X-chromosome inactivation machinery (XCI machinery)

The X-chromosome inactivation (XCI) machinery is a complex epigenetic system responsible for the transcriptional silencing of one of the two X chromosomes in female mammals, a process essential for dosage compensation between the sexes (Gendrel & Heard, 2014). This machinery is primarily driven by the long non-coding RNA XIST, which coats the inactive X chromosome (Xi) and recruits various repressive factors, including Polycomb Repressive Complexes (PRC1/2), histone deacetylases, and DNA methyltransferases (Lyst & Bird, 2015). In the context of Rett syndrome, a neurodevelopmental disorder caused by mutations in the X-linked MECP2 gene, the XCI machinery has emerged as a novel therapeutic target. By pharmacologically or molecularly disrupting the maintenance of the Xi, researchers aim to reactivate the dormant, wild-type MECP2 allele to restore functional protein levels (Przanowski et al., 2018). Current experimental strategies include the use of antisense oligonucleotides (ASOs) to degrade XIST or small molecules to inhibit the epigenetic modifiers that sustain the silent state (Bhatnagar et al., 2014). However, a major challenge in targeting this machinery is achieving gene-specific reactivation to avoid the toxic effects associated with the global overexpression of other X-linked genes.

Other names

X-reactivation machineryXi reactivation factorsX-chromosome inactivation (XCI) complexXIST-mediated silencing complexInactive X chromosome (Xi) regulators

The therapeutic approach involves the inhibition of the X-chromosome inactivation (XCI) machinery to reverse the transcriptional silencing of the inactive X chromosome (Xi). This is achieved by targeting the long non-coding RNA XIST for degradation or by inhibiting epigenetic 'locks' such as DNA methyltransferases (DNMTs) and histone deacetylases (HDACs), thereby allowing the expression of the dormant wild-type MECP2 allele on the Xi.