Multiple, compensatory regulatory elements specify spermatocyte-specific expression of the Drosophila melanogaster hsp26 gene.

The hsp26 gene of Drosophila melanogaster is expressed in six tissues during development and in a tissue-general response to heat shock. To be able to compare tissue-specific and heat-induced mechanisms of hsp26 expression, we have begun an analysis of the sequences involved in the spermatocyte-specific expression of the hsp26 gene by using germ line transformation. hsp26 mRNA synthesized in the spermatocytes has the same start site as sites previously demonstrated for nurse cell-specific and heat-induced mRNAs. Three regions of the hsp26 gene (nucleotides -351 to -135, -135 to -85, and +11 to +632) were able to stimulate spermatocyte-specific expression when fused with promoter sequences (nucleotides -85 to +11) that alone were insufficient to stimulate expression. These stimulatory regions appear to contain elements that provide redundant functions. While each region was able to stimulate expression independently, the deletion of any one region from a construct was without consequence as long as another compensatory region(s) was still present. There must reside, at a minimum, two independent spermatocyte-specifying elements within the sequences that encompass the three stimulatory regions and the promoter. At least one element is contained within sequences from -351 to -48. This region, in either orientation, can stimulate spermatocyte-specific expression from a heterologous promoter. A second element must reside in sequences from -52 to +632, since these sequences are also sufficient to direct spermatocyte-specific expression.