The recombination landscape of Drosophila melanogaster can be repatterned by a single gene
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Meiotic recombination plays an important role in ensuring proper chromosome segregation during meiosis I through the creation of chiasmata that connect homologous chromosomes. Recombination plays an additional role in evolution by creating new allelic combinations. Organisms display species-specific crossover patterns, but how these patterns are established is poorly understood. Drosophila mauritana displays a differing recombination pattern compared to Drosophila melanogaster , with D. mauritiana experiencing a reduced centromere effect, the suppression of recombination emanating from the centromeres. To evaluate the contribution of the synaptonemal complex (SC) C(3)G protein to these recombination rate differences, the D. melanogaster allele was replaced with D. mauritiana c(3)G coding sequence. We found that the D. mauritiana C(3)G could interact with the D. melanogaster SC machinery to build full length tripartite SC and chromosomes segregated accurately, indicating sufficient crossovers were generated. However, the placement of crossovers was altered, displaying an increase in frequency of the centromere-proximal euchromatin indicating a decrease in the centromere effect similar to that observed in D. mauritiana . Recovery of chromatids with more than one crossover was also increased, likely due to the larger chromosome span now available for crossovers. As replacement of a single gene mediated a strong shift of one species’ crossover pattern towards another species, it indicates a small number of discrete factors may have major influence on species-specific crossover patterning. Additionally, it demonstrates the SC, a structure known to be required for crossover formation in many species, is likely one of these discrete factors.
Lay Abstract
Meiotic crossovers are important for ensuring proper chromosome segregation and generating genetic diversity. Different species display unique crossover patterns but the mechanisms that establish these patterns are poorly understood. The synaptonemal complex (SC) is built between meiotic chromosomes and promotes crossover formation. Replacement of the SC gene c(3)G in the fruit fly Drosophila melanogaster with Drosophila mauritiana c(3)G resulted in full-length SC assembly and proper chromosome segregation, but the D. melanogaster crossover pattern was shifted to appear more similar to D. mauritiana . This demonstrates that crossover patterning can be largely influenced by minor changes in the makeup of the SC.
