Early in embryonic development, one of the two X chromosomes in mammalian females becomes heterochromatic, late replicating, and largely genetically inactive as a means of dosage compensation for X-linked genes. Once established, this inactivation is irreversible and clonally stable in somatic cells. While the basic features of X inactivation have been well established for some time, the molecular basis for the initiation and promulgation of this chromosome-based cis-regulatory signal remains unknown. The proposed research will address a number of key questions regarding fundamental aspects of the X inactivation process. How does the process initiate early in embryogenesis? Are one or more X inactivation centers required for initiation? If a specific locus is required for initiation of X inactivation, is it also required for the maintenance of inactivation through successive cell divisions? What proportion of genes are subject to inactivation and what proportion """"""""escape"""""""" inactivation? Are inactivated and non-inactivated genes clustered in specific regions of the chromosome or is X inactivation controlled on a locus basis? How is it determined which genes respond to and which genes are refractory to the X inactivation signal? Our analysis of human X chromosome inactivation will focus initially on the genetic basis for the initiation and maintenance of X inactivation and on the nature of genes that escape inactivation.
The specific aims of the proposed research are: (i) to examine the transcriptional basis for inactivation of X-linked genes in a series of human/mouse somatic cell hybrids retaining either """"""""active"""""""" X or """"""""inactive"""""""" X chromosomes; (ii) to identify and characterize new genes that escape the inactivation process by isolating human cDNA clones expressed from """"""""inactive"""""""" human X chromosomes; (iii) to test the hypothesis that there is a single region on the X responsible for X inactivation by examining structurally abnormal inactive X chromosomes in somatic cell hybrids to define the putative X inactivation center; (iv) to evaluate whether the continued presence of such a locus is required for the stable maintenance of the inactive X; (v) to isolate the X inactivation center in yeast artificial chromosomes; and (vi) to establish a system to examine human X chromosome and/or yeast artificial chromosomes carrying large fragments of DNA including candidate sequences for the human X inactivation center.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM045441-04
Application #
3304920
Study Section
Mammalian Genetics Study Section (MGN)
Project Start
1991-01-01
Project End
1995-01-31
Budget Start
1993-02-01
Budget End
1994-01-31
Support Year
4
Fiscal Year
1993
Total Cost
Indirect Cost
Name
Case Western Reserve University
Department
Type
Schools of Medicine
DUNS #
077758407
City
Cleveland
State
OH
Country
United States
Zip Code
44106
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Chadwick, Lisa Helbling; Pertz, Lisa M; Broman, Karl W et al. (2006) Genetic control of X chromosome inactivation in mice: definition of the Xce candidate interval. Genetics 173:2103-10
Amos-Landgraf, James M; Cottle, Amy; Plenge, Robert M et al. (2006) X chromosome-inactivation patterns of 1,005 phenotypically unaffected females. Am J Hum Genet 79:493-9
Chadwick, Lisa Helbling; Willard, Huntington F (2005) Genetic and parent-of-origin influences on X chromosome choice in Xce heterozygous mice. Mamm Genome 16:691-9
Chadwick, Brian P; Willard, Huntington F (2004) Multiple spatially distinct types of facultative heterochromatin on the human inactive X chromosome. Proc Natl Acad Sci U S A 101:17450-5
Chadwick, Brian P; Willard, Huntington F (2003) Barring gene expression after XIST: maintaining facultative heterochromatin on the inactive X. Semin Cell Dev Biol 14:359-67
Percec, Ivona; Thorvaldsen, Joanne L; Plenge, Robert M et al. (2003) An N-ethyl-N-nitrosourea mutagenesis screen for epigenetic mutations in the mouse. Genetics 164:1481-94
Chadwick, Brian P; Willard, Huntington F (2003) Chromatin of the Barr body: histone and non-histone proteins associated with or excluded from the inactive X chromosome. Hum Mol Genet 12:2167-78
Plenge, Robert M; Stevenson, Roger A; Lubs, Herbert A et al. (2002) Skewed X-chromosome inactivation is a common feature of X-linked mental retardation disorders. Am J Hum Genet 71:168-73

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