Developmentally regulated alternative splicing of transcripts from the Drosophila homeotic gene Antennapedia can produce four different proteins.

Antennapedia (Antp) is a Drosophila homeotic gene that controls differentiation of the thoracic segments. Antp transcripts are produced from either of two promoters that are independently regulated in temporally and spatially distinct patterns. In addition, Antp transcripts utilize either of two major polyadenylation sites. Antp primary transcripts contain the same protein coding sequences. Alternative RNA splicing at two positions within the primary transcripts produces mRNAs that can encode four slightly different Antp proteins. Different classes of alternatively spliced transcript predominate early and late in Drosophila development, indicating that the Antp gene is regulated by the processing of its transcripts as well as by controlling their transcription. Alternative splicing appears to be independent of which promoter and which polyadenylation site is used.