Molecular cloning and gonadotropin-releasing hormone regulation of receptor activated for C protein kinase (RACK) in tilapia Oreochromis mossambicus

Abstract

A receptor for activated C-kinase (RACK) cDNA in the Mozambique tilapia (Oreochromis mossambicus) was cloned by reverse transcriptase polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE), and it was compared with other vertebrates. Nucleotide sequence analysis revealed that the full length of cDNA (1109 bp) cloned encompasses 954 bp open reading frame encoding 317 amino acid residues. The deduced amino acid sequence shares 95–99% identity with the teleosts and 77–95% compared with other vertebrates. Like most RACK sequences in other vertebrates, seven repeats of the WD-40 motif are well-conserved in the sequence of the tilapia. Further, the effectiveness of gonadotropin-releasing hormone (GnRH) regulation of RACK LH, and FSH gene expression was further investigated by a single injection of salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II). The results showed that injection of tilapia brain with either sGnRH or cGnRH-II significantly increased mRNA levels of RACK, which then stimulate LH and FSH. This result suggests that RACK and protein kinase C (PKC) are involved in GnRH-mediated gonadotropin hormone (GtH) release. In addition, cGnRH-II enhanced the FSH and LH mRNA as well as sGnRH expression levels in tilapia; these results further demonstrate that both sGnRH and cGnRH regulate GtH through PKC.