is an old long noncoding RNA recruited for X chromosome dosage compensation in a reptile.

Long noncoding RNAs (lncRNAs) are essential regulatory elements of sex chromosomes that act to equalize gene expression levels between males and females. , , and regulate X chromosomes in placental mammals, marsupials, and , respectively. Because the green anole () shows complete dosage compensation of its X chromosome, we tested whether a lncRNA was involved. We found an ancient lncRNA, , that gained male-specific expression more than 89 million years ago. 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. is the first lncRNA in reptiles linked to a dosage compensation mechanism that balances the expression of sex chromosomes.