BERKELEY, CA -- Sex is a boon to evolution; it allows genetic material from parents to recombine, giving rise to a unique new genome. But how did sex itself evolve" Researchers at the Department of Energy's Lawrence Berkeley National Laboratory and the University of California at Berkeley have found clues to one part of this complex question in ongoing studies of the nematode Caenorhabditis elegans.
Abby Dernburg, of Berkeley Lab's Life Sciences Division and UC Berkeley's Department of Molecular and Cell Biology, working with graduate student Carolyn Phillips, has identified a key family of genes and proteins that help bring C. elegans chromosomes together during meiosis. This specialized cell division produces gametes, or sex cells, each of which has only one copy of each chromosome instead of the two copies most cells carry.
During meiosis a cell replicates and then divides twice, resulting in sperm or eggs with just one set of chromosomes each. For meiosis to work properly, corresponding chromosomes must first identify each other, then line up accurately and stay together during the recombination process. Different organisms use different methods for these critical steps; in C. elegans, the job is initiated by regions called Pairing Centers, which are found near one end of each of the worm's six chromosome. Dernburg's lab has been studying the role of these special regions.
Last year Dernburg, Phillips, and their colleagues identified the function of a C. elegans protein called HIM-8. This protein binds to and helps bring together copies of the worm's sex chromosome (the X chromosome) to achieve stable pairing, called synapsis. Now Dernburg and Phillips have found three new genes, which they have named zim-1, zim-2, and zim-3, that perform the same functions for the worm's five additional chromosomes. Their results are published in the December issue of Developmental Cell.