Telomeric DNA in Chironomus, a naturally telomerase-free system

Research output: ThesisDoctoral Thesis (compilation)

Standard

Telomeric DNA in Chironomus, a naturally telomerase-free system. / Rosén, Monika.

Department of Genetics, Lund University, 2001. 130 p.

Research output: ThesisDoctoral Thesis (compilation)

Harvard

Rosén, M 2001, 'Telomeric DNA in Chironomus, a naturally telomerase-free system', Doctor, Department of Biology.

APA

Rosén, M. (2001). Telomeric DNA in Chironomus, a naturally telomerase-free system. Department of Genetics, Lund University.

CBE

Rosén M. 2001. Telomeric DNA in Chironomus, a naturally telomerase-free system. Department of Genetics, Lund University. 130 p.

MLA

Rosén, Monika Telomeric DNA in Chironomus, a naturally telomerase-free system Department of Genetics, Lund University. 2001.

Vancouver

Rosén M. Telomeric DNA in Chironomus, a naturally telomerase-free system. Department of Genetics, Lund University, 2001. 130 p.

Author

Rosén, Monika. / Telomeric DNA in Chironomus, a naturally telomerase-free system. Department of Genetics, Lund University, 2001. 130 p.

RIS

TY - THES

T1 - Telomeric DNA in Chironomus, a naturally telomerase-free system

AU - Rosén, Monika

N1 - Defence details Date: 2001-12-14 Time: 10:15 Place: Department of Genetics, Sölvegatan 29, Lund External reviewer(s) Name: Grossbach, Ulrich Title: Prof Affiliation: Göttingen, Germany --- 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), Invertebral Developmental Biology, Udo Haecker's group (013212048)

PY - 2001

Y1 - 2001

N2 - Telomeres are specialized complexes of DNA and associated proteins that protect the ends of eukaryotic chromosomes. Although most organisms have short repeated DNA sequences at their telomeres, which are specified and maintained by the enzyme telomerase, there are a few exceptions. Dipteran insects, including the genus Chironomus (non-biting midges), lack telomerase and have atypical terminal sequences. Chironomids have four chromosomes – three metacentric and one telocentric. In C. pallidivittatus, long (340 bp) and complex telomere-specific repeats terminate the seven nontelocentric chromosome ends and a similar situation probably occurs in related species. Although this DNA evolves rapidly, it is shown here that some sequence features are conserved among three analyzed Chironomus species, including C. pallidivittatus. Another one of these species (C. tentans) was found to lack the long single-stranded overhangs characteristic of canonical telomeres (those maintained by telomerase). The eighth, telocentric chromosome end, on the other hand, contains 155 bp centromere-specific repeats. In this study, it is shown that these 155 bp units extend to the very end of the chromosome. Consequently, it appears that one and the same cell can use different terminating repeats at different chromosome ends. The telocentric end is also unique in that it was found to contain an active gene, probably derived from a transposon, close to the telocentric repeat array. This gene could be involved in maintenance of the adjoining telomere and requires further investigation. Previous studies have shown that gene conversion is one factor in the maintenance of telomeric DNA at nontelocentric chromosome ends. The possibility of RNA-based telomere elongation, which was suggested by earlier immunolocalization of reverse transcriptase to telomeres, was addressed here. A previously identified RNase-sensitive fraction, hybridizing to telomeric repeats was found to be a double-stranded extrachromosomal component containing both DNA and RNA and to be unique to telomeres. However, additional research is required in order to evaluate the possible role of this material in telomere maintenance.

AB - Telomeres are specialized complexes of DNA and associated proteins that protect the ends of eukaryotic chromosomes. Although most organisms have short repeated DNA sequences at their telomeres, which are specified and maintained by the enzyme telomerase, there are a few exceptions. Dipteran insects, including the genus Chironomus (non-biting midges), lack telomerase and have atypical terminal sequences. Chironomids have four chromosomes – three metacentric and one telocentric. In C. pallidivittatus, long (340 bp) and complex telomere-specific repeats terminate the seven nontelocentric chromosome ends and a similar situation probably occurs in related species. Although this DNA evolves rapidly, it is shown here that some sequence features are conserved among three analyzed Chironomus species, including C. pallidivittatus. Another one of these species (C. tentans) was found to lack the long single-stranded overhangs characteristic of canonical telomeres (those maintained by telomerase). The eighth, telocentric chromosome end, on the other hand, contains 155 bp centromere-specific repeats. In this study, it is shown that these 155 bp units extend to the very end of the chromosome. Consequently, it appears that one and the same cell can use different terminating repeats at different chromosome ends. The telocentric end is also unique in that it was found to contain an active gene, probably derived from a transposon, close to the telocentric repeat array. This gene could be involved in maintenance of the adjoining telomere and requires further investigation. Previous studies have shown that gene conversion is one factor in the maintenance of telomeric DNA at nontelocentric chromosome ends. The possibility of RNA-based telomere elongation, which was suggested by earlier immunolocalization of reverse transcriptase to telomeres, was addressed here. A previously identified RNase-sensitive fraction, hybridizing to telomeric repeats was found to be a double-stranded extrachromosomal component containing both DNA and RNA and to be unique to telomeres. However, additional research is required in order to evaluate the possible role of this material in telomere maintenance.

KW - Biology

KW - Chironomus

KW - extrachromosomal telomeric repeats

KW - RNA-DNA complex

KW - 3´overhang

KW - telocentric chromosome end

KW - Telomere

KW - complex repeats

KW - Biologi

KW - Genetics

KW - cytogenetics

KW - Genetik

KW - cytogenetik

M3 - Doctoral Thesis (compilation)

SN - 91-7874-168-8

PB - Department of Genetics, Lund University

ER -