X-chromosome Meiosis in C. Elegans

Haverford College, Haverford PA

Investigators

Abstract

Meiosis is the process by which eukaryotic organisms reduce their chromosome number in half during the formation of gametes. Early in meiosis, homologous chromosomes pair, exchange, and synapse along their length. Both the number and the location of exchanges are highly regulated, a phenomenon known as crossover control. Crossover control is thought to be related to changes in chromosome structure, but this has not been proved. The mechanism of pairing itself, the process by which one chromosome finds its homologous partner, is also not understood. This research will address both of these issues in the model organism Caenorhabditis elegans. Mutations in the gene him-5 affect crossover control, most strongly on the X chromosome but also on the other chromosomes. HIM-5 is a germline-specific chromosomal protein that interacts with twelve other proteins, all of them either chromosomal proteins or expressed in the germline. The functions and localization of these twelve proteins will be investigated in both wild-type and him-5 mutant animals. In addition, suppressors of him-5 will be identified genetically and compared to the protein interactions. Suppressors will include a broader class of genes that those involved in the protein interactions, and these genes will also be mapped, cloned, and analyzed. Mutations in the gene him-8 in C. elegans specifically abolish pairing of the X chromosome with no effect on other chromosomes. The HIM-8 protein mediates pairing by binding to specific sequences at the pairing center on the X chromosome. Proteins related to HIM-8 have been shown to mediate paring of each of the autosomes, also by binding to specific pairing centers on these chromosomes. It is postulated that HIM-8 and these other proteins work as the targeting subunit of a larger protein complex that bring chromosomes together. Proteins that interact with HIM-8 and its relatives will be found by testing nearly every protein in the worm genome with the yeast two-hybrid assay. Interacting genes identified in this assay are already cloned, and information about their structure, expression, and possible function is available from genomic resources. The network of protein interactions will be connected to the existing broader network of protein interactions being done in C. elegans to find potentially all of the proteins that affect meiotic chromosome pairing. Several of these interacting proteins will be pursued further to analyze their effect on meiotic chromosome behavior. Mutational analysis of the him-8 gene will be used to determine functional domains of the protein and its interacting partners. All of these experiments will be done by undergraduate students working with the principal investigator. Because meiosis is a fundamental process whose main characteristics have been known for decades, most students are familiar with its basic properties. Therefore, the students will be carrying out significant research on a fundamental and familiar process.