Saccharomyces castellii: A new model organism for telomere research

Abstract

Telomeres are natural ends of eukaryotic chromosomes and perform a major role in cell biology. They protect chromosomes from degradation, fusions and the end replication problem. To study telomeres different model organisms are used including a number of yeast species. In this work I present a new species in yeast telomere studies – Saccharomyces castellii. This yeast exhibits a lot of interesting features that makes this species one of the most promising models for future telomere research. Thus, this work was focused on developing and optimization of genetic assays and tools to make telomere research possible in S. castellii.

We analyzed a number of basic tools and assays that are already used for Saccharomyces cerevisiae research and found that these tools can be directly applied to study S. castellii genetics. Furthermore, using our newly developed assays we analyzed the structure and properties of S. castellii telomeric 3’ overhangs and found that S. castellii exhibits not only short but also a fraction of long 3’ overhangs.

In summary, we found that S. castellii is a new promising model organism for different studies and especially for telomere biology.

• author: Astromskas, Eimantas
• supervisor: Marita Cohn
• opponent: McEachern, Michael, Associate Professor
• organization: Department of Biology
• publishing date: 2008
• type: Thesis
• publication status: published
• subject: Biological Sciences
• keywords: Naumovia castellii, Saccharomyces castellii, yeast, genetic tools, gene targeting, telomere, CDC13., telomeric overhang
• pages: 112 pages
• defense location: Sölvegatan 35, Lund
• defense date: 2008-10-08 10:00:00
• ISBN: 978-91-85067-47-3
• language: English
• LU publication?: yes
• additional info: A popular scientific summary. Eukaryotic cells store their genetic material encoded in DNA molecules. Because of the vast amount of information stored these DNA molecules becomes extremely larger in more complex organisms like humans. To minimize the size of the DNA molecules, they are folded by proteins in a special structure called chromosomes. Even though the main function of chromosomes is to store the genetic information, this information must be copied for a new generation of the cell and the genes must be accessible for transcription (executing functions of the genes). To perform these roles number of proteins helps binds to chromosomes. Interestingly, while most of the chromosome is bound by a conserved complex called nucleosome, the very end of chromosome is very different. These ends contain no genetic information and consist only of repeated DNA sequences. These sequences are called telomeres and perform a vital role of chromosome stability. Because of a sophisticated mechanism of DNA replication (i.e. making a new DNA copy), a new linear DNA molecule become shorter and shorter after each replication round. Bacteria have no problem because they have circular chromosomes, but eukaryotes (i.e. human, mouse, plants) have linear chromosomes and they solve this problem with a help of telomeres and a special enzyme called telomerase, which elongates short telomeres. Usually telomeres are built up of thousands of similar DNA sequence repeats, covered by different proteins, and their main function is to protect chromosome ends. Also they are very important in the regulation of cell division. After discovery that chromosomes cannot be fully replicated, a new interesting mechanism of aging was suggested. Each cell can divide only for a limited number of times and than telomeres are destroyed leaving chromosome ends unprotected and genes near telomere are damaged as well and these make cell to die. This mechanism looks very promising in avoiding cancer: the cell cannot divide indefinitely, so cancer cells also supposed to die after this limit is exhausted. But, as mentioned before, the telomerase enzyme is able to deal with this problem and to prolong telomeres as well as cell division number. Normally telomerase can be detected in such organisms as single cellular yeast and protozoans. They need to maintain a stable length of their telomeres and to pass it to the next generations. But multicellular organisms (such as human) pass only germ line cells, so only these cells have to maintain their telomeres at the stable length. All other cells have to die sooner or later. Despite the fact that telomerase gene is in every cell, it works only in germ line cells, while other cells have no or very little activity of this enzyme. In contrast, cancer cells have to divide unlimited number of times, so very often these cells activate telomerase gene (85 – 90 % of all cancer has this gene activated) and become immortal. These discoveries led to suggestion that inactivating telomerase can cure most of the cancer types. Also by activating it in some cells can solve the aging problem. Those ideas made telomerase a very interesting target to investigate. Despite a great promise of telomerase in cancer treatment, the actual mechanism of telomerase regulation is still poorly understood. Interestingly, the mechanisms regulating telomerase and telomere elongation are very similar in different organisms. This similarity allows researchers to use different organisms to get a full picture of the complex nature of telomere biology. Here, yeast is one of the most powerful eukaryotic research organisms to date. Because of the fast growth, easy genetic manipulation and long years of work this organism became the most studied eukaryotic cell to date. In particular, baker’s yeast (Saccharomyces cerevisiae) is mostly used in research. Despite all advantages of S. cerevisiae, this species was found to be quite different from other organisms in their telomere sequences and telomerase activity. These differences cause problems when trying to correlate results obtained from other species and studying different aspects of telomere biology. Thus, our group started to investigate another yeast species – Saccharomyces castellii. Interestingly, a lot of features of telomere biology of this yeast are closer to human than other yeast. Unfortunately, this species was never used intensively for any research. Thus, my aim in this study was to create different genetic tools that allow investigation of this yeast genetics and also start investigating telomere biology in this species. The information about affiliations in this record was updated in December 2015. The record was previously connected to the following departments: Department of Cell and Organism Biology (Closed 2011.) (011002100)
• id: ecf960d5-3502-4410-825f-7bf0f57f17ab (old id 1233223)
• date added to LUP: 2016-04-04 14:27:11
• date last changed: 2018-11-21 21:20:24