Crustacean hyperglycemic hormone precursor transcripts in the hemocytes of the crayfish Procambarus clarkii: novel sequence characteristics relating to gene splicing pattern and transcript stability

It was demonstrated in a previous study (Wu et al., 2012b) that crustacean hyperglycemic hormone (CHH) gene is expressed in the hemocyte of Procambarus clarkii. In the present study, 2 additional cDNAs (CHH2-L and tCHH2) from the hemocyte and a CHH gene (CHH2) from the abdominal muscle of the same species were cloned. Analyses of the cDNA and genomic sequences suggested that, similar to other previously reported CHH genes, 2 precursor transcripts (CHH2 and CHH2-L) would be derived from CHH2 gene through a process of RNA alternative splicing, and CHH2 and CHH2-L each encode a precursor containing a signal peptide, a CHH precursor-related peptide, and a mature peptide. Further, tCHH2 sequence consists of exon I, exon II, and a truncated segment of intron II of CHH2 gene, followed by a previously unknown 3'sequence. It is suggested that, because the truncation disrupts the highly conserved RNA splice acceptor site, the truncated segment is retained within tCHH2, resulting in encoding a precursor containing the typical precursor components except the mature peptide is truncated with only 40 residues. In addition, unlike 2 other previously identified transcripts (referred to as CHH1 and CHH1-L), CHH2-L, CHH2, tCHH2 contain in the 3'-UTRs 3-5 AU-rich elements (AREs). The data showed that multiple CHH genes are expressed in crayfish hemocytes. Novel sequence characteristics of the transcripts result in an RNA splicing pattern that yields a transcript (tCHH2) encoding a precursor with an atypical truncated mature peptide and possibly leads to a different expression dynamics of the precursors encoded by the ARE-containing transcripts.