Telomere length regulation--a view from the individual chromosome perspective.

Telomeres are specialized structures at chromosome termini implicated in oncogenesis and cellular aging. Since both phenomena are related to variations in telomere length it is of interest to understand mechanisms responsible for telomere length regulation. Recent studies in mammalian cells indicate that specific chromosomes may have specific telomere lengths, suggesting the existence of chromosome-specific factors involved in telomere length regulation. Although these chromosome-specific factors are largely unknown at present, in the mouse evidence suggests a possible role of centromere position in telomere length regulation-telomeres closer to centromeres (i.e., p-arm telomeres) are significantly shorter than their counterparts more distant from centromeres (i.e., q-arm telomeres). The mouse may be a special case because its karyotype consists almost exclusively of acrocentric chromosomes in which p-arm telomeres and centromeres are located immediately adjacent to each other. However, a weak correlation between telomere length and centromere position is observed in the case of nonacrocentric human and Chinese hamster chromosomes, suggesting that the putative centromere position effect might be evolutionarily conserved. Alternatively, telomere length in individual nonacrocentric chromosomes may be affected by the sequence organization of subtelomeric chromosome regions or by some other, currently unknown, factors.