Modular tissue-specific regulation of underpins sexually dimorphic development in .

The ability of a single genome to produce distinct and often dramatically different male and female forms is one of the wonders of animal development. In , most sexually dimorphic traits are controlled by sex-specific isoforms of the () transcription factor, and expression is mostly limited to cells that give rise to sexually dimorphic traits. However, it is unknown how this mosaic of sexually dimorphic and monomorphic organs arises. Here, we characterize the -regulatory sequences that control expression in the foreleg, which contains multiple types of sex-specific sensory organs. We find that separate modular enhancers are responsible for expression in each sexually dimorphic organ. Expression of in the sex comb is co-regulated by two enhancers with distinct spatial and temporal specificities that are separated by a genitalia-specific enhancer. The sex comb-specific enhancer from , a species that primitively lacks sex combs, is not active in the foreleg. Thus, the mosaic of sexually dimorphic and monomorphic organs depends on modular regulation of transcription by dedicated cell type-specific enhancers.