Abstract
During meiosis, chromosomes pair with their homologous partners, and a structure known as the synaptonemal complex (SC) assembles between them. Evidence indicates that this material plays a role in regulating crossover recombination between homologs, although this remains controversial. Here we use three-dimensional STochastic Optical Reconstruction Microscopy (3D-STORM) to interrogate the molecular architecture of the SC in intact germline tissue from Caenorhabditis elegans, and analyze its ultrastructure during meiotic progression. Using a probabilistic mapping approach, we determine the position and orientation of the four known SC structural proteins. We report that a marked structural transition occurs within this material upon crossover designation. We also identify a mutation that disturbs both SC ultrastructure and crossover interference, the widespread mechanism that results in non-randomly wide spacing of crossovers between the same chromosome pair. Together with other evidence, our findings suggest that the SC is an active material, and that structural transitions may directly contribute to chromosome-wide crossover regulation.