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Science. 2006 Jun 16;312(5780):1653-5.

The Xist RNA gene evolved in eutherians by pseudogenization of a protein-coding gene.

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Laboratoire de Biométrie et Biologie Evolutive (UMR 5558), CNRS and Université Lyon 1, 16 rue Raphaël Dubois, 69622 Villeurbanne Cedex, France.


The Xist noncoding RNA is the key initiator of the process of X chromosome inactivation in eutherian mammals, but its precise function and origin remain unknown. Although Xist is well conserved among eutherians, until now, no homolog has been identified in other mammals. We show here that Xist evolved, at least partly, from a protein-coding gene and that the loss of protein-coding function of the proto-Xist coincides with the four flanking protein genes becoming pseudogenes. This event occurred after the divergence between eutherians and marsupials, which suggests that mechanisms of dosage compensation have evolved independently in both lineages.

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