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Gkountromichos, F.

Publications and source records attributed to Gkountromichos, F..

2 recordsLinked to original sources
bioRxiv2026

Dosage compensation defects due to roX RNA deletion are rescued by recalibration of X/autosome stoichiometry

Metazoa evolved regulatory networks to balance the expression of their sex chromosomes. In Drosophila, males have a single gene-rich X chromosome, whereas females have two. Balanced X/autosome expression is essential for viability, and in male flies is achieved by activation of genes on the X through the male-specific-lethal (MSL) dosage compensation complex (DCC). This ribonucleoprotein assembly contains long, non-coding roX RNAs. To dissect the functional requirements of roX in a cell-based system, we deleted the roX2 gene in male S2 cells and selected two independent lines lacking detectable roX RNA. In the absence of roX, the remaining MSL protein complex was unable to associate with known or newly identified binding sites and thus failed to activate transcription. Surprisingly, the X/autosome expression ratio appeared nevertheless compensated. Cytogenetic and genomic analyses revealed that both roX-deficient cell populations had acquired additional X chromosomes. Apparently, chromosome gains due to mis-segregation made up for the loss of DCC-mediated dosage compensation. Interestingly, ectopic expression of full-length roX2, but not of shortened derivatives, fully restored DCC binding and normalized the karyotype. These findings illustrate that X chromosome dosage compensation is critical for viability even in cultured cells and provide a striking example of rapid evolution under stringent selection. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=83 SRC="FIGDIR/small/707606v1_ufig1.gif" ALT="Figure 1"> View larger version (23K): org.highwire.dtl.DTLVardef@1bbf907org.highwire.dtl.DTLVardef@1da43a9org.highwire.dtl.DTLVardef@903326org.highwire.dtl.DTLVardef@10e3865_HPS_FORMAT_FIGEXP M_FIG C_FIG

molecular biology↗
bioRxiv2023

Physical interaction between MSL2 and CLAMP assures direct cooperativity and prevents competition at composite binding sites

MSL2, the DNA-binding subunit of the Drosophila dosage compensation complex, cooperates with the ubiquitous protein CLAMP to bind MSL recognition elements (MREs) on the X chromosome. We explore the nature of the cooperative binding to these GA-rich, composite se-quence elements in reconstituted naive embryonic chromatin. We found that the cooperativity requires physical interaction between both proteins. Remarkably, disruption of this interaction does not lead to indirect, nucleosome-mediated cooperativity as expected, but to competition. The protein interaction apparently not only increases the affinity for composite binding sites, but also locks both proteins in a defined dimeric state that prevents competition. High Affinity Sites of MSL2 on the X chromosome contain variable numbers of MREs. We find that the cooperation between MSL2/CLAMP is not influenced by MRE clustering or arrangement, but happens largely at the level of individual MREs. The sites where MSL2/CLAMP bind strongly in vitro locate to all chromosomes and show little overlap to an expanded set of X-chromosomal MSL2 in vivo binding sites generated by CUT&RUN. Apparently, the intrinsic MSL2/CLAMP cooperativity is limited to a small selection of potential sites in vivo. This restriction must be due to components missing in our reconstitution, such as roX2 lncRNA.

molecular biology↗