X-chromosome inactivation in hybrid embryonic carcinoma cells upon differentiation

We have analyzed Xist expression before and after the differentiation of embryonic carcinoma (EC) cell hybrids to address whether these hybrids undergo X inactivation on differentiation in vitro and whether this process (X inactivation) is random. In this work, we analyzed Xist expression using RT-PCR as a way of monitoring the X-chromosome activity in EC hybrid cells. No Xist expression was observed in OTF9 or in its hybrid cells, indicating that all X chromosomes were active in these cells. In contrast, retinoic acid-induced differentiated cells expressed as high levels of Xist as female primary cells. Polymorphism for HaeIII sites of the amplified Xist cDNA revealed that both Xist(a) and Xist(b) alleles were expressed in differentiated cell population. These results indicate that X inactivation occurred in a random process during differentiation of OTF9 hybrid cells in vitro.