Tuyển tập các báo cáo nghiên cứu về y học được đăng trên tạp chí y học Wertheim cung cấp cho các bạn kiến thức về ngành y đề tài: Activity map of the tammar X chromosome shows that marsupial X inactivation is incomplete and escape is stochastic. | Al Nadaf et al. Genome Biology 2010 11 R122 http 2010 11 12 R122 Genome Biology RESEARCH Open Access Activity map of the tammar X chromosome shows that marsupial X inactivation is incomplete and escape is stochastic 1 12 123 12 1 12 Shafagh Al Nadaf Paul D Waters Edda Koina Janine E Deakin Kristen S Jordan Jennifer AM Graves Abstract Background X chromosome inactivation is a spectacular example of epigenetic silencing. In order to deduce how this complex system evolved we examined X inactivation in a model marsupial the tammar wallaby Macropus eugenii . In marsupials X inactivation is known to be paternal incomplete and tissue-specific and occurs in the absence of an XIST orthologue. Results We examined expression of X-borne genes using quantitative PCR revealing a range of dosage compensation for different loci. To assess the frequency of 1X- or 2X-active fibroblasts we investigated expression of 32 X-borne genes at the cellular level using RNA-FISH. In female fibroblasts two-color RNA-FISH showed that genes were coordinately expressed from the same X active X in nuclei in which both loci were inactivated. However loci on the other X escape inactivation independently with each locus showing a characteristic frequency of 1X-active and 2X-active nuclei equivalent to stochastic escape. We constructed an activity map of the tammar wallaby inactive X chromosome which identified no relationship between gene location and extent of inactivation nor any correlation with the presence or absence of a Y-borne paralog. Conclusions In the tammar wallaby one X presumed to be maternal is expressed in all cells but genes on the other paternal X escape inactivation independently and at characteristic frequencies. The paternal and incomplete X chromosome inactivation in marsupials with stochastic escape appears to be quite distinct from the X chromosome inactivation process in eutherians. We find no evidence for a polar spread of inactivation from an X inactivation
