Allele-specific binding of YY1 to the Xist and Tsix clusters. A) The in vivo YY1 binding to each cluster was tested with three primer sets, and the positions of these are indicated with arrows with numbers. (B) Female-specific binding of YY1 to the Xist cluster. Two mouse brain tissues from female (F1) and male (F2) were used for our ChIP experiments. Our ChIP analyses included two control DNAs: 10% of the Input DNAs from F1 (lane 1) and F2 (lane 4) and the immunoprecipitated DNA with preimmune serum (lanes 2 and 5). Our ChIP analyses used the Peg3 locus as an internal control for female- and male-derived ChIP DNAs as shown in the bottom. Asterisks indicate the regions enriched by YY1-Ab. (C) Schematic representation of allele-specific YY1 binding to the Xist locus based on the results of B. YY1 binds to the Xist cluster located in the Xi of female, which is unmethylated. Because of the repeat structure of the Tsix cluster, however, our ChIP analyses could not confirm the in vivo YY1 binding to this locus. The methylation status of Tsix reflects the gametic difference between two sexes before the onset of random XCI (X chromosome inactivation). For the imprinted XCI in female, Xa is from oocytes (maternal) while Xi is from sperm (paternal).
