ELEMENTS CONTROLLING FOLLICULAR EXPRESSION OF THE S36 CHORION GENE DURING DROSOPHILA OOGENESIS

An 84-bp proximal regulatory region (PRR) of the Drosophila melanogast er s36 chorion gene is sufficient for directing proper temporal and sp atial expression of a reporter gene in three domains of the follicle: anterior, posterior, and main body. Here we show that the fidelity of PRR-directed s36 expression is dependent on the proper dorsal-ventral differentiation of the follicular epithelium, which requires the Droso phila epidermal growth factor receptor homolog. Transgenic analysis of site-directed mutants of the PRR suggests that s36 expression is regu lated by the concerted action of multiple positive activators. Several cis-acting transcriptional elements have been identified: some appear to function in a quantitative manner, while others either are essenti al or appear to regulate expression in particular spatial domains. The approximate locations of these regulatory elements have been defined; some map within sequences that are strongly conserved in widely diver gent dipteran species. In fact, the PRR analog of the medfly Ceratitis capitata Ccs36 gene directs expression in a manner similar to the D. melanogaster s36 PRR. We propose a model for transcriptional regulatio n of s36 based on the prechoriogenic polarization of the follicular ep ithelium that surrounds the developing egg chamber.