The relationship of meiotic checkpoint regulation, synapsis, and crossing over in Drosophila melanogaster

Proper chromosome segregation is achieved through three important meiotic events. The first is synapsis, where a proteinaceous structure, the synaptonemal complex (SC), forms between homologous chromosomes and juxtaposes them together. Then, recombination, which is initiated by programmed double strand breaks (DSBs) introduced into DNA that leads to a crossover event. Chiasmata, which are physical markers of where an exact exchange of genetic material occurred between homologous chromosomes during crossing over, are important to maintain the genetic integrity and variability of offspring. Zip3, a conserved meiotic protein found in budding yeast to humans, has been found to be required for crossing over. Furthermore, previous studies in budding yeast (Zip3) and C. elegans (ZHP-3) have shown the homologs to be crossover markers. However, the exact mechanism as to how Zip3 combines synapsis and recombination to promote crossing over is unknown. In Drosophila melanogaster, there are two homologs of Zip3, Zip3 related protein on the third and X chromosome (Z3rp3 and Z3rpX). Because Drosophila currently does not have a way to visualize crossovers, this study involves determining the function of Z3rp3 and Z3rpX during meiotic recombination and if they are crossover markers. HA-tagged transgenes were constructed to express the protein of each homolog. Z3rp3 HA and Z3rpX HA transgenes revealed an abnormal localization pattern, resulting in them not being good crossover markers. However, the transgenes displayed dominant negative effects on meiosis, indicating they had another important function on the process. Loss of function mutants created in z3rp3 and z3rpX showed that they not only had separate functions on the events of meiosis leading to proper chromosome segregation, but also that they seemed to be redundant, since the z3rpX z3rp3 double mutant exhibited the most severe phenotypes on synapsis, recombination, and crossing over. Overall, z3rp may be playing similar roles in the communication between SC formation and recombination events as in budding yeast and C. elegans, but in different contexts. Thus, I have results that provide new insights into the functional features of z3rp in Drosophila that confirms its role in crossing over.M.S.Includes bibliographical referencesIncludes vitaby Sanese Kania White-Brow