RNA nucleation by MSL2 induces selective X chromosome compartmentalization

Area of Science:

• Genetics
• Molecular Biology
• Epigenetics

Background:

• X chromosome dosage compensation in Drosophila relies on the male-specific lethal (MSL) complex and roX RNAs.
• The MSL complex associates with the X chromosome to increase gene expression in males.
• Existing models propose high-affinity sites (HAS) on DNA dictate MSL complex specificity, but HAS are also found on autosomes.

Purpose of the Study:

• To investigate the role of the MSL2 C-terminal domain (CTD) and roX RNAs in X chromosome targeting.
• To elucidate the mechanism stabilizing MSL complex association with the X chromosome.
• To determine if roX-MSL2 interactions are essential for dosage compensation in vivo.

Main Methods:

• Investigated MSL2 CTD sensitivity to roX RNAs for X chromosome recruitment.
• Analyzed the condensed state formed by roX RNAs and MSL2 CTD.
• Performed functional analyses in Drosophila and mammalian cells.

Main Results:

• The MSL2 CTD's recruitment to the X chromosome is sensitive to roX non-coding RNAs.
• roX RNAs and the MSL2 CTD form a stable condensed complex.
• This interaction is vital for dosage compensation in both Drosophila and mammalian systems.
• Ectopic dosage compensation was induced in mammalian cells by replacing MSL2 CTD and expressing roX RNAs.

Conclusions:

• The condensing interaction between roX RNAs and the MSL2 CTD is the primary factor for X chromosome compartmentalization.
• This mechanism ensures specific targeting of the MSL complex to the X chromosome for dosage compensation.
• The findings reveal a novel mechanism for epigenetic regulation and gene dosage control.