Novel tachykinins from the brain of the sea lamprey, Petromyzon marinus, and the skate, Raja rhina

Cloning and expression of tachykinins and their association with kisspeptins in the brains of zebrafish

The tachykinins are a family of neuropeptides, including substance P (SP), neurokinin A (NKA), and neurokinin B (NKB), that are encoded by the tac1 (SP and NKA) or tac2/3 (NKB) genes. Tachykinins are widely distributed in the central nervous system and have roles as neurotransmitters and/or neuromodulators. Recent studies in mammals have demonstrated the coexpression of NKB and kisspeptin and their comodulatory roles over the control of reproduction. We have recently identified two kisspeptin-encoding genes, kiss1 and kiss2, in teleosts. However, such relationship between tachykinins and kisspeptins has not been demonstrated in non-mammalian species. To determine the involvement of tachykinins in the reproduction in teleosts, we identified tac1 and two tac2 (tac2a and tac2b) sequences in the zebrafish genome using in silico data mining. Zebrafish tac1 encodes SP and NKA, whereas the tac2 sequences encode NKB and an additional peptide homologous to NKB (NKB-related peptide). Digoxigenin in situ hybridization in the brain of zebrafish showed tac1 mRNA-containing cells in the olfactory bulb, telencephalon, preoptic region, hypothalamus, mesencephalon, and rhombencephalon. The zebrafish tac2a mRNA-containing cells were observed in the preoptic region, habenula, and hypothalamus, whereas the tac2b mRNA-containing cells were predominantly observed in the dorsal telencephalic area. Furthermore, we examined the coexpression of tachykinins and two kisspeptin genes in the brain of zebrafish. Dual fluorescent in situ hybridization showed no coexpression of tachykinins mRNA with kisspeptins mRNA in hypothalamic nuclei or the habenula. These results suggest the presence of independent pathways for kisspeptins and NKB neurons in the brain of zebrafish.

Tachykinin peptides and receptors: putting amphibians into perspective

The tachykinins form one of the largest peptide families in nature. In this review, we describe the comparative features of the tachykinin peptides and their receptors, focusing particularly on amphibians. We also summarize our systematic studies of the localization, characteristics, and actions of bufokinin, a toad substance P-related peptide, in its species of origin. In addition, we discuss the establishment of multiple isoforms of the NK1-like receptor in the toad, and their structure, pharmacology and tissue distributions. We conclude that tachykinin peptides and receptors are well conserved in terms of their structures, physiological functions and coupling mechanisms during tetrapod evolution.

Immunohistochemical distribution of tachykinins in the CNS of the lamprey Petromyzon marinus

The presence of tachykinins in the CNS of vertebrates has been known for many decades, and numerous studies have described their distribution in mammals. Tachykinins were also reported in the CNS of lampreys using immunohistochemistry, chromatography, and radioimmunoassay methods, but the use of substance P (SP)-specific antibodies to reveal those tachykinins could have led to an underestimation of their number in this genus. Therefore, we carried out a new immunohistochemical study on Petromyzon marinus using a commercial polyclonal antibody that binds not only to mammalian SP, but also to other neurokinins. This antibody labeled all previously described lamprey tachykinin-containing neuronal populations, but more important, labeled new populations in several parts of the brain. These include the dorsal gray of the rostral spinal cord, the dorsal column nuclei, the octavolateral area, the nucleus of the solitary tract, the medial rhombencephalic reticular formation, the lateral tegmentum of the rostral rhombencephalon, the torus semicircularis, the optic tectum, the habenula, the mammillary area, the dorsal thalamic area, the lateral hypothalamus, and the septum area. Preabsorption experiments confirmed the binding of the antibody to neurokinins and allowed us to propose that the CNS of P. marinus contains at least two different tachykinins.

Tachykinin and Tachykinin Receptor of an Ascidian, Ciona intestinalis

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 gamma-preprotachykinin A (gamma-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.

Modulatory effect of substance P to the brain stem locomotor command in lampreys

Substance P initiates locomotion when injected in the brain stem of mammals. This study examined the possible role of this peptide on the supraspinal locomotor command system in lampreys. Substance P was bath applied or locally injected into an in vitro isolated brain stem, and the effects of the drug were examined on reticulospinal cells and on the occurrence of swimming in a semi-intact preparation. Bath applications of substance P induced sustained depolarizations occurring rhythmically in intracellularly recorded reticulospinal cells. Spiking activity was superimposed on the depolarizations and swimming was induced. The sustained depolarizations were abolished by tetrodotoxin, and substance P did not affect the membrane resistance of reticulospinal cells nor their firing properties, suggesting that it did not directly effect reticulospinal cells. To establish where the effects were exerted, successive lesions of the brain stem were made as well as local applications of the drug in the brain stem. Removing the mesencephalon abolished the sustained depolarizations, whereas large ejections of the drug in the mesencephalon excited reticulospinal cells and elicited bouts of swimming. More local injections into the mesencephalic locomotor region (MLR) also elicited swimming. After an injection of substance P, the current threshold needed to induce locomotion by MLR stimulation was decreased, and the size of the postsynaptic responses of reticulospinal cells to MLR stimulation was increased. Substance P also reduced the frequency of miniature spontaneous postsynaptic currents in reticulospinal cells. Taken together, these results suggest that substance P plays a neuromodulatory role on the brain stem locomotor networks of lampreys.

