Some genes on the inactive X chromosome escape silencing. One possible escape mechanism is that heterochromatization during X inactivation can be blocked by boundary elements. DNA insulators are candidates for blocking because they shield genes from influences of their chromosomal environment. To test whether DNA insulators can act as boundaries on the X chromosome, we inserted into the mouse X-linked Hprt locus a GFP transgene flanked with zero, one, or two copies of a prototypic vertebrate insulator from the chicken beta-globin locus, chicken hypersensitive site 4, which contains CCCTC binding factor binding sites. On the active X chromosome the insulators blocked repression of the transgene, which commences during early development and persists in adults, in a copy number-dependent manner. CpG methylation of the transgene correlated inversely with expression, but the insulators on the active X chromosome were not methylated. On the inactive X chromosome, insulators did not block random or imprinted X inactivation of the transgene, and both the insulator and transgene were almost completely methylated. Thus, the chicken hypersensitive site 4 DNA insulator is sufficient to protect an X-linked gene from repression during development but not from X inactivation.
We have not found any resources mentioned in this publication.
SciCrunch® is a data sharing and display platform. Anyone can create a custom portal where they can select searchable subsets of hundreds of data sources, brand their web pages and create their community. SciCrunch® will push data updates automatically to all portals on a weekly basis. User communities can also add their own data to SciCrunch®, however this is not currently a free service.