Centromeres and Telomeres
Emma L. Northrop and Lee H. Wong
from: Epigenetics: A Reference Manual (Edited by: Jeffrey M. Craig and Nicholas C. Wong). Caister Academic Press, U.K. (2011)
In eukaryotes, each chromosome has one centromere and its ends are protected by telomeres. The centromere is a specialized chromosomal locus that directs kinetochore assembly and provides the site for microtubule attachment, allowing accurate chromosome segregation during cell division. Despite the critical role centromeres play, centromeric DNA sequences are highly variable and not conserved between species. Increasing evidence, including the discovery of functional neocentromeres, suggests that centromere identity and function is epigenetically defined through the formation of a specialised chromatin structure. This chapter reviews recent studies addressing the structural and functional characterisation of centromere chromatin, its assembly and propagation during cell division. Telomeres are specialized nucleoprotein complexes that protect the chromosome ends from degradation. In recent years, it has become increasingly clear that heterochromatic marks at telomeres act as negative epigenetic regulators of telomere elongation, repress recombination events at the telomere and are critical for maintaining telomere structural integrity. Recent research reporting telomeres being transcribed by RNA polymerase II to give rise to TERRA RNA, open up an additional level of regulation at the telomere. This chapter will discuss the links between the epigenetic status of telomeres, telomere function and telomere-length regulation, and the implications on cellular reprogramming, aging and cancer read more ...