Structure and expression of the egg-laying hormone gene family in Aplysia.

Transcription of the egg-laying hormone (ELH) gene family was examined by characterizing homologous cDNA clones from abdominal ganglion and atrial gland cDNA libraries. All cDNAs contain an exon that spans the coding region (exon III) and one or two additional exons. The tissue-specific expression of the ELH gene family was confirmed by the observation that exon III encodes the ELH precursor protein in the bag cell transcripts and either the A or B precursor proteins in the atrial gland transcripts. The cDNA clones also contain 5' untranslated exons not present in the previously isolated genomic clones. One type of transcript has a 40-base pair segment, designated exon I, contiguous with exon III. A second type of transcript has an additional 149 base pairs of DNA, designated exon II, located between exons I and III. Several genomic clones containing exons I and II were isolated. DNA sequence analysis reveals that exons I and II are directly linked and that they are separated from exon III by an intervening sequence of at least 5 kilobases (kb). Consensus sequences for a putative promotor region and also for RNA splicing and polyadenylation were identified. From this work we can describe a prototype ELH gene complete with identified sequences necessary for the proper initiation of transcription and the subsequent processing of the transcript.