Telomeres in fungi

Abstract

Telomeres are the functional elements concluding and defining each linear chromosome in eukaryotes. They play an essential role in protecting genetic material and preventing genome loss during cell division. At the same time, and in stark contrast, they are remarkably dynamic regions: initial analyses of yeast genomes have shown, through comparative genomics, that regions close to telomeres are prone to rearrangements and duplication and thus are particularly variable between strains and species. This propensity for variation leads to the birth of new and alternative gene functions and helps to accelerate genome evolution and divergence. However, this special property, while making telomeric regions of even greater scientific interest, complicates investigation. Firstly, repetitive DNA is problematic to clone and sequence properly. Secondly, the reoccurring rearrangements and associated lack of synteny between the telomeric regions of even very closely related species creates daunting challenges for the comparative approach. This drives the development of special cloning and bioinformatic strategies. Such efforts should be fruitful, since a comparative approach of telomeres and subtelomeres promises many insights of significance to the research of ageing and cancer, chromosome dynamics in cell division, and the processes of evolution and speciation.

Rapid Expansion and Functional Divergence of Subtelomeric Gene Families in Yeasts

“…This 33kb region agrees with previous studies on the telomere position effect [5] and sequence similarity between nonhomologous chromosome ends [2,3]. For our analyses, we classified each gene as subtelomeric or non-subtelomeric based on its distance from the chromosome end.…”

“…A precise definition of a subtelomere is difficult because the length of the subtelomeric region varies from 20 kb in some yeasts to several hundred kb in higher eukaryotes [2,3]. Apart from the low gene density, subtelomeres are characterized by epigenetic silencing [4,5] and increased rates of recombination and mutation [3,6,7,8,9], with exception to flies [10,11].…”

“…Apart from the low gene density, subtelomeres are characterized by epigenetic silencing [4,5] and increased rates of recombination and mutation [3,6,7,8,9], with exception to flies [10,11]. These regions are often lacking from so-called “whole genome” sequences because their high repeat content and extensive sequence similarity [12] make it difficult to assemble these regions and to distinguish orthologs and paralogs [2,13,14]. As a result, subtelomeres remain relatively understudied.…”

Tay1 Protein, a Novel Telomere Binding Factor from Yarrowia lipolytica

“…Studies in yeasts, especially in Saccharomyces cerevisiae, Kluyveromyces lactis, Candida albicans, and Schizosaccharomyces pombe, have provided invaluable information about the maintenance and dynamics of nuclear telomeres (17). From these studies it is clear that, whereas some features of telomeres are general and carry over to higher eukaryotes, some telomere-associated components are specific for a given phylogenetic clade.…”

Naumovozyma castellii: an alternative model for budding yeast molecular biology

“…The phylogenomic data imply that the formation of the DAL cluster happened rather quickly through genomic rearrangements which brought together the genes into a single subtelomere. Intriguingly, subtelomeres are highly dynamic regions characterized by frequent duplication events and generation of novel genes, thus supplying the genomic plasticity giving the basis for adaptive opportunities (Cohn et al ., ; Snoek et al ., ). In addition, the subtelomeric location may efficiently provide for a coordinated expression of the novel clustered genes by epigenetic modifications.…”