Tachykinin and Tachykinin Receptor of an Ascidian, Ciona intestinalis

Abstract

Tachykinins (TKs) are the most prevalent vertebrate brain/gut peptides. In this study, we originally identified authentic TKs and their receptor from a protochordate, Ciona intestinalis. The Ciona TK (Ci-TK) precursor, like mammalian ␥-preprotachykinin A (␥-PPTA), encodes two TKs, Ci-TK-I and -II, including the -FXGLM-NH 2 vertebrate TK consensus. Mass spectrometry of the neural extract revealed the production of both Ci-TKs. Ci-TK-I contains several Substance P (SP)-typical amino acids, whereas a Thr is exceptionally located at position 4 from the C terminus of Ci-TK-II. The Ci-TK gene encodes both Ci-TKs in the same exon, indicating no alternative generation of Ci-TKs, unlike the PPTA gene. These results suggested that the alternative splicing of the PPTA gene was established during evolution of vertebrates. The only Ci-TK receptor, Ci-TK-R, was equivalently activated by Ci-TK-I, SP, and neurokinin A at physiological concentrations, whereas Ci-TK-II showed 100-fold less potent activity, indicating that the ligand selectivity of Ci-TK-R is distinct from those of vertebrate TK receptors. Ci-TK-I, like SP, also elicited the typical contraction on the guinea pig ileum. The Ci-TK gene was expressed in neurons of the brain ganglion, small cells in the intestine, and the zone 7 in the endostyle, which corresponds to the vertebrate thyroid gland. Furthermore, the Ci-TK-R mRNA was distributed in these three tissues plus the gonad. These results showed that Ci-TKs play major roles in sexual behavior and feeding in protochordates as brain/gut peptides and endocrine/paracrine molecules. Taken together, our data revealed the biochemical and structural origins of vertebrate TKs and their receptors.

Molecular and functional characterization of cionin receptors in the ascidian, Ciona intestinalis: the evolutionary origin of the vertebrate cholecystokinin/gastrin family

“…Additionally, we observed the expression of ciors in the ovary, although neither biological action of CCK and gastrin nor the presence of CCK1R or CCK2R has ever been documented. Recently, we have substantiated that Ciona tachykinin, Ci-TK, induces vitellogenic oocyte growth via upregulation of gene expression of certain proteases (Satake et al 2004, Aoyama et al 2008, which is suppressed by a Ciona neurotensin-like peptide, Ci-NTLP6 . These studies, combined with the expression of cior genes in the ovary, raise the possibility that brain-gut peptides or nonsexual peptide hormones, including CCK/gastrin, are involved in novel reproductive functions.…”

Toll-like Receptors of the Ascidian Ciona intestinalis

“…RT-PCR-Total RNA (1 g) was reverse transcribed using oligo(dT) 20 primer, and PCR for Ci-TLR1, Ci-TLR2, and Ci-␤-actin (CLSTR00046) was performed using EX Taq polymerase (TaKaRa, Ohtsu, Japan). The PCR program was 94°C for 5 min and 35 cycles of 94°C for 1 min, 59°C for 1 min, and 72°C for 1 min.…”

Cross-kingdom hormonal signaling: an insight from thyroid hormone functions in marine larvae

“…Many authors homologize the endostyle of hemichordates, cephalochordates and urochordates with the thyroid gland of vertebrates using developmental molecular markers (TTF-1, TTF-2 and Pax-8, Mazet, 2002;Ogasawara et al, 1999b;Ogasawara and Satou, 2003;Ogasawara et al, 2001;Sasaki et al, 2003;Satake et al, 2004;Takacs et al, 2002;Valverde-R et al, 2004;Yu et al, 2002) and functional arguments (TPO, TG and TSH receptor, Ogasawara, 2000;Ogasawara et al, 1999a;Shepherdley et al, 2004;Valverde-R et al, 2004). However, both the endostyle and thyroid gland are present in such basal chordates as parasitic lampreys.…”