Characterization of DNA sequences constituting the terminal heterochromatin of the chicken Z chromosome |
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| Authors: | Tetsuya Hori Yukiko Suzuki Irina Solovei Yasushi Saitoh Nancy Hutchison Joh-E Ikeda Herbert Macgregor Shigeki Mizuno |
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| Institution: | (1) Laboratory of Molecular Biology, Department of Applied Biological Chemistry, Faculty of Agriculture, Tohoku University, Aoba-ku, 981 Sendai, Japan;(2) Biological Institute, University of St Petersburg, St Petersburg, Russia;(3) Institute of Medical Science, Tokai University School of Medicine, Isehara, Kanagawa, Japan;(4) Fred Hutchinson Cancer Research Center, Seattle, WA, USA;(5) Department of Zoology, University of Leicester, Leicester, UK |
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| Abstract: | Two clones, pCZTH5-8 and pCZTH12-8, were isolated from a female chicken genomic library by screening with sequences obtained from genomic libraries which had been constructed from a terminal region of a single Z chromosome of chicken utilizing laser microbeam irradiation and PCR amplification. Fluorescencein situ hybridization to the mitotic Z chromosome and the lampbrush ZW bivalent of chicken demonstrated that both the cloned sequences are located in the heterochromatic region of the Z chromosome at the end opposite to the pairing region with the W chromosome. The sequences pCZTH5-8 and pCZTH12-8 are distributed widely on both the telomeric bow-like loops (TBL) and the region I (short loops region) of the Z lampbrush chromosome. These clones, pCZTH12-8 particularly notably, hybridized also to the TBLs of lampbrush bivalents 1–4 of chicken. Both sequence are transcribed in the lampbrush stage oocytes on the Z chromosome and on other macrobivalents. The subfragment of pCZTH5-8 which hybridizes to the TBLs and the insert of pCZTH12-8 contain regions that are closely similar in sequence. The pCZTH5-8 sequence has no internal repeats and may be part of the 24-kb macrosatellite repeating unit that is evident afterNhel digestion of the genomic DNA. A cloned 24-kb unit, pFN-1, does not show significant DNA curvature, but cytosines of its CpG dinucleotides may be highly methylatedin vivo. This contrasts with the repeat sequences of the W heterochromatin which not only have highly methylated CpG but are also strongly curved. The 24-kb unit is repeated about 830 times in the diploid genome of a female chicken, suggesting that nearly the entire terminal heterochromatin on the Z chromosome consists of this macrosatellite family. Sequences of the greater part of the pCZTH5-8 are restricted to the genusGallus but the sequence of one subregion which hybridizes to TBLs is present in the genomes of the order Galliformes.accepted for publication by M. Schmid |
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| Keywords: | fluorescencein situ hybridization Gallus heterochromatin macrosatellite DNA Z chromosome |
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