Characterization of melanin concentrating hormone in teleost hypothalamus

The evolution of neuropeptide signalling: insights from echinoderms

Neuropeptides are evolutionarily ancient mediators of neuronal signalling that regulate a wide range of physiological processes and behaviours in animals. Neuropeptide signalling has been investigated extensively in vertebrates and protostomian invertebrates, which include the ecdysozoans Drosophila melanogaster (Phylum Arthropoda) and Caenorhabditis elegans (Phylum Nematoda). However, until recently, an understanding of evolutionary relationships between neuropeptide signalling systems in vertebrates and protostomes has been impaired by a lack of genome/transcriptome sequence data from non-ecdysozoan invertebrates. The echinoderms—a deuterostomian phylum that includes sea urchins, sea cucumbers and starfish—have been particularly important in providing new insights into neuropeptide evolution. Sequencing of the genome of the sea urchin Strongylocentrotus purpuratus (Class Echinoidea) enabled discovery of (i) the first invertebrate thyrotropin-releasing hormone-type precursor, (ii) the first deuterostomian pedal peptide/orcokinin-type precursors and (iii) NG peptides—the ‘missing link’ between neuropeptide S in tetrapod vertebrates and crustacean cardioactive peptide in protostomes. More recently, sequencing of the neural transcriptome of the starfish Asterias rubens (Class Asteroidea) enabled identification of 40 neuropeptide precursors, including the first kisspeptin and melanin-concentrating hormone-type precursors to be identified outside of the chordates. Furthermore, the characterization of a corazonin-type neuropeptide signalling system in A. rubens has provided important new insights into the evolution of gonadotropin-releasing hormone-related neuropeptides. Looking forward, the discovery of multiple neuropeptide signalling systems in echinoderms provides opportunities to investigate how these systems are used to regulate physiological and behavioural processes in the unique context of a decentralized, pentaradial bauplan.

Transcriptomic identification of starfish neuropeptide precursors yields new insights into neuropeptide evolution

Neuropeptides are evolutionarily ancient mediators of neuronal signalling in nervous systems. With recent advances in genomics/transcriptomics, an increasingly wide range of species has become accessible for molecular analysis. The deuterostomian invertebrates are of particular interest in this regard because they occupy an ‘intermediate' position in animal phylogeny, bridging the gap between the well-studied model protostomian invertebrates (e.g. Drosophila melanogaster, Caenorhabditis elegans) and the vertebrates. Here we have identified 40 neuropeptide precursors in the starfish Asterias rubens, a deuterostomian invertebrate from the phylum Echinodermata. Importantly, these include kisspeptin-type and melanin-concentrating hormone-type precursors, which are the first to be discovered in a non-chordate species. Starfish tachykinin-type, somatostatin-type, pigment-dispersing factor-type and corticotropin-releasing hormone-type precursors are the first to be discovered in the echinoderm/ambulacrarian clade of the animal kingdom. Other precursors identified include vasopressin/oxytocin-type, gonadotropin-releasing hormone-type, thyrotropin-releasing hormone-type, calcitonin-type, cholecystokinin/gastrin-type, orexin-type, luqin-type, pedal peptide/orcokinin-type, glycoprotein hormone-type, bursicon-type, relaxin-type and insulin-like growth factor-type precursors. This is the most comprehensive identification of neuropeptide precursor proteins in an echinoderm to date, yielding new insights into the evolution of neuropeptide signalling systems. Furthermore, these data provide a basis for experimental analysis of neuropeptide function in the unique context of the decentralized, pentaradial echinoderm bauplan.

Regulation of food intake by melanin-concentrating hormone in goldfish

Melanin-concentrating hormone (MCH), originally discovered in the teleost pituitary, is a hypothalamic neuropeptide involved in the regulation of body color in fish. Although MCH is also present in the mammalian brain, it has no evident function in providing pigmentation. Instead, this peptide is now recognized to be one of the key neuropeptides that act as appetite enhancers in mammals such as rodents and primates. Although there has been little information about the central action of MCH on appetite in fish, recent studies have indicated that, in goldfish, MCH acts as an anorexigenic neuropeptide, modulating the alpha-melanocyte-stimulating hormone signaling pathway through neuronal interaction. These observations indicate that there may be major differences in the mode of action of MCH between fish and mammals. This paper reviews what is currently known about the regulation of food intake by MCH in fish, especially the goldfish.

Effects of tank color on melanin-concentrating hormone levels in the brain, pituitary gland, and plasma of the barfin flounder as revealed by a newly developed time-resolved fluoroimmunoassay

A pleuronectiform fish, the barfin flounder Verasper moseri, reared in a white tank had a smaller ratio of pigmented area of the skin on non-eyed side, grew faster, and had greater melanin-concentrating hormone (MCH)-immunoreactive cell bodies and MCH gene expression in the brain than in the black tank, indicating that synthesis and release of MCH are higher in fish from a white tank. In the present study, a time-resolved fluoroimmunoassay for MCH was developed. MCH levels were assessed in the brain, pituitary gland, and plasma of barfin flounders reared in a white or black tank. A competitive assay using two antibodies was performed among secondary antibodies in the solid phase, MCH antibodies, samples, and europium-labeled MCH. Displacement curves of serially diluted extracts (brain, pituitary gland, and plasma) of the barfin flounder paralleled that of the MCH standard. MCH levels in the brain and plasma were higher in fish reared in the white tank for 5 months than in the black tank. These results suggest that synthesis and secretion of MCH are enhanced with the white background and that MCH is involved in both somatic growth and the skin pigmentation in the barfin flounder.

