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Classes of DNA associated with telomeres in the chironomids C. pallidivittatus and C. tentans

Kamnert, Iréne LU (1997)
Abstract
Telomeres in Chironomus consist of long complex tandem DNA repeats, which in C. pallidivittatus have been shown to extend to the extreme end of chromosomes. In C. pallidivittatus the telomeric repeats are present in large blocks, 50-200kb in size, most of them belonging to four major subfamilies. The main issue of this thesis has been to elucidate possible functional roles for these different subfamilies of telomeric repeats. Therefore, both intra- and intertelomeric mapping of the subfamilies were performed. One subfamily was found always to be located distally to the others, and have properties that could indicate a role in the protection of the chromosome ends. The subfamily identity of the most proximally situated repeat was identified... (More)
Telomeres in Chironomus consist of long complex tandem DNA repeats, which in C. pallidivittatus have been shown to extend to the extreme end of chromosomes. In C. pallidivittatus the telomeric repeats are present in large blocks, 50-200kb in size, most of them belonging to four major subfamilies. The main issue of this thesis has been to elucidate possible functional roles for these different subfamilies of telomeric repeats. Therefore, both intra- and intertelomeric mapping of the subfamilies were performed. One subfamily was found always to be located distally to the others, and have properties that could indicate a role in the protection of the chromosome ends. The subfamily identity of the most proximally situated repeat was identified in five of the seven non-telocentric chromosome ends. The junction between telomeric repeats and subterminal sequences was also characterized. In this region species and junction specific mutations were found, which were highly conserved between different chromosome ends within the same species. The homogenization pattern of these mutations indicated that gene conversion can act also between heterologous telomeres. The telomeric repeats exhibit a remarkable efficient homogenization whether they are located in the same or in different non-homologous chromosomes, an unusual feature since intrachromosomal homogenization usually are more efficient than homogenization between heterologues. Results from several earlier investigations had suggested transcriptional activity in the telomeric repeats in Chironomus. This issue was now addressed both in relation to possible roles for the different subfamilies in this transcription, and if this could be a connection to a process active in the elongation of the telomeres. (Less)
Abstract (Swedish)
Popular Abstract in Swedish

Hur slutar det? Är inte detta en fråga vi ofta vill ha besvarad? Så är åtminstone fallet i min avhandling, närmre bestämt gäller det här slutet på kromosomerna, de så kallade telomererna. Telomerer definieras som den DNA/proteinstruktur som avslutar linjära kromosomer. Gener återfinns ej i denna region vilken dock har andra viktiga funktioner. Kromosomer utan telomerer är instabila och fuserar lätt med varandra och kan också angripas av nedbrytande nukleaser. Ytterligare en viktig funktion är att förhindra att kromosomerna ”krymper”. Vem blir inte ledsen om sockarna i storlek 40 som stoppades in i tvättmaskinen snarare är storlek 36 då de tas ut efter tvätt? Vid varje replikering (=duplicering)... (More)
Popular Abstract in Swedish

Hur slutar det? Är inte detta en fråga vi ofta vill ha besvarad? Så är åtminstone fallet i min avhandling, närmre bestämt gäller det här slutet på kromosomerna, de så kallade telomererna. Telomerer definieras som den DNA/proteinstruktur som avslutar linjära kromosomer. Gener återfinns ej i denna region vilken dock har andra viktiga funktioner. Kromosomer utan telomerer är instabila och fuserar lätt med varandra och kan också angripas av nedbrytande nukleaser. Ytterligare en viktig funktion är att förhindra att kromosomerna ”krymper”. Vem blir inte ledsen om sockarna i storlek 40 som stoppades in i tvättmaskinen snarare är storlek 36 då de tas ut efter tvätt? Vid varje replikering (=duplicering) kopierar det normala replikeringsmaskineriet kromosomerna men detta har ej förmåga att duplicera den yttersta delen av kromosomen, vilket leder till en kopia som är kortare än sin mall. De flesta organismer, från ciliater till människa, har löst problemet genom telomerer bestående av korta DNA-sekvenser upprepade i tandem (=direkt efter varandra), vilka syntetiseras av ett speciellt enzym, telomeras. Undantag från denna lösning finns dock, ett exempel är den väl studerade modellorganismen bananflugan Drosophila melanogaster hos vilken kromosomerna förlängs med hjälp av speciella transposoner. Transposoner är så kallade ”hoppande element” vilka kan sätta in sig själva, eller en kopia av sig själva, på en ny plats i genomet.



