Characterization of DNA sequences constituting the terminal heterochromatin of the chicken Z chromosome.
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.
Department of APplied Biological Chemistry, Faculty of Agriculture, Tohoku University, Sendai, Japan.
T
T
Hori
Y
Y
Suzuki
I
I
Solovei
Y
Y
Saitoh
N
N
Hutchison
J E
JE
Ikeda
H
H
Macgregor
S
S
Mizuno
D000818:Animals; D001483:Base Sequence; D002645:Chickens; D004247:DNA / Q000737:chemistry*; D015180:Electrophoresis, Gel, Two-Dimensional; D005260:Female; D015698:Genomic Library; D006570:Heterochromatin / Q000737:chemistry*; D017404:In Situ Hybridization, Fluorescence; D018895:Microsatellite Repeats; D008969:Molecular Sequence Data; D012091:Repetitive Sequences, Nucleic Acid; D015183:Restriction Mapping
D006570:Heterochromatin; D004247:DNA