Evolution of vertebrate neuropeptides

This review describes some of the most typical features in the evolution of neuropeptides. Neuropeptides are synthesized like other polypeptides and proteins, with an amino acid sequence determined by the DNA sequence of the corresponding gene. Mutations of bases in the coding regions of the DNA lead to changes in amino acid sequence, and explain the differences in amino acid sequence of a certain neuropeptide in different animal species. The more distantly related two species are, the more substitutions can be found in one and the same neuropeptide. The biologically active part of the neuropeptide is usually the most conserved part. Neuropeptides also form families of closely related peptides, where several members may occur in one animal species. This is due to gene or exon duplications followed by mutations. Gene splicing and posttranslational processing decides the gene product in a single cell. Difference in sequence may cause difference in function, but more often than not, members of a family appear to produce the same effect. Three neuropeptide families, the tachykinins, the neuropeptide Y family, and the vasoactive intestinal polypeptide/pituitary adenylate cyclase-activating peptide family will be described in more detail.

Update: brain and pituitary hormones of lampreys

Lampreys and hagfish of the class Agnatha are of particular importance in understanding endocrinological relationships since they represent the oldest lineages of extant vertebrates which evolved over 550 million years ago. This review briefly summarizes the latest findings on the reproductive endocrinology of the sea lampreys. Since the First International Symposium of Fish Endocrinology in 1988, when virtually little was known of the hypothalamic-pituitary-gonadal axis, substantial new biochemical, molecular, physiological and immunological evidence has now clearly shown that lamprey reproduction is controlled by the neuroendocrine axis. In addition, five brain and six pituitary hormones of lampreys have been identified mainly by Sower and Kawauchi and colleagues between 1986 and 2000. We now hypothesize that lamprey reproduction is a highly synchronized process that is initiated or mediated by a coordination of complex integration of environmental cues and hormonal mechanisms which is broadly similar to that exhibited by gnathostome vertebrates.

Parallel bioassay of 39 tachykinins on 11 smooth muscle preparations. Structure and receptor selectivity/affinity relationship

Parallel bioassay on smooth muscle preparations demonstrated that: all TKs having a neutral or basic residue at position 7 from the C-terminus show a clear-cut preference for the NK1 TK receptor, reinforced by the presence of the aromatic doublet Phe-Phe or Phe-Tyr (aromatic TKs); all aliphatic TKs (Phe-Ile/Val) having an acidic residue at position 7 show a clear-cut preference for NK2/NK3 receptors, generally without selectivity for a single receptor. However, in aromatic TKs having the same acidic residue, the preference for NK2/NK3 receptors is weakened, with a more or less pronounced co-preference for the NK1 receptor. Amino acid substitutions in the C-terminal tripeptide may influence receptor affinity.

Tachykinins (substance P and neuropeptide gamma) from the brains of the pallid sturgeon, Scaphirhynchus albus and the paddlefish, Polyodon spathula (Acipenseriformes)

A peptide with substance P-like immunoreactivity was isolated from extracts of the brains of the pallid sturgeon, Scaphirhynchus albus and the North American paddlefish, Polyodon spathula. The primary structure of the peptide (Lys-Pro-Lys-Pro-His-Gln-Phe-Phe-Gly-Leu-Met.NH(2)) is the same in both species and contains 2 amino acid substitutions (Arg(1) --> Lys and Gln(5) --> His) compared with human substance P and 1 substitution (Arg(3) --> Lys) compared with substance P from the trout (Teleostei). Scyliorhinin I, a tachykinin previously isolated from an extract of sturgeon intestine, was not detected in either brain extract. A peptide with neurokinin A-like immunoreactivity (Ser-Ser-Ala-Asn-Arg-Gln-Ile-Thr-Gly-Lys(10)Arg-Gln-Lys-Ile-Asn-Ser-P he-Val-Gly-Leu(20)Met.NH(2)) was isolated from sturgeon brain and contains 10 amino acid substitutions compared with human neuropeptide gamma (a specific product of the posttranslational processing of gamma-preprotachykinin A) but only 4 substitutions compared with trout neuropeptide gamma. It was not possible to obtain the paddlefish neurokinin A-related peptide in pure form. The structural similarity between the sturgeon and the trout tachykinins supports the hypothesis that the Acipenseriformes (sturgeons and paddlefish) represent the sister group of the Neopterygii (gars, bowfin, and teleosts).

