Directed motion of telomeres in the formation of the meiotic bouquet revealed by time course and simulation analysis.

Chromosome movement is critical for homologous chromosome pairing during meiosis. A prominent and nearly universal meiotic chromosome reorganization is the formation of the bouquet, characterized by the close clustering of chromosome ends at the nuclear envelope. We have used a novel method of in vitro culture of rye anthers combined with fluorescent in situ hybridization (FISH) detection of telomeres to quantitatively study bouquet formation. The three-dimensional distribution of telomeres over time was used to obtain a quantitative profile of bouquet formation intermediates. The bouquet formed through a gradual, continuous tightening of telomeres over approximately 6 h. To determine whether the motion of chromosomes was random or directed, we developed a computer simulation of bouquet formation to compare with our observations. We varied the diffusion rate of telomeres and the amount of directional bias in telomere movement. In our models, the bouquet was formed in a manner comparable to what we observed in cultured meiocytes only when the movement of telomeres was actively directed toward the bouquet site, whereas a wide range of diffusion rates were permitted. Directed motion, as opposed to random diffusion, was required to reproduce our observations, implying that an active process moves chromosomes to cause telomere clustering.