The daughterless (da) gene in Drosophila functions in the regulation of at least 
three significant developmental pathways: sex determination, neurogenesis and 
oogenesis. As a member of the helix-loop-helix (HLH) family of DNA binding 
proteins, the da gene product appears to act as a transcription factor. Based on 
the genetic and molecular characterization of da, it has been proposed that the 
da protein (Da) functions as a generic member of this family, serving throughout 
development as a necessary binding partner for an assortment of other HLH 
proteins. As a result of temporally and/or spatially restricted expression, 
these binding partners would provide some regulatory specificity to the 
functional transcription complex. In order to participate in this way in the 
regulation of multiple genes, Da must be expressed in numerous times and places 
during development. Using anti-Da antibodies, we validate two predictions of 
this scenario of Da function: (1) Da protein is not only nuclear localized, but 
also associated with chromosomes in vivo; and (2) Da protein is widely 
distributed, both spatially and temporally, throughout development. With regard 
to the essential role of maternal da+ in progeny sex determination, little, if 
any, Da protein is synthesized in the maternal germline. This suggests that the 
female-specific germline function of da+ is provided to the zygote as maternally 
synthesized RNA that becomes translated early in embryogenesis.