Synapsis and chiasma formation in Caenorhabditis elegans require HIM-3, a meiotic chromosome core component that functions in chromosome segregation
Abstract
Meiotic chromosomes are organized about a proteinaceous core that forms between replicated sister chromatids. We have isolated aCaenorhabditis elegans gene, him-3, which encodes a meiosis-specific component of chromosome cores with some similarity to the yeast lateral element protein Hop1p. Antibodies raised against HIM-3 localize the protein to condensing chromosomes in early prophase I and to the cores of both synapsed and desynapsed chromosomes. In RNA interference experiments, chromosomes appear to condense normally in the absence of detectable protein but fail to synapse and form chiasmata, indicating that HIM-3 is essential for these processes. Hypomorphs of him-3, although being synapsis proficient, show severe reductions in the frequency of crossing-over, demonstrating that HIM-3 has a role in establishing normal levels of interhomolog exchange. Him-3 mutants also show defects in meiotic chromosome segregation and the persistence of the protein at the chromosome core until the metaphase I–anaphase I transition suggests that HIM-3 may play a role in sister chromatid cohesion. The analysis of him-3provides the first functional description of a chromosome core component in a multicellular organism and suggests that a mechanistic link exists between the early meiotic events of synapsis and recombination, and later events such as segregation.
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Footnotes
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↵Corresponding author. Present address: Section of Molecular and Cellular Biology, Division of Biological Sciences, University of California, Davis, California 95616-8535 USA.
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E-MAIL mczetka{at}ucdavis.edu; FAX (530) 752-1185.
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- Received April 12, 1999.
- Accepted July 19, 1999.
- Cold Spring Harbor Laboratory Press