X chromosome inactivation is the chromosome-based silencing mechanism eutherian mammals use to equalize the expression of X-linked genes between males and females early in development. To achieve transcriptional silencing of genes on 1 X chromosome each cell of a female must determine the number of X chromosomes it contains, choose 1 X to inactivate and initiate, propagate and maintain chromosome wide silencing. An elusive component of the X inactivation pathway is the initial choice between the 2 X chromosomes. In the mouse, choice is under the control of the X-controlling element (Xce), a genetically defined locus within the X inactivation center. Xce heterozygotes exhibit skewed, nonrandom inactivation of the X chromosome in somatic tissues. The objective of this proposal is to study X chromosome choice in mice. We previously conducted a phenotype-driven genetic screen involving chemical mutagenesis in the mouse and identified 3 genetically distinct autosomal mutations with dominant effects on X chromosome choice early in embryogenesis. This proposal will investigate the mechanism of X chromosome choice by: (1) Refining the map locations and cloning the genes responsible for the X chromosome choice mutations obtained in the genetic screen; (2) Isolating and characterizing embryonic stem cell lines from each of the mutant strains so that the earliest steps in the X inactivation process can be molecularly and biochemically monitored and manipulated; (3) Fine mapping and further characterizing the Xce. Elucidating the cis-acting sequences and the trans-acting factors involved in X chromosome choice will allow a greater understanding of the complex process of X inactivation. Furthermore, a better understanding of X chromosome choice will improve our knowledge of how differences in allelic ratios can result in significant phenotypic variation, including how unfavorable X chromosome skewing can lead to more severe phenotypes in a variety of X linked diseases.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM074768-04
Application #
7477964
Study Section
Genetics of Health and Disease Study Section (GHD)
Program Officer
Carter, Anthony D
Project Start
2005-08-01
Project End
2010-07-31
Budget Start
2008-08-01
Budget End
2010-07-31
Support Year
4
Fiscal Year
2008
Total Cost
$291,211
Indirect Cost
Name
University of Pennsylvania
Department
Anatomy/Cell Biology
Type
Schools of Medicine
DUNS #
042250712
City
Philadelphia
State
PA
Country
United States
Zip Code
19104
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Weaver, Jamie R; Susiarjo, Martha; Bartolomei, Marisa S (2009) Imprinting and epigenetic changes in the early embryo. Mamm Genome 20:532-43
Ideraabdullah, Folami Y; Vigneau, Sebastien; Bartolomei, Marisa S (2008) Genomic imprinting mechanisms in mammals. Mutat Res 647:77-85
Thorvaldsen, Joanne L; Verona, Raluca I; Bartolomei, Marisa S (2006) X-tra! X-tra! News from the mouse X chromosome. Dev Biol 298:344-53
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