Genetic dissection of the learning/memory gene dunce of Drosophila melanogaster.

The dunce (dnc) gene of Drosophila melanogaster codes for cAMP phosphodiesterase (PDE) and is required for normal learning/memory and for female fertility. The expression of the gene is elevated in mushroom bodies, brain structures implicated in olfactory learning and memory. In this study several chromosomal deletions and inversions that remove increasingly larger portions of the dnc gene from its 5' end and progressively more of the five known transcription start sites (tss) were used to assess the functions of the various transcriptional units. Surprisingly, the dnc PDE activity, female fertility, mushroom body expression, learning, and memory were unaffected by the removal of tss1 and tss2. tss3 was required for elevated mushroom body expression but not for female fertility nor initial learning. tss4 contributed to learning and the female fertility function, whereas tss5 contributed to female fertility. The results indicate that the structural complexity of the gene is of biological significance, with individual transcriptional units serving different biological functions.