Dorsal-B, a splice variant of the Drosophila factor Dorsal, is a novel Rel/NF-κB transcriptional activator

The Drosophila transcription factor Dorsal, a member of the Rel/NF-kappa B family of proteins, plays a key role in the establishment of dorsoventral polarity in the early embryo and is also involved in the immune response. Here, we present evidence that the primary transcript of dorsal can be alternatively spliced, generating Dorsal-B, a new Rel/NF-kappa B family member. Dorsal and Dorsal-B are identical in the N-terminal region, which comprises both a DNA-binding domain and a dimerization domain. However, Dorsal-B lacks the nuclear localization signal located at the end of the Rel domain of Dorsal and is totally divergent in the C-terminal portion. Although Dorsal-B by itself is not able to induce the expression of a kappa B-controlled Luciferase reporter gene, we demonstrate that its C-terminal portion has transactivating properties. Analysis of the dorsal-B expression pattern indicates that the splicing is tissue-specific and excludes a putative role in early embryogenesis. However, dorsal-B synthesis is enhanced upon septic injury, and this challenge induces a nuclear accumulation of the protein in fat body cells suggesting that it may be involved in the immune response. (C) 1999 Elsevier Science B.V. All rights reserved.