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Title: The position of repetitive DNA sequence in the southern cattle tick genome permits chromosome identification

item Guerrero, Felicito

Submitted to: Chromosome Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2008
Publication Date: 2/17/2009
Citation: Hill, C.A., Guerrero, F.D., Van Zee, J.P., Geraci, N.S., Walling, J.G., Stuart, J.J. 2009. The position of repetitive DNA sequence in the southern cattle tick genome permits chromosome identification. Chromosome Research. 17:77-89.

Interpretive Summary: The structure of chromosomes from the southern cattle tick, Rhipicephalus microplus, was studied by the technique of Fluorescent in situ hybridization (FISH). Little is known about the chromosomes of this tick and chromosome mapping techniques which enable the localization of specific genes to specific chromosomes will be very important to the assembly of the tick's genome sequence. We found specific probes which can be used to unambiguously identify each of the autosomes and the X chromosome of the tick. We also adapted labelling and hybridization techniques to allow cDNAs and large DNA clones known as BACs to be localized on the tick chromosomes. Specific DNA repetitive sequences were found which will provide useful markers to investigate tick chromosome biology and advance studies of tick population genetics.

Technical Abstract: Fluorescent in situ hybridization (FISH) using meiotic chromosome preparations and highly repetitive DNA from the southern cattle tick, Rhipicephalus microplus, was undertaken to investigate genome organization. Several classes of highly repetitive DNA elements were identified by screening a R. microplus Bacterial Artificial Chromosome (BAC) library. A repeat unit of approximately 149 bp, RMR-1 was localized to the subtelomeric regions of R. microplus autosomes 1-6 and 8-10. A second repeat unit, RMR-2 was localized to the sub-telomeric regions of all autosomes and the X chromosome. RMR-2 was composed of three distinct repeat populations, RMR-2a, RMR-2b and RMR-2c of 178, 177 and 216 bp in length, respectively. Localization of an rDNA probe identified a single nucleolar organizing region on one autosome. Using a combination of labeled probes, we developed a preliminary karyotype for R. microplus. We present evidence that R. microplus has holocentric chromosomes and explore the implications of these findings for tick chromosome biology and genomic research.