Centromere on the Move
- The Murdoch Childrens Research Institute, Royal Children's Hospital, Melbourne 3052, Australia
This extract was created in the absence of an abstract.
The centromeres of primate chromosomes are composed of complex arrays of alphoid sequences that are organized from tandemly repeating units of 171 bp. The ubiquity of alphoid DNA at the centromeric regions suggests a preference for repetitive DNA in the assembly of the kinetochore. Nevertheless, recent analyses of ectopic centromeres (neocentromeres) at non-alphoid-containing chromosomal sites suggest that centromeres can be “repositioned” along a chromosome through a still poorly understood epigenetic mechanism of “activation” of hitherto noncentromeric genomic DNA (Choo 1997). In this issue, Ventura et al. (2001) present evidence for centromere repositioning along the X chromosome during primate evolution that raises interesting mechanistic possibilities.
Centromere Repositioning Via Neocentromere Emergence?
The study of Ventura et al. (2001) is based on comparison of the conservation of DNA sequences on the X chromosomes of humans and two of the Lemuridae: the black lemur and the ringtailed lemur. Lemurs are small primates related to the monkey and are found mainly in Madagascar. Unlike the submetacentric human X chromosome, the black and ringtailed lemur chromosomes are telocentric and metacentric, respectively. Ventura et al. have performed FISH analysis on the lemur X chromosomes using human chromosomal paints and a panel of BACs/cosmids spanning the entire X chromosome. Based on the relative map positions of these probes, they conclude that the lemur X chromosomes are isosequential to the human X chromosome (Fig.1). They then propose that neocentromere activation may account for the centromere repositioning that has given rise to the acrocentric, metacentric, and submetacentric configurations in the three different species (Fig. 2). Because the corresponding chromosomal regions at which the neocentromeres putatively originated do not contain the large arrays of repetitive sequences that are now found at the repositioned centromeres, Ventura et al. suggest that heterochromatic materials may have gradually accumulated at the neocentromere sites. In addition, the investigators indicate that …
