Substance P-, neurotensin- and bombesin-like immunoreactivities in the gill epithelium of Ciona intestinalis L

Distribution and synaptic organization of substance P-like immunoreactive neurons in the mouse retina

Substance P (SP), a neuroprotective peptidergic neurotransmitter, is known to have immunoreactivity (IR) localized to amacrine and/or ganglion cells in a variety of species' retinas, but it has not yet been studied in the mouse retina. Thus, we investigated the distribution and synaptic organization of SP-IR by confocal and electron microscopy immunocytochemistry in the mouse retina. SP-IR was distributed in the inner nuclear layer (INL), inner plexiform layer (IPL), and ganglion cell layer (GCL). Most of the SP-IR somas belonged to amacrine cells (2.5% of all) in the INL and their processes stratified into the S1, S3, and S5 layers of the IPL, with the most intense band in the S5 layer. Some SP-IR somas can also be observed in the GCL, which were identified as displaced amacrine cells (82%, 1269/1550) and ganglion cells (18%, 281/1550) by antibodies against AP2α and RBPMS, respectively. Such SP-IR ganglion cells (1.2% of all RGCs) can be further divided into 3 subgroups expressing SP/α-Synuclein (α-Syn), SP/GAD67, and/or SP/GAD67/α-Syn. Possible physiological and pathological roles of these ganglion cells are discussed. Further, electron microscopy evidence demonstrates that SP-IR amacrine cells receive major inputs from other SP-IR amacrine cell processes (146/242 inputs) and output mostly to SP-negative amacrine cell processes (291/673 outputs), suggesting series inhibition among amacrine cells. These results reveal for the first time an explicit distribution, novel ganglion cell features, and synaptic organization of SP-IR in the mouse retina, which is important for the future use of mouse models to study the roles of SP in healthy and diseased (including Parkinson's disease) retinal states.

Insulin-like genes in ascidians: findings in Ciona and hypotheses on the evolutionary origins of the pancreas

Insulin plays an extensively characterized role in the control of sugar metabolism, growth and homeostasis in a wide range of organisms. In vertebrate chordates, insulin is mainly produced by the beta cells of the endocrine pancreas, while in non-chordate animals insulin-producing cells are mainly found in the nervous system and/or scattered along the digestive tract. However, recent studies have indicated the notochord, the defining feature of the chordate phylum, as an additional site of expression of insulin-like peptides. Here we show that two of the three insulin-like genes identified in Ciona intestinalis, an invertebrate chordate with a dual life cycle, are first expressed in the developing notochord during embryogenesis and transition to distinct areas of the adult digestive tract after metamorphosis. In addition, we present data suggesting that the transcription factor Ciona Brachyury is involved in the control of notochord expression of at least one of these genes, Ciona insulin-like 2. Finally, we review the information currently available on insulin-producing cells in ascidians and on pancreas-related transcription factors that might control their expression.

Endocrinology of protochordates

Large-scale gene duplications occurred early in the vertebrate lineage after the split with protochordates. Thus, protochordate hormones and their receptors, transcription factors, and signaling pathways may be the foundation for the endocrine system in vertebrates. A number of hormones have been identified including cionin, a likely ancestor of cholecytokinin (CCK) and gastrin. Both insulin and insulin-like growth hormone (IGF) have been identified in separate cDNAs in a tunicate, whereas only a single insulin-like peptide was found in amphioxus. In tunicates, nine distinct forms of gonadotropin-releasing hormone (GnRH) are shown to induce gamete release, even though a pituitary gland and sex steroids are lacking. In both tunicates and amphioxus, there is evidence of some components of a thyroid system, but the lack of a sequenced genome for amphioxus has slowed progress in the structural identification of its hormones. Immunocytochemistry has been used to tentatively identify a number of hormones in protochordates, but structural and functional studies are needed. For receptors, protochordates have many vertebrate homologs of nuclear receptors, such as the thyroid, retinoic acid, and retinoid X receptors. Also, tunicates have cell surface receptors including the G-protein-coupled type, such as β-adrenergic, putative endocannabinoid, cionin (CCK-like), and two GnRH receptors. Several tyrosine kinase receptors include two epidermal growth factor (EGF) receptors (tunicates) and an insulin/IGF receptor (amphioxus). Interestingly, neither steroid receptors nor a full complement of enzymes for synthesis of sex steroids are encoded in the Ciona genome. Tunicates appear to have some but not all of the necessary molecules to develop a vertebrate-like pituitary or complete thyroid system.

