Research profile
1. Telomeres and telomerases - molecular analysis and evolution
The ends of eukaryotic chromosomes "telomeres" are nucleoprotein structures that protect chromosomes from degradation and fusions. Many organisms use telomerase, comprising telomere reverse transcriptase (TERT) and telomerase RNA (TR), to re-synthesize terminal chromosomal DNA lost during DNA replication. We discovered in
Asparagales that species divergence is associated with the evolution of novel types of telomeres. In addition to group (i) plants (e.g. orchids) with typical plant telomeres based on (TTTAGGG)n motifs, the group (ii) plants (e.g. Asparagus) exists. These plants have mutation(s) that results in the synthesis of a human-type of telomere motif (TTAGGG)n. The last group (iii) plants (e.g.
Allium, onion) do not synthesize any known telomeric repeat and must have substantial changes in their telomere-maintenance machinery. The variations that occur in these related plants enable us to address strategic questions about telomere and telomerase evolution and function of individual components of telomeric machinery.
The DNA and protein components of telomeres should be regarded as with any other chromosome elements as evolving and co-evolving over time and responding to changes in the genome and to environmental stresses. We aim to analyse the influence of changing DNA sequence motifs on the properties of the telomere cap.
Did individual telomere-binding proteins align themselves to the change in DNA sequence, or were they rather replaced by other proteins with newly acquired function? What were molecular causes of the switches in telomere sequence synthesis ? can we trace them at the level telomerase genes?
Specific objectives of the project include (1) isolation and comparative analysis of telomerase genes from species of Asparagales including species that synthesise ?typical? plant and human types of telomere; (2) analysis of DNA-protein and protein-protein interactions of candidate telomere-binding proteins and localisation of these proteins
in situ and in vivo; (3) comparative analysis of chromatin structure of typical and alternative telomeres; (4) role of telomere structure and organisation in association with development and cellular differentiation including cellular polyploidy and apoptosis.
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Cover Illustration: Fluorescence in situ hybridization in a root tip metaphase squash of Nothoscordum striatum (Alliaceae) probed with concatemers of the human-type telomere motif (TTAGGG)n (biotin-labeled probe detected with cy3 avidin, red fluorescence; DAPI counterstain for DNA, blue fluorescence). The (TTAGGG)n minisatellite motif is found at chromosome ends (the telomeres). The authors showed that these motifs, and all investigated minisatellite repeats typical of eukaryote telomeres, are lost with the divergence of the genus Alllium from the rest of Alliaceae.
See Sykorova et al.: Minisatellite telomeres occur in the family Alliaceae but are lost in Allium, pp. 814-823, in this issue (Am. J. Bot. 93(6), 2006). Photo credit: Kar Yoong Lim.
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2. Applications of telomere biology in medicine and biotechnology
Telomerase activity is closely connected to problems of cellular immortality, proliferative
capacity, differentiation, cancer and aging. In humans, telomerase activity is restricted to the germ-line, cancer, and possibly cycling stem cells of self-renewing tissues. It has been shown that functioning telomere maintenance is a necessary factor of cellular immortalisation. The ability to bypass senescence by circumventing telomere-based growth limitations is thought to be a critical step in the progression to malignancy. Today's telomere research advanced from purely descriptive approach to promising applications in medicine. These applications include "passive" ones, among which the use of analysis of telomeres and telomerase for cancer diagnostics is the best known. The "active" applications involve targeted down- or up-regulation of telomere synthesis, either to mortalise immortal cancer cells or to re-juvenate mortal somatic cells and tissues for cellular transplantations, respectively. Moreover, genetically engineered stable telomerase expression makes it possible to establish immortal cell lines without their neoplastic transformation. These cells may be useful for research and biotechnology purposes.
Our collaborative research with medical institutions is focused on biomedicine of telomeres.
