As the only class I helix-loop-helix transcription factor in Drosophila, 
Daughterless (Da) has generally been regarded as a ubiquitously expressed 
binding partner for other developmentally regulated bHLH transcription factors. 
From analysis of a novel tissue-specific allele, da(lyh), we show that da 
expression is not constitutive, but is dynamically regulated. This 
transcriptional regulation includes somatic ovary-specific activation, 
autoregulation and negative regulation. Unexpectedly, the diverse functions of 
da may require that expression levels be tightly controlled in a cell and/or 
tissue-specific manner. Our analysis of da(lyh) identifies it as the first 
springer insertion that functions as an insulating element, with its disruptive 
activity mediated by the product of a fourth chromosome gene, Suppressor of lyh 
[Su(lyh)].