Molecular cloning and expression of cDNA encoding a brain bombesin/gastrin-releasing peptide-like peptide in goldfish

A complementary DNA (cDNA) of 928 bp encoding a bombesin (BBS)/gastrin-releasing peptide (GRP) precursor was identified from goldfish brain. Goldfish BBS/GRP messenger RNA (mRNA) encodes a 157 amino acid precursor, which contains a signal peptide sequence, the 22 amino acid putative BBS/GRP-like peptide, and a carboxy-terminal extension peptide. Reverse transcription-polymerase chain reaction (PCR) (RT-PCR) demonstrated that the mRNA for this precursor has a widespread distribution in goldfish brain, and is also present in skin, gastrointestinal tract, gonad, and gill. Phylogenetic analysis of BBS/GRP-like peptide precursors in vertebrates shows that goldfish BBS/GRP is more closely related to the known GRP precursors than to BBS precursors.

Pulmonary Neuroendocrine Cells and Lung Development

Pulmonary neuroendocrine cells produce bioactive peptides such as gastrin-releasing peptide (GRP) at high levels in developing fetal lung. The role of GRP and other peptides in promoting branching morphogenesis, cell proliferation, and cell differentiation during lung organogenesis is reviewed. Possible roles for bioactive peptides derived from these cells in the pathophysiology of perinatal lung disorders are discussed.

Localization of immunoreactive gastrin-like cells in the alimentary tract of the ascidian Styela plicata

The occurrence of a gastrin-like immunoreactivity in the alimentary tract of the ascidian Styela plicata has been investigated using immunocytochemical methods. Gastrin-like cells are present only in the gastric epithelium among the cell types responsible for digestion and absorption of food. The physiological role played by the ascidian gastrin-like peptides is discussed together with the evolutionary history of peptides of the gastrin/cholecystokinin family.

Tachykinins in the central and peripheral nervous system of the ascidian Ciona intestinalis

Immunochemical studies were carried out on the ascidian Ciona intestinalis to determine the character and distribution of the tachykinins neurokinin A (NKA) and substance P (SP). Antisera specific for the C-terminus of mammalian SP, and for the N-terminus of mammalian SP and NKA, were used to monitor tissue extracts from Ciona. Parallel immunocytochemical studies assessed the distribution of these tachykinins in the central and peripheral nervous systems as well as their occurrence in endocrine cells. HPLC and radioimmunoassay established the presence of both C-terminal SP and NKA-like material in extracts from neural ganglion and body wall/pharynx. Immunocytochemistry revealed the C-SP material to be present in a population of small neuronal cell bodies and fibers in the ganglion as well as in cell bodies and fibers in the periphery. The NKA-like material was restricted to separate and larger neuronal perikarya in the ganglion while in the periphery its distribution reflected that of the C-SP-like material. Endocrine cells in the pharyngeal epithelium were reactive only with the C-terminal SP antiserum. N-terminal SP antisera were unreactive both in radioimmunoassay and immunocytochemistry. These findings are in accord with the idea that the tachykinin family is represented by at least two of its members at the prevertebrate stage of evolution. Interestingly, the SP-like material shows strong C-terminal homology with the mammalian peptide but little N-terminal similarity. Furthermore, the NKA-like peptide is restricted to the nervous system while SP-like molecules may be found in both central and peripheral neurons as well as endocrine cells in the pharynx.

Neurotensin-like immunoreactivity in the pituitary and hypothalamus of bony fishes

Using an antiserum raised against synthetic neurotensin (NT), the distribution of immunoreactivity in the pituitary and hypothalamus has been examined by immunocytochemistry at light and electron microscope level in a number of species of bony fishes. In most species immunoreactive perikarya were found in the preoptic region of the hypothalamus, with fibres throughout the tuberal hypothalamus and neurohypophysis (neural lobe and median eminence). In the neurohypophysis of teleosts NT-like immunoreactivity was seen in a dense band of fibres bordering the ACTH cells of the rostral pars distalis: absorption controls showed that this was due to the presence of an NT(8-13)-like or xenopsin-like sequence, which, according to electron microscopic observations, was contained in small dense cored vesicles. The antiserum also stained the pituitary ACTH cells of some species, apparently due to cross-reaction with the 17-19 sequence of ACTH. These results suggest that an NT-like peptide may have a role in control of the adenohypophysis in fishes.

