Redundant enhancer elements guide beta 1 tubulin gene expression in apodemes during Drosophila embryogenesis.

During Drosophila embryogenesis, the beta 1 tubulin gene (beta Tub56D) is expressed in the CNS and PNS as well as in the apodemes. In this report we determine the regulation of beta 1 tubulin gene expression during formation of the attachment sites of the somatic muscles, the apodemes. The process was analysed in transgenic flies carrying beta 1 enhancer-hsp70 promoter-lacZ fusion constructs. Expression is first detected at late stage 13 and remains until hatching. By deletion analysis of the intron we identified a 14-bp element present in three copies. This element represents a classical enhancer, as it acts on a heterologous promoter. Separate fragments containing the respective elements yield nearly identical expression patterns, and no cooperativity was observed between the three copies. Thus, the expression of the beta 1 tubulin gene in the apodemes is under control of redundant enhancer elements. Double staining for beta 1 tubulin gene expression in apodemes and for beta 3 tubulin gene expression in muscles allowed us to correlate apodeme and muscle formation. Cells of the apodemes that are in contact with their corresponding muscles show expression of the reporter gene as monitored by antibody staining.