Experimental outline. (A) Map of the chicken lysozyme locus (+10 kb to -10 kb relative to the transcription start) and its position in the mouse X-chromosome. The clys and the gas41 gene in the transgene are indicated as white boxes. The direction of transcription is depicted as a horizontal arrow. DNaseI hypersensitive sites (DHS) observed in macrophages are indicated as vertical arrows, with black arrows indicating the position of cis-regulatory elements. Cis-elements are depicted as gray boxes, with E standing for enhancer. (B) Schematic outline of macrophage differentiation. (C) Experimental strategy.