Purification and characterization of galanin and scyliorhinin I from the hybrid sturgeon, Scaphirhynchus platorynchus x Scaphirhynchus albus (Acipenseriformes)

The sturgeons (order Acipenseriformes) are extant representatives of a group of ancient Actinopterygian (ray-finned) fish. Galanin and scyliorhinin I (a tachykinin with limited structural similarity to mammalian substance P) have been isolated from an extract of the gastrointestinal tract of a sturgeon (an F1 hybrid between the shovelnose sturgeon, Scaphirhynchus platorynchus, and the pallid sturgeon, Scaphirhynchus albus). The primary structure of sturgeon galanin (Gly-Trp-Thr-Leu-Asn-Ser-Ala-Gly-Tyr-Leu10-Leu-Gly-Pro-His-Ala-Val -As p-Gly-His-Arg20-Ser-Leu-Ser-Asp-Lys-His-Gly-Leu-Pro.NH2) contains only two amino acid substitutions (Ser23 --> Asn and Pro29 --> Ala) compared with galanin from the bowfin, Amia calva (Amiiformes), but five amino acid substitutions compared with galanin from the trout (Teleostei). Similarly, the sturgeon tachykinin (Ser-Lys-Tyr-His-Gln-Phe-Tyr-Gly-Leu-Met.NH2) contains only one amino acid substitution (Tyr3 --> Ser) compared with scyliorhinin I previously isolated from bowfin stomach but five amino acid substitutions compared with trout substance P. The data support the hypothesis that the Acipenseriformes and the basal Neopterygians (gars and bowfin) share a close phylogenetic relationship.

Bufokinin: a substance P-related peptide from the gut of the toad, Bufo marinus with high binding affinity but low selectivity for mammalian tachykinin receptors

A tachykinin peptide, termed bufokinin, was isolated in pure form from an extract of the intestine of the toad, Bufo marinus, and its primary structure was established as: Lys-Pro-Arg-Pro-Asp-Gln-Phe-Tyr-Gly-Leu-Met.NH2. This sequence was confirmed by chemical synthesis and shows four amino acid substitutions (Arg1 --> Lys,Lys3 --> Arg,Gln5 --> Asp and Phe8 --> Tyr) compared with substance P. Binding parameters for synthetic bufokinin and mammalian tachykinins were compared using receptor-selective radioligands and crude membranes from rat tissues enriched in the NK-1 (submandibular gland) , NK-2 (stomach fundus) and NK-3 (brain) receptors. In terms of inhibiting the binding of the selective radioligands, bufokinin (Kd = 0.3 nM) was 1.8-fold more potent than substance P at the rat NK-1 site, but it was only 2-fold less potent (Kd = 2.8 nM) than neurokinin A at the NK-2 site and only 2-fold less potent (Kd = 48 nM) than neurokinin B at the NK-3 site. Thus, bufokinin shows relatively high affinity but lack of selectivity for all three tachykinin binding sites in rat tissues.

Neuropeptide families: evolutionary perspectives

Examination of neuropeptide families can provide information about phyletic relationships and evolutionary processes. In this article the oxytocin/vasopressin family, growth hormone releasing factor (GRF) superfamily and the substance P/tachykinin family have been considered in detail because they have been isolated from an extraordinarily diverse array of species from several vertebrate classes and invertebrate phyla. More important is that the nucleotide sequence of mRNA or cDNA encoding many of these peptides has been determined, which has allowed evolutionary distances to be estimated based on the DNA mutation rate. The origin of a given family lies in a primordial gene that arose many millions of years ago, and through time, exon duplication and insertion, gene duplication, point mutation and exon loss, the family developed into the forms that are now recognised. For example, in birds, GRF and pituitary adenylate cyclase activating peptide (PACAP) are encoded by the same gene, which probably arose as a result of exon duplication and tandem insertion of the ancestral GRF gene. In mammals GRF is the sole product on one gene, and PACAP is the product of a gene that also produces PACAP-related peptide (PRP), which is homologous to GRF. Thus it appears that between birds and mammals the GRF/PACAP gene duplicated: exon loss gave rise to the mammalian GRF gene, while mutation led to the formation of the mammalian PRP/PACAP gene. The neuropeptide Y superfamily is considered briefly, as is cionin, which is an invertebrate peptide that is closely related to the mammalian gastrin/cholecystokinin family.

