Components of the spindle-assembly checkpoint are essential in Caenorhabditis elegans.

The spindle-assembly checkpoint ensures that, during mitosis and meiosis, chromosomes do not segregate until they are properly attached to the microtubules of the spindle. Here we show that mdf-1 and mdf-2 are components of the spindle-assembly checkpoint in Caenorhabditis elegans, and are essential for the long-term survival and fertility of this organism. Loss of function of either of these genes leads to the accumulation of a variety of defects, including chromosome abnormalities, X-chromosome non-disjunction or loss, problems in gonad development, and embryonic lethality. Antibodies that recognize the MDF-2 protein localize to nuclei of the cleaving embryo in a cell-cycle-dependent manner. mdf-1, a gene encoding a product that interacts with MDF-2, is required for cell-cycle arrest and proper chromosome segregation in premeiotic germ cells treated with nocodazole, a microtubule-depolymerizing agent. In the absence of mdf gene products, errors in chromosome segregation arise and accumulate, ultimately leading to genetic lethality.