Dual sex-specific functions ofDrosophilaUpstream of N-ras in the control of X chromosome dosage compensation

Abstract

Dosage compensation in Drosophila melanogaster involves the assembly of the MSL-2-containing dosage compensation complex (DCC) on the single X chromosome of male flies. Translational repression of msl-2 mRNA blocks this process in females. Previous work indicated that the ubiquitous protein Upstream of N-ras (UNR) is a necessary co-factor for msl-2 repression in vitro. Here, we explore the function of UNR in vivo. Hypomorphic Unr mutant flies showed DCC assembly on high-affinity sites in the female X chromosomes, confirming that UNR inhibits dosage compensation in female flies. Unexpectedly, male mutant flies and UNRdepleted SL2 cells showed decreased DCC binding to the X chromosome, suggesting a role for UNR in DCC assembly or targeting. Consistent with this possibility, UNR overexpression resulted in moderate loss of DCC from the male X chromosome and predominant male lethality. Immunoprecipitation experiments revealed that UNR binds to roX1 and roX2, the non-coding RNA components of the DCC, providing possible targets for UNR function in males. These results uncover dual sex-specific functions of UNR in dosage compensation: to repress DCC formation in female flies and to promote DCC assembly on the male X chromosome.

Widespread generation of alternative UTRs contributes to sex-specific RNA binding by UNR

“…Sequencing allows the unbiased identification of targets, including non-annotated transcripts and noncoding RNAs. Because UNR binds to the nuclear noncoding RNAs roX1 and roX2 (Patalano et al 2009), in order to identify coding and noncoding poly(A) + transcripts bound by UNR independently of their subcellular distribution, we used total male and female adult extracts for RIP-seq. A RIP experiment including a duplicate with anti-UNR antibodies and one IgG control was performed per sex, and the RNA isolated from the pellet was sequenced (Fig.…”

“…X-chromosome dosage compensation is the process that equalizes the expression of X-linked genes between males (XY) and females (XX), and in Drosophila is achieved by hypertranscription of the single male X chromosome by the dosage compensation complex (DCC), a ribonucleoprotein assembly of at least five proteins (MSL1, MSL2, MSL3, MOF, and MLE) and two noncoding RNAs (roX1 and roX2) (Gelbart and Kuroda 2009). In females, UNR binds to msl2 mRNA and inhibits its translation, contributing to repressing dosage compensation Duncan et al 2006;Patalano et al 2009). Binding of UNR to msl2 mRNA depends on the female-specific RBP Sex-lethal (SXL), which, in addition to recruiting UNR to the 39 UTR of msl2, promotes the retention of a facultative intron in msl2 59 UTR (for review, see Graindorge et al 2011).…”

“…In males, UNR does not bind to msl2 because SXL is absent. In contrast, UNR binds to the roX RNAs in males, and this binding may contribute to promoting DCC recruitment to the X chromosome (Patalano et al 2009). …”

UNR facilitates the interaction of MLE with the lncRNA roX2 during Drosophila dosage compensation

“…9). In males, UNR promotes the targeting of the MSL-DCC to the X-chromosome by a poorly understood mechanism that does not involve translational regulation of MSL proteins 10 . UNR-dependent regulation can be recapitulated in male S2 cells, which express only roX2 (ref.…”

Tapas and RNA in Renaissance Spain

“…However, Unr also has a function in male flies to promote dosage compensation; the mechanism of this positive role is not clear, but may involve interactions with the non-coding roX RNAs that both bind Unr and are part of the DCC. 5 Anna Bremer (Leibniz Institute for Age Research-Fritz Lipmann Institute, Germany) presented data on the RING finger protein TRIM37, whose mutation causes the disorder Mulibrey nanism. 6 Binding of TRIM37 to the 3'UTR of the CCAAT/enhancer-binding protein (C/EBP) α stimulated the translation of a truncated C/EBPα isoform that promotes proliferation.…”