Grant: Operating Grant

Human females have two X chromosomes, while males have a single X chromosome and the sex-determining Y chromosome. The X chromosome contains over a thousand genes, so in order to avoid a dosage difference between males and females, one of the two X chromosomes in females is inactivated. We study this inactivation process in order to understand how genes can be silenced during mammalian development. We have identified that the critical initiating factor in this inactivation is expression of a gene, called XIST. Unlike most genes XIST does not encode a protein, but rather functions in the nucleus of the cell as a functional RNA. This RNA is the only RNA that is only expressed from the X chromosome that is silenced, and it 'coats' the silenced X chromosome, causing the other genes on that chromosome to become inactive. Our experiments will show how the RNA can silence genes, coat the chromosome, and alter the structure of the coated chromosome. To address these questions we will use cell lines that make the RNA when treated with antibiotic and use smaller parts of the RNA to identify which regions are critical for functionality. We can then identify the proteins that interact with the RNA to understand how RNAs can cause silencing. There are many other potentially functional RNAs in humans, and our work will lead to new understanding of the function of these RNAs.