Investigating the effect of Mei-218 Phosphorylation on Interference and Crossover Rates in Drosophila melanogaster

Meiotic crossovers are strategically distributed along chromosomes during meiosis I to promote proper disjunction of homologous chromosomes and genetic diversity. Crossover interference is a type of patterning where one crossover prevents crossovers from occurring in close proximity to promote proper segregation of chromosomes. It is known that the phosphoprotein product of the dicistronic mei-217/mei-218 gene, mei-218, is part of a multi protein complex that promotes crossovers in Drosophila melanogaster, but it remains unknown which regions of the mei-218 are responsible for this. Previous research has indicated that D. mauritiana evolved to have higher crossover rates than D. melanogaster. We investigated the effect of phosphorylation of mei-218 on interference and crossover rates in Drosophila melanogaster. We also looked into whether specific sequences of mei-218 in Drosophila mauritiana were responsible for the higher recombination rates. Specific serine and threonine sites in mei-218 were changed to aspartic acid to mimic phosphorylation in D. melanogaster. To prevent phosphorylation, the same serine and threonine sites were changed to alanine. We replaced four regions of D. melanogaster mei-218 with D. mauritiana mei-218 to investigate whether these regions were responsible for such higher crossover rates. X chromosome nondisjunction and 2L chromosome crossover interference assays were performed. D. melanogaster with eight mei-218 sites changed that inhibited phosphorylation had a significant decrease in crossover and interference, while nondisjunction rates increased relative to the wild type fly. D. melanogaster with phosphomimetic mei-218 also had increased nondisjunction. These results indicate that phosphorylation of specific amino acids in mei-218 plays a key role in allowing proper crossover processes to occur. More crossover interference assays will be done changing only three to five amino acids to narrow down which, if not all, of the previously examined eight sites of mei-218 get phosphorylated for successful disjunction and crossover processes. As expected, D. melanogaster that had regions of mei-218 replaced with that of D. mauritina mei-218 showed no significant difference in nondisjunction rates. Crossover interference must be assayed to find whether the mei-218 differences between D. melanogaster and D. mauritiana are responsible for D. mauritiana having nearly twice as many crossovers as D. melanogaster.