HIM-10 is required for kinetochore structure and function on Caenorhabditis elegans holocentric chromosomes

Macromolecular structures called kinetochores attach and move chromosomes w ithin the spindle during chromosome segregation. Using electron microscopy, we identified a structure on the holocentric mitotic and meiotic chromosom es of Caenorhabditis elegans that resembles the mammalian kinetochore. This structure faces the poles on mitotic chromosomes but encircles meiotic chr omosomes. Worm kinetochores require the evolutionarily conserved HIM-10 pro tein for their structure and function. HIM-10 localizes to the kinetochores and mediates attachment of chromosomes to the spindle. Depletion of HIM-10 disrupts kinetochore structure, causes a failure of bipolar spindle attach ment, and results in chromosome nondisjunction. HIM-10 is related to the Nu f2 kinetochore proteins conserved from yeast to humans. Thus, the extended kinetochores characteristic of C. elegans holocentric chromosomes provide a guide to the structure, molecular architecture, and function of convention al kinetochores.