Schauer, T. et al. Cell Rep. 5, 271–282 (2013).

An organism's development depends on carefully orchestrated cell type–specific gene expression, which is regulated largely by chromatin structure. To fully appreciate the role that chromatin domains play in this process, Schauer et al. developed CAST-ChIP (chromatin affinity purification from specific cell types by chromatin immunoprecipitation). They focused on the fly brain and used the cell type–specific expression of a tagged transgene in combination with affinity-tag purification to enrich enough cells to profile polymerase II binding and histone H2A.Z positions in glia and neurons. The polymerase II data yielded ∼1,500 genes expressed specifically in these cell types. The authors also saw that H2A.Z shows no cell type–specific distribution and thus marks universally active chromatin. CAST-ChIP will allow the exploration of chromatin structures and their effect on gene expression in complex tissues.