineries in generating instability of microsatellite repeats. Small-scale instability is supposed to occur by the local misalignment of DNA as a consequence of the blockage of DNA replication within a repeated region that is promoted by a defective replication machinery or the formation of Non-B DNA structures at the repeat. Large expansions of trinucleotide repeats, as observed in more than 50 repeat expansion diseases including Huntington's disease, multiple spinocerebellar ataxias or fragile X syndrome, and are not uniquely explained by the DNA slippage model but more complex mechanisms including the formation of R-loops.

This Special issue welcomes manuscripts including the molecular mechanistic details of DNA microsatellite instability from in vitro model systems to Bacteria and Eukaryotes, their role as biomarkers and their relationship to Repeat Expansion Diseases.

Prof. Dr. Enrique Viguera
Guest Editor

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• microsatellite
• DNA instability
• DNA replication
• DNA repair
• DNA Recombination
• replication slippage
• misalignment
• repeat expansion
• trinucleotide repeats
• genetic anticipation
• dynamic mutations
• fragile X syndrome
• Huntington's disease
• Friedreich’s ataxia

Title: Effect of SSB binding modes on the slippage error produced by T7 DNA polymerase during replication of DNA repeated sequences

Abstract: DNA replication is a highly intricate process crucial for the faithful transmission of genetic information. Despite the remarkable fidelity of DNA polymerases, errors can occur, and replication slippage represents a notable source of genetic instability. This phenomenon involves the transient dissociation and subsequent reannealing of DNA strands during replication, leading to the insertion or deletion of repetitive sequences.
Single-stranded DNA binding proteins (SSBs) play a pivotal role in DNA replication by stabilizing single-stranded regions, preventing secondary structure formation, and facilitating the interaction of various replication proteins with the template. Recent studies have shed light on the intricate interplay between SSB proteins and replication slippage errors.
We show in this work that SSB affects fidelity of replication of T7 DNA polymerase by stimulating its SDA, when SSB is in (SSB)56 binding mode; we also show that this stimulation is specific for T7 DNA polymerase, since SSB in neither (SSB)56 nor (SSB)65, does not affect slippage efficiency of T4 DNA polymerase. Furthermore this effect is specific of E. coli SSB, in which binding modes have been described (8-12), since SSB from T4, T7 and from Bacillus subtilis do not stimulate SDA of T7 DNA polymerase. This could indicate the existence of interactions between SSB, in either of its binding modes, and T7 DNA polymerase.