Endocrine Abstracts

The tachykinin neurokinin B (NKB) has prominent roles in neuroendocrine function, behaviour and the control of reproductive processes, yet little is known about its evolution, potential splice variants or the manner in which it is processed. Indeed, the cloning of human TAC3 in 2000 revealed a single gene transcript encoding a single precursor and single tachykinin. Here, we deduce the phylogenetic relationship of a family of NKB peptides, and identify novel TAC3 splice variants and precursors. Phylogenetic analyses were performed following database mining; splice variants were identified following first strand cDNA synthesis and PCR using specific primers for TAC3 splice variants. Precursor analysis was performed by molecular size exclusion from brain and placental tissue and eluted fractions analyzed using NKB specific immunoassays. Database mining has revealed the existence of NKB peptides in 28 different species of mammals, birds and reptiles. PCR confirmed the existence of nine human splice variants of TAC3 (encoding a, b and gTAC3 precursors). gTAC3, albeit rarer, was found not to encode NKB. In rat brain (neuronal tissue) an NKB-like immunoreactivity peak was identified corresponding to the molecular size of the fully processed NKB peptide. In human placenta (endocrine tissue) the predominant NKB-like immunoreactivity was found in a significantly larger peak. The significance of the three different TAC3 precursors is not clear but could represent an evolutionary redundant splicing mechanism once employed by an ancestral gene that encoded two tachykinins. The larger peak of NKB-like immunoreactivity in placenta most likely represents an N-terminally extended NKB as the antibody was found to be selective for the C-terminally amidated peptide. The results indicate that differential RNA splicing and precursor processing is likely to play an important role in differentiating the actions of the TAC3 gene products in neuronal and endocrine tissues. Ethical approval was obtained for placentae.