During meiosis, the reductional segregation of homologous chromosomes at the first meiotic division requires reciprocal exchange (crossing over) between homologs1. The number of crossovers is tightly regulated (one to two per homolog in mice2), and their distribution in the genome is not random—recombination 'hot' and 'cold' regions can be identified3,
4. We developed a molecular assay to study these events directly in mouse germ cells. This analysis was developed with reference to the proteosome subunit type 9 (Psmb9, previously called Lmp2) hot-spot region identified through genetic analysis5,
6. Here we show that this hot spot is an initiation site of meiotic recombination on the basis of two observations: (i) crossover density is maximal in an interval of 210 bp and decreases on both sides of this region; (ii) a high frequency of gene conversion is found in the region of highest crossover density. We then used this strategy to carry out the first temporal analysis of meiotic recombination in mouse spermatogenesis and demonstrate that crossover events occur during the pachytene stage of meiotic prophase.
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type 9 (Psmb9, previously called Lmp2) hot-spot region identified through genetic analysis
gene
