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Compensation Culture RESEARCH HIGHLIGHTS GENE REGULATION rather than intergenic regions, were In larvae, the recruitment of MSL1 favoured by the complex, which did not rely solely on transcription Compensation bound most strongly to the 3′ end of on the X chromosome. Moreover, the transcription units. The authors many genes on the X chromosome culture proposed a model in which indi- seemed to be dosage compensated DOI: Dosage compensation ensures that vidual genes that are under selective without direct MSL1 binding. The 10.1038/nrg1867 there are equal levels of X-linked pressure to equalize dosage between authors therefore suggested that the gene products in males and females. the sexes have evolved targeting sig- MSL complex might also regulate URLs In Drosophila melanogaster, this is nals to attract the MSL complex. transcription of X-linked genes at a achieved by doubling the transcript Peter Park, Mitzi Kuroda and distance in larvae. levels of X-linked genes in males. colleagues also determined the Taken together, these papers raise The process requires the association X-chromosome-specific binding new questions about dosage-com- on the X chromosomes of the male- pattern of the MSL complex in two pensation selectivity and highlight specific lethal (MSL) complex, or male cell lines and in embryos, again the need for further investigation dosage-compensation complex. Now, using high-resolution genomic tiling into selectivity determinants, while three independent reports present arrays. Similarly to Becker’s group, helping to redefine current models the results of chromosome-wide the authors found that the MSL com- of dosage compensation. Given that analyses of several MSL proteins. plex recognizes and preferentially the vertebrate X chromosome has Using chromatin immunoprecipita- binds to genes rather than intergenic also been shown to be subject to tion combined with high-throughput regions; the binding is also biased activating dosage compensation, DNA microarray detection, the towards the 3′ end of the transcrip- lessons that have been learned from chromosome-wide binding of the tion units. The same gene sequences studying fruitflies could also help to D. melanogaster MSL complex to can be clearly bound or unbound by understand dosage compensation in the single male X chromosome is the MSL complex, depending on cell other species. detailed with unprecedented resolu- type, indicating that MSL targeting Sharon Ahmad, Assistant Editor, tion, providing new insights into the cannot be explained by sequence Nature Reviews Molecular Cell Biology dosage-compensation process. alone. The authors proposed that the ORIGINAL RESEARCH PAPERS Peter Becker’s group investigated MSL complex selectively targets most Gilfillan, G. D. et al. Chromosome-wide gene- how the MSL complex identifies X-linked genes, but only within the specific targeting of the Drosophila dosage compensation complex. Genes Dev. 17 March 2006 and binds the X chromosome in context of active transcription. (doi:10.1101/gad.1399406) | Alekseyenko, A. A. fly embryos using high-resolution Asifa Akhtar and colleagues et al. High-resolution ChIP–chip analysis reveals genomic tiling arrays. They found mapped the distribution of MSL1, that the Drosophila MSL complex selectively identifies active genes on the male that just over half the annotated a component of the MSL complex, X chromosome. Genes Dev. 17 March 2006 genes on the X chromosome were in D. melanogaster embryos and (doi:10.1101/gad.100206) | Legube, G. et al. bound by the complex. Preferred larvae using an expression array X-chromosome-wide profiling of MSL-1 distribution and dosage compensation in targets were essential genes, and that represented more than 10,000 Drosophila. Genes Dev. 17 March 2006 the greatest compensation was seen annotated fly genes. They found (doi:10.1101/gad.377506) FURTHER READING Schübeler, D. Dosage for genes that bound high levels of that most MSL1-bound genes were compensation in high resolution: global up- the MSL complex. Notably, genes, expressed early in embryogenesis. regulation through local recruitment. Genes Dev. 17 March 2006 (doi:10.1101/gad.1423006) “…helping to redefine current mod- els of dosage compensation.” NATURE REVIEWS | GENETICS VOLUME 7 | MONTH 2006 | 1 © 2006 Nature Publishing Group .
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