Molecular characterization of the <i>Anopheles gambiae</i> 2L telomeric region via an integrated transgene

Biessmann, Harald; Donáth, Judit; Walter, Marika F.

doi:10.1111/j.1365-2583.1996.tb00035.x

Cited by 42 publications

(67 citation statements)

References 48 publications

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“…The simplest model to explain the observations that the 2L chromosome extensions are composed of sequences already present near the end of the chromosome and do not contain any new sequences typical of telomerase elongation or transpositions is that the chromosomes elongate by an unequal crossing over mechanism. The early mapping of the pUChsneo transgene in the G418 A. gambiae stock (11) together with recent detailed studies (3) indicated that a complete and a partial copy of the transgene were integrated at or near the end of the chromosome. We propose that this chance integration allowed elongation of the chromosome by terminal gene conversion as shown diagrammatically in Fig.…”

Section: Discussionmentioning

confidence: 99%

“…Due to size heterogeneity, the terminal DNA fragments from a pool of approximately 50 mosquitoes appeared as a broad band characteristic of chromosome termini (3). In order to assess the extent of size polymorphism at the telomere, DNA from individual mosquitoes was assayed.…”

Section: L Chromosome Ends In 1993mentioning

confidence: 99%

“…The plasmid conferring resistance to the neomycin analog G418 to the transformed mosquitoes integrated fortuitously into the extreme end of chromosome 2L (11). We have recently reported on the cloning and characterization of the A. gambiae flanking DNA at the proximal end of the integration, which consists of a tandem array of 0.8-kb repeats (3). In the present study, we cloned and sequenced the 2L chromosome end and examined the dynamics of chromosome length variation.…”

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confidence: 99%

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Chromosome End Elongation by Recombination in the MosquitoAnopheles gambiae

Roth

Kobeski

Walter

et al. 1997

Molecular and Cellular Biology

108

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One of the functions of telomeres is to counteract the terminal nucleotide loss associated with DNA replication. While the vast majority of eukaryotic organisms maintain their chromosome ends via telomerase, an enzyme system that generates short, tandem repeats on the ends of chromosomes, other mechanisms such as the transposition of retrotransposons or recombination can also be used in some species. Chromosome end regression and extension were studied in a medically important mosquito, the malaria vector Anopheles gambiae, to determine how this dipteran insect maintains its chromosome ends. The insertion of a transgenic pUChsneo plasmid at the left end of chromosome 2 provided a unique marker for measuring the dynamics of the 2L telomere over a period of about 3 years. The terminal length was relatively uniform in the 1993 population with the chromosomes ending within the white gene sequence of the inserted transgene. Cloned terminal chromosome fragments did not end in short repeat sequences that could have been synthesized by telomerase. By late 1995, the chromosome ends had become heterogeneous: some had further shortened while other chromosomes had been elongated by regenerating part of the integrated pUChsneo plasmid. A model is presented for extension of the 2L chromosome by recombination between homologous 2L chromosome ends by using the partial plasmid duplication generated during its original integration. It is postulated that this mechanism is also important in wild-type telomere elongation.Telomeres are essential chromosomal structures whose functional integrity is linked to cell cycle progression. Considerable efforts are being made to understand telomere structure and to target elongation mechanisms in order to develop new means of proliferation control (12). Every eukaryotic organism must compensate for terminal loss of DNA from chromosome ends because DNA polymerases cannot completely replicate the ends of linear chromosomes. So far, evidence for three different terminal elongation mechanisms has been established. Most eukaryotes have a short, tandemly repeated DNA sequence motif on their chromosome ends. These telomeric tandem arrays are extended by a specific reverse transcriptase, telomerase, which carries an internal RNA template (12). Alternatively, Drosophila melanogaster elongates its telomeres by a very different mechanism that is based on transpositions of specific retrotransposons, HeT-A and TART, to chromosome termini (22). In addition, recombination of repetitive telomeric ends has been considered as a possible elongation mechanism (4, 10, 42). This pathway has been well documented in yeast where telomeres are extended by telomerase, but recombination can be used as an efficient bypass mechanism for elongation (19,20,30,39).Understanding the mechanism of telomere elongation in the malaria-transmitting mosquito Anopheles gambiae may be useful for developing new strategies for vector control. Therefore, we examined the dynamics of chromosome length variation at the 2L chromosome end. For...

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Section: Discussionmentioning

confidence: 99%

Section: L Chromosome Ends In 1993mentioning

confidence: 99%

mentioning

confidence: 99%

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Chromosome End Elongation by Recombination in the MosquitoAnopheles gambiae

Roth

Kobeski

Walter

et al. 1997

Molecular and Cellular Biology

108

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“…Recombination between these complex repeat sequences has been proposed as a mechanism for chromosome length maintenance in these species. It should be noted that 'lower' dipterans, such as the midge Chironomus and the mosquito Anopheles, which may resemble a Drosophila ancestor, fall into this category (55,98,99).…”

Section: Evolution Of Drosophila Telomeresmentioning

confidence: 99%

Drosophila telomeres: an exception providing new insights

2007

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SummaryDrosophila telomeres are comprised of DNA sequences that differ dramatically from those of other eukaryotes. Telomere functions, however, are similar to those found in telomerase-based telomeres, even though the underlying mechanisms may differ. Drosophila telomeres use arrays of retrotransposons to maintain chromosome length, while nearly all other eukaryotes rely on telomerase-generated short repeats. Regardless of the DNA sequence, several end-binding proteins are evolutionarily conserved. Away from the end, the Drosophila telomeric and subtelomeric DNA sequences are complexed with unique combinations of proteins that also modulate chromatin structure elsewhere in the genome. Maintaining and regulating the transcriptional activity of the telomeric retrotransposons in Drosophila requires specific chromatin structures, and while telomeric silencing spreads from the terminal repeats in yeast, the source of telomeric silencing in Drosophila is the subterminal arrays. However, the subterminal arrays in both species may be involved in telomere-telomere associations and/or communication.

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“…The ends of chromosomes in the fruit fly Drosophila melanogaster are maintained by occasional transposition of retrotransposons (4,24,53). Other organisms, including the midge Chironomus sp., the mosquito Anopheles gambiae, and the plant Alium cepa, have telomeres composed of complex repeat families that are thought to be maintained by recombination (5,13,43,47).…”

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confidence: 99%

Recombinational Telomere Elongation Promoted by DNA Circles

Natarajan

McEachern

2002

Molecular and Cellular Biology

112

132

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Yeast mutants lacking telomerase are capable of maintaining telomeres by an alternate mechanism that depends on homologous recombination. We show here, by using Kluyveromyces lactis cells containing two types of telomeric repeats, that recombinational telomere elongation generates a repeating pattern common in most or all telomeres in survivors that retain both repeat types. We propose that these patterns arise from small circles of telomeric DNA being used as templates for rolling-circle gene conversion and that the sequence from the lengthened telomere is spread to other telomeres by additional, more typical gene conversion events. Consistent with this, artificially constructed circles of DNA containing telomeric repeats form long tandem arrays at telomeres when transformed into K. lactis cells. Mixing experiments done with two species of telomeric circles indicated that all of the integrated copies of the transforming sequence arise from a single original circular molecule.

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Molecular characterization of the Anopheles gambiae 2L telomeric region via an integrated transgene

Cited by 42 publications

References 48 publications

Chromosome End Elongation by Recombination in the MosquitoAnopheles gambiae

Chromosome End Elongation by Recombination in the MosquitoAnopheles gambiae

Drosophila telomeres: an exception providing new insights

Recombinational Telomere Elongation Promoted by DNA Circles

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