Centromeric inactivation in a dicentric human Y;21 translocation chromosome |
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Authors: | Andrew M Fisher Lihadh Al-Gazali T Pramathan Roger Quaife Annette E Cockwell John C K Barber William C Earnshaw Joyce Axelman Barbara R Migeon Chris Tyler-Smith |
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Institution: | (1) Wessex Regional Genetics Laboratory, Salisbury District Hospital, Salisbury, Wiltshire, SP2 8BJ, UK, GB;(2) Department of Paediatrics, Faculty of Medicine & Health Sciences, UAE University, Al Ain, United Arab Emirates, AE;(3) The Riyadh Armed Forces Hospital, Department of Pathology, Division of Genetics, P.O. Box 7897, Riyadh 11159, Kingdom of Saudi Arabia, SA;(4) Department of Cell Biology and Anatomy, Johns Hopkins School of Medicine, Baltimore, MD 21205, USA, TP;(5) Center for Medical Genetics, Johns Hopkins University School of Medicine, 600 North Wolfe Street, CMSC 1004, Baltimore, MD 21287-3914, USA, TP;(6) CRC Chromosome Molecular Biology Group, Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK, GB |
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Abstract: | A de novo dicentric Y;21 (q11.23;p11) translocation chromosome with one of its two centromeres inactive has provided the opportunity
to study the relationship between centromeric inactivation, the organization of alphoid satellite DNA and the distribution
of CENP-C. The proband, a male with minor features of Down’s syndrome, had a major cell line with 45 chromosomes including
a single copy of the translocation chromosome, and a minor one with 46 chromosomes including two copies of the translocation
chromosome and hence effectively trisomic for the long arm of chromosome 21. Centromeric activity as defined by the primary
constriction was variable: in most cells with a single copy of the Y;21 chromosome, the Y centromere was inactive. In the
cells with two copies, one copy had an active Y centromere (chromosome 21 centromere inactive) and the other had an inactive
Y centromere (chromosome 21 centromere active). Three different partial deletions of the Y alphoid array were found in skin
fibroblasts and one of these was also present in blood. Clones of single cell origin from fibroblast cultures were analysed
both for their primary constriction and to characterise their alphoid array. The results indicate that (1) each clone showed
a fixed pattern of centromeric activity; (2) the alphoid array size was stable within a clone; and (3) inactivation of the
Y centromere was associated with both full-sized and deleted alphoid arrays. Selected clones were analysed with antibodies
to CENP-C, and staining was undetectable at both intact and deleted arrays of the inactive Y centromeres. Thus centromeric
inactivation appears to be largely an epigenetic event.
Received: 30 January 1997; in revised form: 3 April 1997 / Accepted: 8 May 1997 |
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