Non-canonical role of roX RNA in X-chromosome targeting

• Applicant: Professor Dr. Peter Burkhard Becker
• Subject Area: General Genetics and Functional Genome Biology ; Cell Biology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 524230739

The process of X chromosome dosage compensation in Drosophila melanogaster assures that genomes of both sexes are expressed similarly. Male flies can only live if the transcription of genes on their single X chromosome is boosted in the two-fold fange. Exploring the mechanistic underpinnings of this highly evolved process continues to uncover fundamental principles of genome regulation. The activation of X chromosomal genes in male flies is achieved by the dosage compensation complex (DCC), a multi-enzyme assembly consisting of five male-specific-lethal (MSL) proteins and long, non-coding roX RNA. The initial, highly selective binding of the DCC to the X chromosome is key to faithful dosage compensation. Impairment of this process leads to indiscriminate chromosome binding, which is lethal for affected male flies. The role of roX RNA and the helicase MLE that mediates assembly of this lncRNA into the DCC is poorly understood. The DCC is actually one of the very few chromatin-bound lncRNPs, for which all RNA and protein subunits are known, thus providing a huge opportunity to investigate the function of a lncRNA in detail. We recently discovered an important role for roX2 RNA in X chromosome selectivity. Curiously, the most intuitive functions for such RNAs appear not to apply to roX. RoX apparently does not read out DANN sequence by triple-helix or R-loop formation. RoX also does not function as a scaffold to facilitate complex formation, since the MSL proteins can from active complexes in the absence of RNA. We also found that the specific binding of the DCC to the X chromosome in the presence of roX correlated with the adoption of a tight-binding mode, documented by unusually long residence times in FRAP experiments. We seek to uncover novel principles and underlying molecular mechanism, through which roX RNAs promote the robust and exclusive binding of the MSL complex to the X chromosome, and which underlie the ‘tight-binding’ state of the DCC on the X chromosome.

• DFG Programme: Research Grants