Cytological and functional aspects of telomere maintenance

The fact that eukaryotic chromosomes are linear poses a special problem for their maintenance: the natural ends of chromosomes must be distinguished f rom ends generated by chromosomal breakage and somehow, the chromosome ends must also be fully replicated to maintain their integrity. Telomeres, the complex structures at the ends of chromosomes are thought to be instrumenta l for both of these functions. However, recent insights in telomere biology suggest that these terminal structures do much more than just fulfill thes e two basic functions. Cytological data demonstrate that telomeres may play leading roles in chromatin organization and nuclear architecture during mi tosis and meiosis. Moreover, non-functional telomeres may lead to genetic i nstability, a common prelude to cancer. Here, we review the basic functions of telomeres during chromosome replication and discuss the cytological asp ects of telomere function during mitosis and meiosis.