Differential and inefficient splicing of a broadly expressed Drosophila erect wing transcript results in tissue-specific enrichment of the vital EWG protein isoform

In this report, we document an unusual mode of tissue-enriched gene express ion that is primarily mediated by alternative and inefficient splicing. We have analyzed posttranscriptional regulation of the Drosophila erect wing g ene, which provides a vital neuronal function and is essential for the form ation of certain muscles. Its predominant protein product, the 116-kDa EWG protein, a putative transcriptional regulator, can provide all known erect wing-associated functions. Moreover, consistent with its function, the 116- kDa protein is highly enriched in neurons and is also observed transiently in migrating myoblasts, In contrast to the protein distribution, we observe d that Erect wing transcripts are present in comparable levels in neuron-en riched heads and neuron-poor bodies of adult Drosophila, Our analyses shows that erect wing transcript consists of 10 exons and is alternatively splic ed and that a subset of introns are inefficiently spliced. We also show tha t the 116-kDa EWG protein-encoding splice isoform is head enriched. In cont rast, bodies have lower levels of transcripts that can encode the 116-kDa p rotein and greater amounts of unprocessed erect wing RNA. Thus, the enrichm ent of the 116-kDa protein in heads is ensured by tissue-specific alternati ve and inefficient splicing: and not by transcriptional regulation, Further more, this regulation is biologically important, as an increased level of t he 116-kDa protein outside the nervous system is lethal.