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Tandemly Repeated and Satellite DNA in the Drosophila and the D. buzzatii cluster

Long-range organisation of two non-homologous satellite DNAs from the Drosophila buzzatii cluster: Mutual relative arrangements and molecular drive

Gustavo C.S. Kuhn, 1 ; Schwarzacher, Trude 2 ; S. Heslop-Harrison, John 2
1 Federal University of Sao Carlos, Department of Genetics and Evolution, Sao Carlos - SP, BRAZIL;
2 University of Leicester, Department of Biology, Leicester, UNITED KINGDOM

Repetitive DNA sequences are among the most dynamic genomic components, and their evolution is important for genome behaviour and speciation. The evolution of satellite DNAs is influenced by several mechanisms of non-reciprocal exchanges that promote significant changes related to the copy-number of repeat variants within and between arrays. As a result, different variants might be homogenised and fixed in the genomes of different species, a process known as molecular drive. Two non-homologous satDNAs have been previously found in seven cactus-breeding Drosophila species: the pBuM family with alpha (180bp) and alpha/beta (370bp) repeats and the DBC-150 family with 150bp repeats. FISH on metaphase chromosomes revealed co-localization of alpha and alpha/beta in several chromosomes and pBuM and DBC-150 in the microchromosomes. High-resolution analysis of the satDNAs using FISH on extended DNA fibres revealed several complex patterns of pBuM-array organisation, from pure alpha arrays to pure alpha/beta arrays, with several intermediate types. The distribution of these array-types varies significantly from one species to another, providing an interesting opportunity to analyse transitional stages of turnover of satDNA variants during the evolution of a group of closely related species. Apart from pure pBuM and DBC-150 arrays, monomers of both families have also been found arranged in a highly interspersed pattern. There are only few examples demonstrating this type of satDNA organisation in other organisms. Altogether, high resolution physical mapping gives insights into topics related to the origin, homogenisation and turnover of satDNA repeats and arrays (www.drosophila.molcyt.com). Kuhn was supported by CAPES (1158/06-6).

We have projects on tandemly repeated DNA evolution in animal and plant species.

In animals, these projects involve the Drosophila buzzatii cluster (with Gustavo Kuhn), Bovids (Raquel Chaves) and scallops (Assunta Biscotti and Ettore Olmo, publication 248).

Satellite DNAs (satDNAs) are ubiquitous components of the eukaryotic genome, consisting of tandemly repetitive DNA sequences organized in long monotonic arrays of hundreds or thousands of copies usually located in the heterochromatic regions of chromosomes, mainly near the centromere, but sometimes in sub-telomeric regions. Several satDNA families with independent origin are usually found in the genome of the same species or group of species (Ugarkovic and Plohl 2002).

Our research group is very interested in tandemly repeated DNA evolution in Drosophila. We have been working with these sequences in the seven species of the Drosophila buzzatii cluster (Gustavo Kuhn), and are initiating projects to analyse the repetitive, tandemly repeated satellite DNA in the genomes of the 12 sequenced Drosophila genomes (Noncoding DNA of the Assembly, Alignment and Annotation of 12 Drosophila genomes project).

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