The role of Drosophila mismatch repair in suppressing recombination between diverged sequences.

Anthony T Do,Jeannine R Larocque

doi:10.1038/srep17601

Anthony T Do, Jeannine R Larocque

Open Access

https://doi.org/10.1038/srep17601

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Abstract

DNA double-strand breaks (DSBs) must be accurately repaired to maintain genomic integrity. DSBs can be repaired by homologous recombination (HR), which uses an identical sequence as a template to restore the genetic information lost at the break. Suppression of recombination between diverged sequences is essential to the repair of DSBs without aberrant and potentially mutagenic recombination between non-identical sequences, such as Alu repeats in the human genome. The mismatch repair (MMR) machinery has been found to suppress recombination between diverged sequences in murine cells. To test if this phenomenon is conserved in whole organisms, two DSB repair systems were utilized in Drosophila melanogaster. The DR-white and DR-white.mu assays provide a method of measuring DSB repair outcomes between identical and diverged sequences respectively. msh6–/– flies, deficient in MMR, were not capable of suppressing recombination between sequences with 1.4% divergence, and the average gene conversion tract length did not differ between msh6–/+ and msh6–/–flies. These findings suggest that MMR has an early role in suppressing recombination between diverged sequences that is conserved in Drosophila.

Highlights

homologous recombination (HR) using an identical sequence is highly regulated, as recombination between diverged, or non-identical, sequences is suppressed in many organisms including yeast[6], mammals[7,8], and Drosophila[9]
Suppression of recombination between diverged sequences is due in part to the function of the mismatch repair (MMR) machinery[6,8,12,13], which recognize mismatches formed in heteroduplex DNA where one strand is from the donor sequence used as a template for repair and the other from the sequence containing the double-strand break (DSB)
Findings from previous studies suggest that the role of MMR proteins in suppressing recombination between diverged sequences is conserved across yeast[6,13], E. coli[12], and murine cells[8]

Summary

Introduction

HR using an identical sequence is highly regulated, as recombination between diverged, or non-identical, sequences is suppressed in many organisms including yeast[6], mammals[7,8], and Drosophila[9]. In the absence of MMR, no downstream proteins are recruited to abort recombination, despite any divergence in sequence[13,19]. It is unknown if the role of MMR in suppressing recombination between diverged sequences is conserved in multicellular systems. Futhermore, gene conversion tract (GCT) lengths between msh6–/– and msh6–/+ flies were found to be similar These findings suggest that MMR suppresses recombination between diverged sequences in Drosophila and the similar GCT lengths suggest that MMR components act on the repair intermediate prior to repair synthesis

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