TAC3 is a member of tachykinins and its gene product neurokinin B (NKB) has recently emerged as a key regulator for luteinizing hormone (LH) through modulation of kisspeptin/GnRH system within the hypothalamus. In fish models, TAC3 not only encodes NKB but also a novel tachykinin-like peptide called NKB-related peptide (NKBRP) and the pituitary actions of these TAC3 gene products are still unknown. Using grass carp as a model, the direct effects and post-receptor signaling for the two TAC3 products were examined at the pituitary level. Grass carp TAC3 was cloned and confirmed to encode NKB and NKBRP similar to that of other fish species. In carp pituitary cells, NKB and NKBRP treatment did not affect LH release... More
TAC3 is a member of tachykinins and its gene product neurokinin B (NKB) has recently emerged as a key regulator for luteinizing hormone (LH) through modulation of kisspeptin/GnRH system within the hypothalamus. In fish models, TAC3 not only encodes NKB but also a novel tachykinin-like peptide called NKB-related peptide (NKBRP) and the pituitary actions of these TAC3 gene products are still unknown. Using grass carp as a model, the direct effects and post-receptor signaling for the two TAC3 products were examined at the pituitary level. Grass carp TAC3 was cloned and confirmed to encode NKB and NKBRP similar to that of other fish species. In carp pituitary cells, NKB and NKBRP treatment did not affect LH release and gene expression but up-regulated prolactin (PRL) and somatolactin α (SLα) secretion, protein production and transcript expression. The stimulation by these two TAC3 gene products on PRL and SLα release and mRNA levels were mediated by pituitary NK2 and NK3 receptors, respectively. Apparently, NKB- and NKBRP-induced SLα secretion and transcript expression were caused by AC/cAMP/PKA, PLC/IP3/PKC and Ca2+/CaM/CaMK-II activation. The signal transduction for the corresponding responses on PRL release and mRNA expression were also similar, except that the PKC component was not involved. These findings suggest that the two TAC3 gene products do not play a role in LH regulation at the pituitary level in carp species but may serve as novel stimulators for PRL and SLα synthesis and secretion via overlapping post-receptor signaling mechanisms coupled to NK2 and NK3 receptors, respectively.
