Physical basis for long-distance communication along meiotic chromosomes (ChIP-chip))

Viable gamete formation requires segregation of homologous chromosomes connected, in most species, by crossovers. DNA double-strand break (DSB) formation and the resulting crossovers are regulated at multiple levels to prevent overabundance along chromosomes. Meiotic cells coordinate these events between distant sites, but the physical basis of long-distance chromosomal communication has been unknown. We show that DSB hotspots up to ~200 kb (~35 cM) apart form clusters via hotspot-binding proteins Rec25 and Rec27 in fission yeast.  Clustering coincides with hotspot competition and interference over similar distances. Without Tel1 (ATM tumor-suppressor homolog), DSB and crossover interference become negative, reflecting coordinated action along a chromosome. These results indicate that DSB hotspots within a limited chromosomal region and bound by their protein determinants form a clustered structure that, via Tel1, allows only one DSB per region. Such a “roulette” process among clusters explains the observed pattern of crossover interference in fission yeast. Key structural and regulatory components of clusters are phylogenetically conserved, suggesting conservation of this vital regulation. Based on these observations, we discuss variations on a model in which clustering and competition between DSB sites leads to DSB interference and in turn produces crossover interference. Meiotic DSBs (Rec12-DNA linkages) assayed in two strains that differ at two hotspots: one strain has the ade6-3049 hotspot but lacks mbs1, while the other has the ade6-3057 non-hotspot allele but has mbs1.