Eel tachykinin-3 : characterization, pituitary role and evolutionary perspective. Aurora Campo, Anne-Gaëlle Lafont, Benjamin Lefranc, Jérôme Leprince, Hervé Tostivint, Nédia Kamech, Sylvie Dufour and Karine Rousseau. 2018. Frontiers in Endocrinology 9:304. doi: 10.3389/fendo.2018.00304
The European eel (Anguilla anguilla) is a non-conventional model of interest due to its basal phylogenetical position in teleosts and its particular biological cycle with a blockade at pre-puberty until the oceanic reproductive migration does not occur. In the frame of Aurora Campo’s PhD, we investigated, in this species, the role of neurokinin B (NKB), peptide encoded by tac3 gene, which is involved in mammals in the cerebral control of reproduction by activating the neurons of gonadotropin-releasing hormone (GnRH) which stimulates pituitary gonadotropins, LH (luteinising hormone) and FSH (follicle-stimulating hormone). This study was done in the frame of European IMPRESS (Improved Production Strategies for Endangered Freshwater Species) ITN and NEMO (Neuropeptides in Marine Organisms) ANR. We identified two paralogous genes in the eel genome, tac3a and tac3b, each encoding two peptides (NKBa and NKP-RPa for tac3a; NKBb and NKB-RPb for tac3b). The sequence of eel NKBa is identical to that of human NKB, showing a strong conservation among vertebrates. The sequences of the three other peptides are new sequences. These four peptides possess a similar alpha helix 3D structure. By means of phylogeny and synteny analyses, we determined that tac3a and tac3b genes likely resulted from the teleost-specific whole duplication. Among teleosts, TAC3b sequences are more divergent than TAC3a, and tac3b gene would have been lost in some teleost lineages. We cloned and sequenced tac3a and tac3b cDNAs from the eel brain, and the tissue distributions of both transcripts, as investigated by qPCR, showed that they are primarily expressed in the diencephalon. The predicted four eel peptides were synthesized. Using primary culture of eel pituitary cells, we showed that all four peptides were able to specifically and dose-dependently inhibited lhb expression (without any effect on fshb), as well as the expression of type 2 GnRH receptor (gnrh-r2). Our findings reveal that the peptides encoded by the two tac3 genes could contribute to the strong blockade of puberty in the European eel, via a double direct inhibitory control at the pituitary level on LH and GnRH receptor. Thus, despite a strong sequence conservation, NKB peptides show a functional plasticity with opposite roles in the control of reproduction among vertebrates.