Enhanced chromatin accessibility of the dosage compensated Drosophila male X chromosome requires the CLAMP zinc finger protein [START-SEQ]

The essential process of dosage compensation is required to equalize gene expression of X-chromosome genes between males (XY) and females (XX). In Drosophila, the conserved Male-specific lethal (MSL) histone acetyltransferase complex mediates dosage compensation by increasing transcript levels from genes on the single male X-chromosome approximately two-fold. Consistent with its increased levels of transcription, the male X-chromosome has enhanced chromatin accessibility, distinguishing it from the autosomes. Here, we demonstrate that the non-sex specific CLAMP (Chromatin-linked adaptor for MSL proteins) zinc finger protein that recognizes GA-rich sequences genome-wide promotes the specialized chromatin environment on the male X-chromosome. In contrast, MSL complex is not required for global male X-chromosome chromatin accessibility, and instead promotes chromatin accessibility just at its highest-occupancy sites. Overall, our results support a model where synergy between the global increases in accessibility promoted by CLAMP and the local effects of MSL complex create a specialized chromatin domain on the male X-chromosome. Drosophila S2 and Kc cells were evaluated using Start RNA sequencing (Start-seq) following a 6-day RNAi treatment of gfp (control) or clamp dsRNA. Three biologigal replicates were performed for each treatment.