Co-release of substance P and neurokinin A from the Atlantic cod stomach

The function of tachykinins in the control of gastric motility in the cod, Gadus morhua, was studied using native cod substance P ([Lys1, Arg3, Ile3]SP) and cod neurokinin A ([Ile3, Asn4]NKA). Both cod SP and NKA produced contractions of the vascularly perfused cod stomach, SP being almost 6 times more potent than NKA (pD2-values 7.05 +/- 0.06 and 6.28 +/- 0.09, respectively). The release of tachykinins from the cod stomach was measured in radioimmunoassay, using specific antibodies for the two cod tachykinins. Stimulation of the stomach motility by electrical stimulation of the vagus nerve or infusion of acetylcholine increased the amounts of SP and NKA released into the vascular perfusate. The results suggest that both tachykinins are involved in the excitatory response of the cod stomach produced by vagal and cholinergic stimulation.

Goldfish gamma-preprotachykinin mRNA encodes the neuropeptides substance P, carassin, and neurokinin A

Two cDNAs, size 969 bp and 1146 bp respectively, encoding goldfish gamma-preprotachykinin (gamma-PPT) were identified. Both cDNAs contain the same 345 bp open reading frame. The deduced 114-amino acid gamma-PPT contains the sequence of substance P, carassin and neurokinin A. sequence analysis of the two cDNA 5'-untranslated regions shows that the two cDNAs may represent different PPT-A gene transcripts resulting from the alternative transcriptional start sites. Expression of gamma-PPT mRNA was detected in a wide range of brain areas from the olfactory bulbs to the posterior brain region, as well as in the intestine, testis and pituitary.

Tachykinins with unusual structural features from a urodele, the amphiuma, an elasmobranch, the hammerhead shark, and an agnathan, the river lamprey

Tachykinins were purified from extracts of gastrointestinal tissues of the urodele, Amphiuma tridactylum (three-toed amphiuma), and the elasmobranch Sphyrna lewini (hammerhead shark), and from the brain of the agnathan Lampetra fluviatilis (river lamprey). The amphiuma substance P (SP) (DNPSVGQFYGLM-NH2) contains 12 amino residues compared with 11 for mammalian SP and lacks the Arg/Lys-Pro-Xaa-Pro motif that is characteristic of NK1 receptor-selective agonists. Lampetra SP (RKPHPKEFVGLM-NH2) is identical to SP from the sea lamprey and the shark SP-related peptide (AKFDKFYGLM-NH2) is identical to dogfish scyliorhinin I. Amphiuma neurokinin A (NKA) (HKDAFIGLM-NH2) and lamprey NKA (HFDEFVGLM-NH2) contain 9 amino acid residues compared with 10 for mammalian NKA. The shark NKA-related peptide (ASGPTQAGIV10GRKRQKGEMF20VGLM-NH2) shows limited structural similarity to mammalian neuropeptide gamma and the teleost tachykinin, carassin but contains 24 rather than 21 amino acid residues. The data show that the primary structures of the tachykinins have been very poorly conserved during vertebrate evolution and that pressure has acted only to maintain the functionally important sequence -Phe-Xaa-Gly Leu-Met-NH2 at the COOH-termini of the peptides.

Tachykinin-related neuropeptides in the central nervous system of the snail Helix pomatia: an immunocytochemical study

The distribution of neurons reacting with an antibody raised against an insect neuropeptide, locustatachykinin I, was investigated in the CNS of the snail Helix pomatia. The localization of the neurons was compared with that of the substance P-like immunoreactive (SPLI) neurons in the different ganglia. Altogether, there are approximately 800-1000 locustatachykinin-like immunoreactive (LomTKLI) neurons in the Helix CNS, occurring with an overwhelming dominancy (83.5%) in the cerebral ganglia. Within the cerebral ganglia, the majority of LomTKLI neurons were localized in the procerebrum. The number of SPLI neurons was high; approximately 2000 SPLI nerve cells were found in the Helix CNS. The majority (44.5%) of SPLI neurons was also found in the cerebral ganglia and they were also concentrated in the procerebrum. The neuropils of all ganglia were densely innervated by both LomTKLI and SPLI fibers except the medullary mass of the procerebrum where only SPLI elements form an extremely dense innervation. In addition to the neutrophil processes, LomTKLI neurons sent axon processes to the peripheral nerves. SPLI fibers also formed a dense network of varicose fibers in the connective tissue sheath around the ganglia where they innervated the blood vessel walls too. Immunolabeling on alternating cryostat sections revealed that LomTKLI and SPLI neurons are localized near each other in most cases; co-localization of the two immunoreactive materials could be seen in a very small number of neurons of the pedal and pleural ganglia. The present results show that the Helix CNS possesses distinct neuronal populations using different tachykinin-related peptides. It is suggested that the differential distribution of these neuropeptides also implies a diversity in their central and peripheral functions.