roX

roX refers to two X-linked noncoding RNA genes, roX1 and roX2, in Drosophila melanogaster. The roX RNAs encode long noncoding transcripts that are integral components of the male dosage compensation system and are among the best-studied examples of noncoding RNA guiding chromatin modification.

Functionally, roX1 and roX2 are incorporated into the male-specific lethal (MSL) complex and are required for its targeting to the X chromosome. The MSL complex promotes histone H4 lysine 16 acetylation (H4K16ac), which increases transcription from the single male X to balance expression with females that have two X chromosomes.

Genetic evidence indicates that roX1 and roX2 have overlapping, partially redundant roles. Loss of one roX RNA can be tolerated, but simultaneous disruption of both roX1 and roX2 undermines dosage compensation and leads to defects or lethality in males, underscoring their essential function.

RoX transcripts are present in Drosophila species, and although their sequences diverge, their function as guiding RNAs for the MSL complex is conserved. The roX RNAs localize to the X chromosome and help stabilize the MSL complex on active chromatin, facilitating targeted upregulation of the male X.

Origin of the name: roX stands for “RNA on X.” The study of roX1 and roX2 has contributed to understanding how noncoding RNAs participate in chromatin regulation and dosage compensation.