The roX genes encode redundant male-specific lethal transcripts required for targeting of the MSL complex

Abstract

The roX1 and roX2 genes of Drosophila produce malespeci®c non-coding RNAs that co-localize with the Male-Speci®c Lethal (MSL) protein complex. This complex mediates up-regulation of the male X chromosome by increasing histone H4 acetylation, thus contributing to the equalization of X-linked gene expression between the sexes. Both roX genes overlap two of~35 chromatin entry sites, DNA sequences proposed to act in cis to direct the MSL complex to the X chromosome. Although dosage compensation is essential in males, an intact roX1 gene is not required by either sex. We have generated¯ies lacking roX2 and ®nd that this gene is also non-essential. However, simultaneous removal of both roX RNAs causes a striking male-speci®c reduction in viability accompanied by relocation of the MSL proteins and acetylated histone H4 from the X chromosome to autosomal sites and heterochromatin. Males can be rescued by roX cDNAs from autosomal transgenes, demonstrating the genetic separation of the chromatin entry and RNA-encoding functions. Therefore, the roX1 and roX2 genes produce redundant, male-speci®c lethal transcripts required for targeting the MSL complex.

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

“…One of the primary functions of the MSL complex is thought to be acetylation of histone H4 at lysine 16 (H4Ac16), a modification associated with increased expression and attributable to MOF, a histone acetyltransferase (Akhtar and Becker 2000;Smith et al 2000). Two noncoding RNAs, roX1 and roX2, are integral components of the MSL complex and necessary for exclusive binding to the X chromosome (Meller and Rattner 2002). Simultaneous mutation of both roX genes causes male lethality, but mutation of a single roX gene is without phenotype.…”

Worm chromosomes call for recognition!

“…In spite of their lack of sequence similarity, roX1 and roX2 produce functionally redundant components of the fly dosage compensation complex (also known as the MSL complex). (10) When moved to an autosome both roX genes will sometimes direct localization of the MSL complex to chromatin in cis, reminiscent of Xist activity on mammalian autosomes. However, translocations of the Drosophila X chromosome to autosomes attract the MSL complex but fail to direct spreading of these proteins into autosomal chromatin.…”

“…(11) roX transcripts produced from an autosome may travel in trans to the X chromosome, and roX1 À roX2 À males are rescued by autosomal insertions of roX transgenes, further distinguishing the properties of the mammalian Xist and Drosophila roX RNAs. (10) Targeting to the fly X chromosome combines elements of Fig. 1B, as multiple cis-acting marks are present.…”

A male‐specific effect of dominant‐negative Fos

“…We investigated genetic interactions between the msl and mle mutations, and vg-Fbz, which shows a male-limited wing phenotype. We also tested interactions with an X chromosome containing loss of function for both the rox1 and roX2 redundant loci (Meller and Rattner, 2002;Deng et al, 2005).…”

“…Finally, we examined if vg-Fbz interacted with an X chromosome deficient for roX1 and roX2 functions: roX1 ex21A Df(1)52 (Deng et al, 2005). In this experiment, the lethality associated with roX2 deficiency (Df(1)52) was covered with a rescuing transgene (wϩ4⌬4.3) that does not contain roX2 (Meller and Rattner, 2002). Despite a loss of function for both roX loci, male escapers are observed in this genotype, because the roX1 ex21A allele is not null (V. Meller, personal communication).…”