Active peptides from amphibian skin are also amphibian neuropeptides

Immunohistochemical data on several newt brain areas showed a heterogeneous system of neuronal elements, immunopositive for antisera specifically directed to different antigenic determinants of tachykinin molecules. Acid extracts of newt brain areas were immunopositive for substance P with an antibody specific for the COOH-terminal (tachykinin determinant) and exhibits an elution profile by gel filtration characteristic to substance P. Bombesin-like immunoreactivity was demonstrable both by immunohistochemistry (fibers and cell bodies in forebrain and hypothalamic areas) and by radioimmunoassay, using an antiserum specific for the mid-region of the molecule. This immunoreactivity was separated into two peaks by gel filtration chromatography. Sauvagine-like material was detected by immunohistochemistry in newt hypothalamus as a loose preoptic cell system and as a thin fiber layer in the outer zone of the median eminence. Double staining procedures demonstrate that sauvagine and CRF are spatially closely related but separable in both the preoptic area and in the median eminence. This data on the presence of several amphibian skin peptides in the CNS of the newt suggests their possible role as neuropeptide.

CCK-like peptides in the neural complex of a protochordate

The neural complex of the ascidian Styela plicata has been investigated by means of cytochemical and immunocytochemical methods. In the cerebral ganglion, using a mammalian antibody to synthetic CCK-8, immunoreactive neurons and nerve fibers have been localized; at the same time immunofluorescent cells are scattered in some glandular lobules of the neural gland. The possible functions of a CCK-8-like peptide in ascidians is suggested and discussed.

Gastro-intestinal and neurohormonal peptides in the alimentary tract and cerebral complex of Ciona intestinalis (Ascidiaceae)

Polypeptide-hormone producing cells were localized in the alimentary tract and cerebral ganglion of Ciona intestinalis using cytochemical, immunocytochemical and electron-microscopical methods. Antisera to the following peptides of vertebrate type were employed: bombesin, human prolactin (hPRL), bovine pancreatic polypeptide (PP), porcine secretin, motilin, vasoactive intestinal polypeptide (VIP), beta-endorphin, leu-enkephalin, met-enkephalin, neurotensin, 5-hydroxytryptamin (5-HT), cholecystokinin (CCK), human growth (GH), ACTH, corticotropin-like intermediate lobe peptide (CLIP) and gastric inhibitory peptide (GIP). Immunoreactive cells were found both in the alimentary tract epithelium and in the cerebral ganglion for bombesin, PP, substance P, somatostatin, secretin and neurotensin. Additionally, in the cerebral ganglion only, there were cells immunoreactive for beta-endorphin, VIP, motilin and human prolactin. 5-HT positive cells, however, were restricted to the alimentary tract. No immunoreactivity was obtained either in the cerebral ganglion or in the alimentary tract with antibodies to leu-enkephalin, met-enkephalin, CCK, growth hormone, ACTH, CLIP and GIP. Prolactin-immunoreactive and pancreatic polypeptide-immunoreactive cells were argyrophilic with the Grimelius' stain and were found in neighbouring positions in the cerebral ganglion. At the ultrastructural level five differently granulated cell types were distinguished in the cerebral ganglion. Granules were present in the perikarya as well as in axons. The possible functions of the peptides as neurohormones, neuroregulators and neuromodulators are discussed.

Neurotensin-like immunoreactivity in the nervous system of hydra

Neurotensin-like immunoreactivity is found in nerve fibers present in all body regions of hydra. The nerve fibers are especially numerous in the ectoderm at the bases of the tentacles and in the ectoderm at a site just above the foot. Radioimmunoassays of acetic-acid extracts of hydra, using various region-specific antisera towards mammalian neurotensin, show the presence of multiple neurotensin-related peptides. The amounts of these peptides vary between 1 and 350 pmol per gram wet weight. Gel filtration on Sephadex G-25 reveals a fraction of neurotensin-like peptides that crossreact equally well with an antiserum directed against sequence 1-8 and an antiserum directed against sequence 6-13 of neurotensin. This fraction elutes also at the position of neurotensin and might closely resemble the mammalian peptide. A fraction eluting with the void volume crossreacts preferentially with antisera directed against sequences 1-8 and 10-13 of neurotensin. Several components of apparent lower molecular weight than neurotensin crossreact preferentially with an antiserum against sequence 10-13. These last peptides represent the major portion of the neurotensin-like peptides in hydra.

Bombesin-like immunoreactivity in the nervous system of hydra

With immunocytochemical methods, nerve cells have been detected in Hydra attenuata containing bombesin-like immunoreactivity. These nerve cells are located in ectoderm of all body regions of the animal and are especially abundant in basal disk and tentacles. Radioimmunoassay of extracts of hydra demonstrated at least 0.2 pmol/g wet weight of bombesin-like immunoreactivity. The immunoreactive material elutes from Sephadex G-50 in a similar position to synthetic bombesin. The data show that bombesin-like peptides are among the phylogenetically oldest neuropeptides found so far.