Characterization of DNA sequences constituting the terminal heterochromatin of the chicken Z chromosome

• Published in: Chromosome research Vol. 4; no. 6; p. 411
• Main Authors: Hori, T, Suzuki, Y, Solovei, I, Saitoh, Y, Hutchison, N, Ikeda, J E, Macgregor, H, Mizuno, S
• Format: Journal Article
• Language: English
• Published: Netherlands 01.09.1996
• Subjects: Animals; Base Sequence; Chickens; DNA - chemistry; Electrophoresis, Gel, Two-Dimensional; Female; Genomic Library; Heterochromatin - chemistry; In Situ Hybridization, Fluorescence; Microsatellite Repeats; Molecular Sequence Data; Repetitive Sequences, Nucleic Acid; Restriction Mapping
• ISSN: 0967-3849; 1573-6849
• DOI: 10.1007/bf02265048

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. Fluorescence in 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 pCZTH-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 sequences 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 pCZTH-8 sequence has no internal repeats and may be part of the 24-kb macrosatellite repeating unit that is evident after Nhel 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 methylated in 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 pCZTH-8 are restricted to the genus Gallus but the sequence of one subregion which hybridizes to TBLs is present in the genomes of the order Galliformes.