Tilapia glycoprotein hormone alpha subunit: cDNA cloning and hypothalamic regulation

The cDNA encoding the glycoprotein alpha (GP alpha) subunit of tilapia (Ore ochromis mossambicus) was partially cloned using RACE-polymerase chain reac tion (PCR) technique. The amplified cDNA was found to be 583 bases long, an d to consist of a portion of the signal peptide. the full sequence encoding the mature peptide (94 amino acids) and the 3' untranslated region. Northe rn blot analysis revealed a single band of approximately 600 bp. Alignment of the deduced amino acids of the mature protein showed that the tilapia GP alpha subunit shares more than 80% identity with that of other perciform f ish (i.e. striped bass. sea bream and yellowfin porgy) and less than 70% wi th that of more taxonomically remote fish and other vertebrates. Exposure o f dispersed tilapia pituitary cells to salmon gonadotropin-releasing hormon e (sGnRH) elevated GP alpha mRNA levels via both PKC and cAMP-protein kinas e A (PKA) pathways. The transcript levels were also regulated by pituitary adenylate cyclase activating polypeptide (PACAP) and neuropeptide Y (NPY), both acting through PKC and PKA pathways. Moreover, a combined treatment of PACAP or NPY with GnRH seems to have an additive effect on the GP alpha su bunit gene transcription. These results suggest that in tilapia the express ion of GP alpha subunit is regulated by GnRH mainly via PKC and PKA pathway s. Furthermore. PACAP and NPY can elevate the GnRH-stimulated GP alpha subu nit transcription and can directly affect the subunit mRNA levels. via the same transduction pathways. (C) 2001 Elsevier Science Ireland Ltd. All righ ts reserved.