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

The spindle-assembly checkpoint ensures that, during mitosis and meiosis, c hromosomes do not segregate until they are properly attached to the microtu bules of the spindle. Here we show that mdf-l and mdf-2 are components of t he spindle-assembly checkpoint in Caenorhabditis elegans, and are essential for the long-term survival and fertility of this organism. Loss of functio n of either of these genes leads to the accumulation of a variety of defect s, including chromosome abnormalities, X-chromosome non-disjunction or loss , problems in gonad development, and embryonic lethality. Antibodies that r ecognize the MDF-2 protein localize to nuclei of the cleaving embryo in a c ell-cycle-dependent manner. mdf-l, a gene encoding a product that interacts with MDF-2, is required for cell-cycle arrest and proper chromosome segreg ation in premeiotic germ cells treated with nocodoazole, a microtubule-depo lymerizing agent. In the absence of mdf gene products, errors in chromosome segregation arise and accumulate, ultimately leading to genetic lethality.