<i>MAYEX</i>is an old long noncoding RNA recruited for X chromosome dosage compensation in a reptile

Abstract

Long noncoding RNAs (lncRNAs) are essential regulatory elements of sex chromosomes that act to equalize gene expression levels between males and females. <i>XIST</i>, <i>RSX</i>, and <i>roX2</i> regulate X chromosomes in placental mammals, marsupials, and <i>Drosophila</i>, respectively. Because the green anole (<i>Anolis carolinensis</i>) shows complete dosage compensation of its X chromosome, we tested whether a lncRNA was involved. We found an ancient lncRNA, <i>MAYEX</i>, that gained male-specific expression more than 89 million years ago. <i>MAYEX</i> evolved a notable association with the acetylated histone 4 lysine 16 (H4K16ac) epigenetic mark and the ability to loop its locus to the totality of the X chromosome to increase expression levels. <i>MAYEX</i> is the first lncRNA in reptiles linked to a dosage compensation mechanism that balances the expression of sex chromosomes.