RNA-on-X 1 and 2 in Drosophila melanogaster fulfill separate functions in dosage compensation

PLoS Genet. 2018 Dec 10;14(12):e1007842. doi: 10.1371/journal.pgen.1007842. eCollection 2018 Dec.


In Drosophila melanogaster, the male-specific lethal (MSL) complex plays a key role in dosage compensation by stimulating expression of male X-chromosome genes. It consists of MSL proteins and two long noncoding RNAs, roX1 and roX2, that are required for spreading of the complex on the chromosome and are redundant in the sense that loss of either does not affect male viability. However, despite rapid evolution, both roX species are present in diverse Drosophilidae species, raising doubts about their full functional redundancy. Thus, we have investigated consequences of deleting roX1 and/or roX2 to probe their specific roles and redundancies in D. melanogaster. We have created a new mutant allele of roX2 and show that roX1 and roX2 have partly separable functions in dosage compensation. In larvae, roX1 is the most abundant variant and the only variant present in the MSL complex when the complex is transmitted (physically associated with the X-chromosome) in mitosis. Loss of roX1 results in reduced expression of the genes on the X-chromosome, while loss of roX2 leads to MSL-independent upregulation of genes with male-biased testis-specific transcription. In roX1 roX2 mutant, gene expression is strongly reduced in a manner that is not related to proximity to high-affinity sites. Our results suggest that high tolerance of mis-expression of the X-chromosome has evolved. We propose that this may be a common property of sex-chromosomes, that dosage compensation is a stochastic process and its precision for each individual gene is regulated by the density of high-affinity sites in the locus.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Cycle / genetics
  • Dosage Compensation, Genetic*
  • Drosophila Proteins / genetics*
  • Drosophila melanogaster / cytology
  • Drosophila melanogaster / genetics*
  • Female
  • Gene Expression Regulation
  • Genes, Insect
  • Male
  • Models, Genetic
  • Mutation
  • RNA, Long Noncoding / genetics
  • RNA-Binding Proteins / genetics*
  • Stochastic Processes
  • Testis / metabolism
  • Transcription Factors / genetics*
  • X Chromosome / genetics


  • Drosophila Proteins
  • Pabp2 protein, Drosophila
  • RNA, Long Noncoding
  • RNA-Binding Proteins
  • Transcription Factors
  • roX1 protein, Drosophila

Grants and funding

This work was supported by grants from the Knut and Alice Wallenberg foundation (2014.0018), the Swedish Research Council (2016-03306) and Swedish Cancer Foundation (CAN 2017/342) to JL. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.