Current Biology
Volume 27, Issue 1, 9 January 2017, Pages 96-102
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Bloom Syndrome Helicase Promotes Meiotic Crossover Patterning and Homolog Disjunction

https://doi.org/10.1016/j.cub.2016.10.055Get rights and content
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Highlights

  • Blm is essential for the primary meiotic recombination pathway in Drosophila

  • In Blm mutants, interference and other types of crossover patterning are lost

  • In Blm mutants, meiotic crossovers are made on chromosome 4

  • Loss of regulated crossover designation leads to elevated nondisjunction

Summary

In most sexually reproducing organisms, crossover formation between homologous chromosomes is necessary for proper chromosome disjunction during meiosis I. During meiotic recombination, a subset of programmed DNA double-strand breaks (DSBs) are repaired as crossovers, with the remainder becoming noncrossovers [1]. Whether a repair intermediate is designated to become a crossover is a highly regulated decision that integrates several crossover patterning processes, both along chromosome arms (interference and the centromere effect) and between chromosomes (crossover assurance) [2]. Because the mechanisms that generate crossover patterning have remained elusive for over a century, it has been difficult to assess the relationship between crossover patterning and meiotic chromosome behavior. We show here that meiotic crossover patterning is lost in Drosophila melanogaster mutants that lack the Bloom syndrome helicase. In the absence of interference and the centromere effect, crossovers are distributed more uniformly along chromosomes. Crossovers even occur on the small chromosome 4, which normally never has meiotic crossovers [3]. Regulated distribution of crossovers between chromosome pairs is also lost, resulting in an elevated frequency of homologs that do not receive a crossover, which in turn leads to elevated nondisjunction.

Keywords

bloom syndrome helicase
crossover patterning
meiosis
meiotic recombination
crossover interference
crossover assurance
centromere effect
nondisjunction
Drosophila

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