roXRNAs Are Required for Increased Expression of X-Linked Genes inDrosophila melanogasterMales

Abstract

The male-specific lethal (MSL) ribonucleoprotein complex is necessary for equalization of X:A expression levels in Drosophila males, which have a single X chromosome. It binds selectively to the male X chromosome and directs acetylation of histone H4 at lysine 16 (H4Ac16), a modification linked to elevated transcription. roX1 and roX2 noncoding RNAs are essential but redundant components of this complex. Simultaneous removal of both roX RNAs reduces X localization of the MSL proteins and permits their ectopic binding to autosomal sites and the chromocenter. However, the MSL proteins still colocalize, and low levels of H4Ac16 are detected at ectopic sites of MSL binding and residual sites on the X chromosome of roX1 À roX2 À males. Microarray analysis was performed to reveal the effect of roX1 and roX2 elimination on X-linked and autosomal gene expression. Expression of the X chromosome is decreased by 26% in roX1 À roX2 À male larvae. Enhanced expression could not be detected at autosomal sites of MSL binding in roX1 À roX2 À males. These results implicate failure to compensate X-linked genes, rather than inappropriate upregulation of autosomal genes at ectopic sites of MSL binding, as the primary cause of male lethality upon loss of roX RNAs.

Coordinated Regulation of Heterochromatic Genes inDrosophila melanogasterMales

“…Autosomal genes on the second and third chromosomes remain unchanged, but expression from the fourth chromosome actually increases when MSL2 is expressed in roX1 roX2 females ( Figure S2). Although unexpected, this increase is consistent with the accumulation of low levels of H4Ac16 at sites of mislocalized MSL proteins (Deng and Meller 2006). We conclude that ectopic binding of the MSL proteins to the fourth chromosome does not cause repression of fourth-linked genes in roX1 roX2 males.…”

“…roX1 roX2 males rarely survive past the third larval instar, but males mutated for a single roX gene are developmentally normal with full survival. In support of this, the localization of the MSL proteins on the polytenized X chromosome of roX2 and wild-type males appears identical on chromosome preparations (Deng and Meller 2006). An overall reduction in X-linked gene expression was observed in the roX1 roX2 male larvae (Deng and Meller 2006).…”

“…In support of this, the localization of the MSL proteins on the polytenized X chromosome of roX2 and wild-type males appears identical on chromosome preparations (Deng and Meller 2006). An overall reduction in X-linked gene expression was observed in the roX1 roX2 male larvae (Deng and Meller 2006). However, to our surprise, expression of genes situated on the small fourth chromosome was also reduced by $50% in roX1 roX2 males ( Figure 1A).…”

“…In roX1 roX2 males the MSL proteins bind at ectopic autosomal sites and the chromocenter. Microarray expression analysis of roX1 roX2 (null for roX function) and roX2 (control) male larvae confirmed that roX RNA is required for full expression of X-linked genes in males (Deng and Meller 2006).…”

Imprinting of the Y Chromosome Influences Dosage Compensation inroX1 roX2 Drosophila melanogaster

“…MSL binding in nuclei from males carrying partial loss-of-function roX1 roX2 chromosomes suggests a direct relationship between the recovery of male escapers and the amount of MSL protein localizing to the X chromosome (Deng et al 2005). A global decrease in X-linked gene expression is detected in roX1 roX2 males (Deng and Meller 2006). These studies indicate that roX activity is required for X recognition or stable association of the MSL complex with the X chromosome.…”