Targeting the dosage compensation complex

Three independent research papers in the April 1 issue of G&D detail the chromosome-wide binding of the Drosophila dosage compensation complex (DCC) to the single male X chromosome, shedding new light on the mechanism of DCC targeting.

Dosage compensation is the equalization of X-linked gene expression between males (which have one X chromosome in flies) and females (which have two X chromosomes in flies). The DCC is responsible for increasing transcription of the single male X chromosome two-fold. But how the DCC distinguishes the X chromosome from the other 7chromosomes chromosomes in the nucleus has remained a mystery.

As published in G&D, the labs of Drs. Mitzi Kuroda and Peter Park (Harvard Medical School), Peter Becker (University of Munchen) and Asifa Akhtar (EMBL) have usedused used chromatin immunoprecipitation combined with high-throughput DNA microarrays (ChIP on Chip) to map DCC binding along the X chromosome in various biological contexts.

Taken together, the papers show striking recruitment of the DCC to coding sequences, rather than upstream regulatory regions on the X chromosome, also excluding domain-wide targeting of the complex. The studies lead to new questions about the selectivity of dosage compensation. Because the majority of active genes (but not all!) are identified amongst the large amount of noncoding DNA along the X chromosome, important selectivity determinants remain to be uncovered.

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