"Once they've identified each other at some place, they'll begin the process we call synapsis, which involves building this beautiful structurethe synaptonemal complexand using it to form an intimate association that runs the entire length of each pair of chromosomes," Hawley explains.
Some model organisms employed in the study of meiosis, such as yeast and the roundworm Caenorhabditis elegans, use the ends of their chromosomes to facilitate the process. "These organisms gather all the chromosome ends against the nuclear envelope into one big cluster called a bouquet or into a bunch of smaller clusters called aggregates, and this brings the chromosome ends into proximity with each other," Hawley says. "This changes the problem of finding your homologue in this great big nucleus into one of finding your mate on just the surface of the inside of the nucleus."
But the fruit fly Drosophila melanogasterthe model organism in which meiosis has been thoroughly studied for more than a century, and which Hawley has studied for almost 40 years has unusual chromosome ends that don't lend themselves to the same kind of clustering.
"So even though the study of meiosis began in Drosophila, we really haven't had any idea how chromosomes initiate synapsis in Drosophila," Hawley says. "Now, we show that instead of clustering their chromosome ends, flies cluster their centromereshighly organized structures that chromosomes use to move during cell division. From there, the biology works pretty much as you would expect: synapsis is initiated at the centromeres, and it appears to spread out along the arms of the chromosomes."
The ramifications of the findings extend beyond fruit flies, as there's some evidence that synapsis starts at centromeres in other organisms. In addition, Hawley and coauthors found that centromere clustering may
|Contact: Gina Kirchweger|
Stowers Institute for Medical Research