A dicentric chromosome of Drosophila melanogaster showing alternate centromere inactivation

Abstract.

Dicentric chromosomes are rarely found, because they interfere with normal cell division causing chromosome instability. By in situ hybridization of region-specific heterochromatic yeast artificial chromosomes we have found that the artificially generated C(1)A chromosome of Drosophila melanogaster has two potential centromeres: one carries all the sequences of the centromere of the Y chromosome and the other carries only a part of the Y centromeric region that is rich in telomere-related sequences. Immunostaining with anti-Bub1 (a kinetochore-specific marker) shows that, in spite of the differences in sequence, both centromeres can be active although as a rule only one at a time. In a small fraction of the chromosomes centromere inactivation is incomplete, giving rise to true dicentric chromosomes. The centromere inactivation is clonally inherited, providing a new example of epigenetic chromosome imprinting and the possibility of genetically dissecting this process. The involvement of telomere-related sequences in centromere function is discussed.