Genome organization of major tandem repeats in the

Authors: Jason M Meyer Timothy J Kurtti Janice P Van Zee Catherine A Hill

Publish Date: 2010/03/20

Volume: 18, Issue: 3, Pages: 357-370

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Abstract

In spite of the global medical and veterinary importance of Ixodid ticks relatively little is known about their genome organization To address this we developed the first fluorescence in situ hybridization FISHbased chromosome markers in the Lyme disease vector Ixodes scapularis Shotgun genomic DNA gDNA sequences were used to identify three major tandem repeat families which were localized to specific heterochromatic regions of I scapularis chromosomes prepared from the mitotic cell line ISE18 Together these repeats were estimated to contribute ∼159 Mb 8 of the 21 Gb haploid I scapularis genome The relative arrangement of each tandem repeat family and the nucleolar organizing regions was determined by rehybridization to individual chromosome spreads which was useful to distinguish different chromosomes in the ISE18 karyotype Long stretches 20 kb of tandem repeatcontaining gDNA were resistant to digestion by the methylationsensitive restriction enzyme HpaII and localized to the presumed pericentromeric regions of the chromosomes A telomeric probe based on the arthropodconserved TTAGG n tandemly repetitive motif was localized to the termini of each I scapularis chromosome Localization of these markers produced the first link between DNA sequences and major structural features of I scapularis chromosomes and thereby provided the framework for a FISHbased physical map

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