MSL cis-spreading from roX gene up-regulates the neighboring genes

The male-specific lethal (MSL) complex in Drosophila melanogaster paints the male X chromosome in a manner that is both cis and trans to induce 2-fold hypertranscription of the X chromosome. To characterize the upregulation of gene expression by MSL cis-spreading, we measured the expressional change of neighboring genes by microarray when the genes were bound by MSL complexes that spread from an autosomal roX transgene. Genes within a 200kb region that includes roX transgenes were upregulated concurrently with MSL cis-spreading. Conversely, there was almost no expressional change in genes from other regions. RT-PCR and ChIP analyses confirmed that the approximately 2-fold gene hypertranscription was due to MSL cis-spreading. We also demonstrated that upregulation of the neighboring gene could rescue haplo-insufficient phenotypes of the Minute mutant, such as short bristle, delayed adult eclosion and decreased viability. These results indicate that the hypertranscription by MSL cis-spreading is a general mechanism that occurs in several tissue types. Our molecular and genetic data suggest that cis-spreading of the MSL complex from high-affinity sites including the roX gene results in upregulation of the neighboring genes, which are targets for dosage compensation in the male X chromosome.