RESUMEN
Escape from X inactivation results in expression of genes embedded within inactive chromatin, suggesting the existence of boundary elements between domains. We report that the 5' end of Jarid1c, a mouse escape gene adjacent to an inactivated gene, binds CTCF, displays high levels of histone H3 acetylation, and functions as a CTCF-dependent chromatin insulator. CpG island methylation at Jarid1c was very low during development and virtually absent at the CTCF sites, signifying that CTCF may influence DNA methylation and chromatin modifications. CTCF binding sites were also present at the 5' end of two other escape genes, mouse Eif2s3x and human EIF2S3, each adjacent to an inactivated gene, but not at genes embedded within large escape domains. Thus, CTCF was specifically bound to transition regions, suggesting a role in maintaining both X inactivation and escape domains. Furthermore, the evolution of X chromosome domains appears to be associated with repositioning of chromatin boundary elements.
Asunto(s)
Cromatina/metabolismo , Islas de CpG/fisiología , Proteínas de Unión al ADN/metabolismo , Compensación de Dosificación (Genética) , Regulación del Desarrollo de la Expresión Génica/fisiología , Proteínas Represoras/metabolismo , Acetilación , Animales , Sitios de Unión , Factor de Unión a CCCTC , Células Cultivadas , Metilación de ADN , Ensayo de Cambio de Movilidad Electroforética/métodos , Embrión de Mamíferos , Factor 2 Eucariótico de Iniciación/metabolismo , Histona Demetilasas , Humanos , Inmunoprecipitación/métodos , Ratones , Ratones Endogámicos C57BL , Modelos Moleculares , Datos de Secuencia Molecular , Mutagénesis/fisiología , Oxidorreductasas N-Desmetilantes , Proteínas/metabolismo , Cromosoma XRESUMEN
We have performed X-inactivation and sequence analyses on 350 kb of sequence from human Xp11.2, a region shown previously to contain a cluster of genes that escape X inactivation, and we compared this region with the region of conserved synteny in mouse. We identified several new transcripts from this region in human and in mouse, which defined the full extent of the domain escaping X inactivation in both species. In human, escape from X inactivation involves an uninterrupted 235-kb domain of multiple genes. Despite highly conserved gene content and order between the two species, Smcx is the only mouse gene from the conserved segment that escapes inactivation. As repetitive sequences are believed to facilitate spreading of X inactivation along the chromosome, we compared the repetitive sequence composition of this region between the two species. We found that long terminal repeats (LTRs) were decreased in the human domain of escape, but not in the majority of the conserved mouse region adjacent to Smcx in which genes were subject to X inactivation, suggesting that these repeats might be excluded from escape domains to prevent spreading of silencing. Our findings indicate that genomic context, as well as gene-specific regulatory elements, interact to determine expression of a gene from the inactive X-chromosome.
Asunto(s)
Cromosomas Humanos X/genética , Secuencia Conservada/genética , Compensación de Dosificación (Genética) , Actinas/genética , Animales , Células CHO , Línea Celular , Mapeo Cromosómico , Cricetinae , Etiquetas de Secuencia Expresada , Genes/genética , Humanos , Secuencias Repetitivas Esparcidas/genética , Elementos de Nucleótido Esparcido Largo/genética , Masculino , Ratones , Datos de Secuencia Molecular , Especificidad de Órganos/genética , Seudogenes/genética , Homología de Secuencia de Ácido Nucleico , Transcripción Genética , Cromosoma X/genéticaRESUMEN
Oral-facial-digital type 1 (OFD1) syndrome is an X-linked dominant condition characterized by malformations of the face, oral cavity, and digits. The responsible gene, OFD1, maps to human Xp22 and has an unknown function. We isolated and characterized the mouse Ofd1 gene and showed that it is subject to X-inactivation, in contrast to the human gene. Furthermore, we excluded a role for Ofd1 in the pathogenesis of the spontaneous mouse mutant Xpl, which had been proposed as a mouse model for this condition. Comparative sequence analysis demonstrated that OFD1 is conserved among vertebrates and absent in invertebrates. This analysis allowed the identification of evolutionarily conserved domains in the protein. Finally, we report the identification of 18 apparently nonfunctional OFD1 copies, organized in repeat units on the human Y chromosome. These degenerate OFD1-Y genes probably derived from the ancestral Y homologue of the X-linked gene. The high level of sequence identity among the different units suggests that duplication events have recently occurred during evolution.