Regulation of the complex pattern of sevenless expression in the developing Drosophila eye

The sevenless gene encodes a cell surface receptor that has protein-tyrosine kinase activity and is expressed in a highly specific and complex pattern in the developing Drosophila eye. We have coupled the sevenless promoter to the reporter gene lacZ and have examined the pattern of beta-galactosidase expression in the developing eyes of transgenic larvae. Our results indicate that the dynamic pattern of sevenless protein expression is regulated transcriptionally. Promoter sequences located 5' of the coding region are insufficient for the wild-type level of gene expression but appear to be able to confer the correct pattern of expression. In contrast, enhancer sequences within the body of the gene can confer both the correct pattern and a normal level of expression on either the sevenless promoter or heterologous promoters. Thus the complex pattern of sevenless expression is redundantly encoded within proximal promoter sequences and enhancer elements internal to the gene but relies on these enhancer sequences for correct quantitative expression.