Differential splicing of the growth hormone-releasing hormone gene in rat placenta generates a novel pre-proGHRH mRNA that encodes a different C-terminal flanking peptide.

We have isolated and characterized a novel rat placental pre-proGHRH mRNA (pre-proGHRH-2 mRNA). This mRNA is generated by an alternative splicing process which results in the presence of an additional exon of 156 bp (designated exon 4.5) located between exons 4 and 5 of the previously reported hypothalamic and placental pre-proGHRH mRNA (pre-proGHRH-1 mRNA). Since the sequences encoding mature GHRH are included within exons 3 and 4, the processing of pre-proGHRH-2 would not affect the synthesis of mature GHRH but would generate a C-terminal peptide (designated GCTP-2) different from that previously reported in the hypothalamus and placenta (GCTP-1). The putative GCTP-2 has 64 amino acids, and the first 18 N-terminal residues are identical to those present in GCTP-1 (30 amino acids long). Pre-proGHRH-2 mRNA has not been detected in the hypothalamus.