TISSUE-SPECIFIC ALTERNATIVE SPLICING OF TURKEY PREPROVASOACTIVE INTESTINAL PEPTIDE MESSENGER-RIBONUCLEIC-ACID, ITS REGULATION, AND CORRELATION WITH PROLACTIN SECRETION

Although vasoactive intestinal peptide (VIP) is a well characterized p hysiological PRL-releasing factor in avian species, its regulated expr ession is not fully understood. We cloned complementary DNAs encoding the prepro-turkey VIP (prepra-tVIP) molecule from an adult turkey hypo thalamic complementary DNA library. When the amino acid sequence of th e prepro-tVIP was compared to chicken and mammalian sequence, it was f ound that the isolated tVIP molecules lacked the 27-amino acid peptide histidine isoleucine (PHI) portion of the precursor protein. Several tissues showed an alternatively spliced tVIP transcript that lacked th e PHI sequence. Only in the hypothalamus did tVIP-specific primer pair s and reverse transcription-polymerase chain reaction produce two alte rnatively spliced fragments. The larger hypothalamus-specific fragment was subjected to nucleotide sequence analysis and identified as conta ining the alternatively spliced PHI-containing exon, which encoded a 2 7-amino acid PHI peptide in addition to the 8 amino acids that flanked the peptide. Hypothalamic tVIP expression was shown to be up-regulate d during the incubation phase of the reproductive cycle. The increased steady state level of tVIP messenger RNA appears to be regulated by n esting behavior, because nest deprivation dramatically suppressed its expression. Levels of the minor tVIP transcript containing both the PH I- and VIP-encoding exons did not significantly change between reprodu ctive stages and were maintained at approximately 4-6% of the total tV IP transcript level. Our findings provide further evidence that VIP is the most important PRL-releasing factor in birds. Our study should se rve as a useful model for determining whether PHI contributes in any w ay to the physiological role of PRL regulation. Revealing the tissue d istribution of VIP and PHI gene expression and tissue-specific alterna tive splicing could contribute to an understanding of the physiologica l functions of the two peptides as well as their relative roles in PRL regulation.