Fjädermyggan Chironomus, som studerats i denna avhandling, har ytterligare en annan typ av telomerer. Dessa består av relativt långa, komplexa tandemrepeterade sekvenser, vilka hos C. pallidivittatus är belägna i 50-200 kilobaspar stora block. Varje repeterad sekvens är 340 baspar lång och de flesta tillhör en av fyra så kallade subfamiljer, vilka skiljer sig från varandra endast i små muterade segment. Huvudmålet i avhandlingen har varit att försöka förstå dessa olika subfamiljers möjliga funktioner. Ett första steg var en kartläggning av deras fördelning, både intra- och intertelomert. Intertelomert visade subfamiljerna en specifik fördelning där alla ej var representerade i varje telomer. I de telomerer som innehöll flera subfamiljer identifierades den mest distalt och mest proximalt belägna subfamiljen. Dessutom karaktäriserades den mest distala delen av subtelomert DNA i C. tentans och C. pallidivittatus samt gränsområdet mellan denna och de telomera repeterade enheterna. Studien av telomert DNA beläget intill gränsen mot subtelomera sekvenser gav oss möjlighet att dra slutsatser angående vilka mekanismer som är verksamma vid den informationsöverföring som sker mellan telomera repeterade enheter i olika kromosomändar. Indikationer har tidigare funnits att de telomera repeterade sekvenserna transkriberas. Denna fråga undersöktes både med avseende på möjliga funktionella roller för de olika subfamiljerna samt om transkriptionen skulle kunna ha ett samband med telomerernas förlängning. (Less)
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author
supervisor
opponent
  • Dr Olins, Donald E, The University of Tennessee-Oak Ridge Graduate School of Biomedical Sciences, USA
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Genetics, Chironomus, subtelomere, gene conversion, subfamilies, telomere, complex repeats, cytogenetics, Genetik, cytogenetik
pages
90 pages
publisher
Department of Genetics, Lund University
defense location
Blå hallen, Ekologihuset, Sölvegatan 37, Lund
defense date
1997-12-13 10:15:00
external identifiers
  • other:ISRN: LUNDBDS/NBGE 1029/001-090 (1997)
language
English
LU publication?
yes
additional info
The information about affiliations in this record was updated in December 2015. The record was previously connected to the following departments: Genetics (Closed 2011) (011005100)
id
d315e1b2-c16e-4e9a-9961-3a92fb4d76cf (old id 29719)
date added to LUP
2016-04-04 10:00:11
date last changed
2018-11-21 20:56:09
@phdthesis{d315e1b2-c16e-4e9a-9961-3a92fb4d76cf,
  abstract     = {{Telomeres in Chironomus consist of long complex tandem DNA repeats, which in C. pallidivittatus have been shown to extend to the extreme end of chromosomes. In C. pallidivittatus the telomeric repeats are present in large blocks, 50-200kb in size, most of them belonging to four major subfamilies. The main issue of this thesis has been to elucidate possible functional roles for these different subfamilies of telomeric repeats. Therefore, both intra- and intertelomeric mapping of the subfamilies were performed. One subfamily was found always to be located distally to the others, and have properties that could indicate a role in the protection of the chromosome ends. The subfamily identity of the most proximally situated repeat was identified in five of the seven non-telocentric chromosome ends. The junction between telomeric repeats and subterminal sequences was also characterized. In this region species and junction specific mutations were found, which were highly conserved between different chromosome ends within the same species. The homogenization pattern of these mutations indicated that gene conversion can act also between heterologous telomeres. The telomeric repeats exhibit a remarkable efficient homogenization whether they are located in the same or in different non-homologous chromosomes, an unusual feature since intrachromosomal homogenization usually are more efficient than homogenization between heterologues. Results from several earlier investigations had suggested transcriptional activity in the telomeric repeats in Chironomus. This issue was now addressed both in relation to possible roles for the different subfamilies in this transcription, and if this could be a connection to a process active in the elongation of the telomeres.}},
  author       = {{Kamnert, Iréne}},
  keywords     = {{Genetics; Chironomus; subtelomere; gene conversion; subfamilies; telomere; complex repeats; cytogenetics; Genetik; cytogenetik}},
  language     = {{eng}},
  publisher    = {{Department of Genetics, Lund University}},
  school       = {{Lund University}},
  title        = {{Classes of DNA associated with telomeres in the chironomids C. pallidivittatus and C. tentans}},
  year         = {{1997}},
}