The hypothalamo-hypophyseal system of the white seabream Diplodus sargus: immunocytochemical identification of arginine-vasotocin, isotocin, melanin-concentrating hormone and corticotropin-releasing factor

The distribution of the neurosecretory hormones vasotocin, isotocin and melanin-concentrating hormone and the hypophysiotropic hormone corticotropin-releasing factor was studied in the hypothalamo-hypophyseal system of the white seabream (Diplodus sargus) using immunocytochemical techniques. Magnocellular and parvocellular perikarya immunoreactive for arginine-vasotocin and isotocin were present in the nucleus preopticus. Perikarya immunoreactive for arginine-vasotocin extended more caudally with respect to isotocin-immunoreactive perikarya. Parvocellular perikarya were located at rostroventral levels and magnocellular perikarya in the dorsocaudal portion of the nucleus. Arginine-vasotocin and isotocin did not coexist in the same neuron. Fibres immunoreactive for arginine-vasotocin and isotocin innervated all areas of neurohypophysis and terminate close to corticotropic and melanotropic cells. Perikarya immunoreactive for melanin-concentrating hormone and corticotropin-releasing factor were observed in the nucleus lateralis tuberis, with a few neurons in the nucleus periventricularis posterior. In addition, melanin-concentrating hormone immunoreactive perikarya were detected in the nucleus recessus lateralis. The preoptic nucleus did not show immunoreactivity for these antisera. Fibres showing melanin-concentrating hormone and corticotropin-releasing factor immunoreactivity ended close to the melanotropic and somatolactotrophic cells of the pars intermedia, and close to the corticotrophic cells of the rostral pars distalis.

Melanotropic peptides in the mammalian brain: the melanin-concentrating hormone

Melanin-concentrating hormone (MCH) has been identified in neurons of the mammalian brain. This review summarizes some current information regarding the cell biology of this neuropeptide and the topography of MCH-immunoreactive (-IR) neurons in several species including mouse, rat, hamster, guinea pig, rabbit, dog and monkey; and atlas of MCH-IR neurons in the hypothalamus and subthalamus of the brain of guinea pig is presented. Based upon the location of this MCH cell group, it is hypothesized that they may be functionally involved in circuits of extrapyramidal motor systems from striatal centers to the thalamus and cerebral cortex and to the midbrain and spinal cord.

Development of melanin-concentrating hormone-immunoreactive elements in the brain of gilthead seabream (Sparus auratus)

The development of the hypothalamic melanin-concentrating hormone (MCH) system of the teleost Sparus auratus has been studied by immunocytochemistry using an anti-salmon MCH serum. Immunoreactive perikarya and fibers are found in embryos, larvae, and juvenile specimens. In juveniles, most labeled neurons are present in the nucleus lateralis tuberis; some are dispersed in the nucleus recessus lateralis and nucleus periventricularis posterior. From the nucleus lateralis tuberis, MCH neurons project a conspicuous tract of fibers to the ventral hypothalamus; this penetrates the pituitary stalk and reaches the neurohypophysis. Most fibers end close to the cells of the pars intermedia, and some reach the adenohypophysial rostral pars distalis. Immunoreactive fibers can also be seen in extrahypophysial localizations, such as the preoptic region and the nucleus sacci vasculosi. In embryos, MCH-immunoreactive neurons first appear at 36h post-fertilization in the ventrolateral margin of the developing hypothalamus. In larvae, at 4 days post-hatching, perikarya can be observed in the ventrolateral border of the hypothalamus and in the mid-hypothalamus, near the ventricle. At 26 days post-hatching, MCH perikarya are restricted to the nucleus lateralis tuberis. The neurohypophysis possesses MCH-immunoreactive fibers from the second day post-hatching. The results indicate that MCH plays a role in larval development with respect to skin melanophores and cells that secrete melanocyte-stimulating hormone.

The biosynthesis of melanin-concentrating hormone in a fish

Abstract This work investigated the biosynthesis of a neurohypophysial hormone, melanin-concentrating hormone (MCH), in the trout. Sephadex G-75 chromatography showed the presence of several large MCH-immunoreactive molecules in hypothalamic and pituitary gland extracts, with different retention times on high-performance liquid chromatography from the mature MCH(1-17). About 10% of the total MCH-immunoreactivity in the hypothalamus was attributable to large molecular weight forms but these contributed less than 1% to the immunoreactivity in the neurointermediate lobe. Both [(35) S]methionine and [(3) H]leucine were injected into the hypothalamus near the MCH perikarya (nucleus lateralis tuberis region) of anaesthetized fish, after which the fish were killed at intervals of up to 8 h post-injection and the basal hypothalami, pituitary pars distales and neurointermediate lobes were extracted in acid. MCH-related immunoprecipitates from these extracts were fractionated by sodium dodecyl sulphate polyacrylamide gel electrophoresis or by Sephadex G-50 chromatography. The results show the incorporation of radiolabel into 15.3 K and 11.3 K precursors within 0.75 h, and their conversion, via several smaller intermediates, to a molecule resembling MCH(1-17). The results are discussed in relation to the known cDNA sequence of salmon MCH. Labelled MCH first appeared in the neurointermediate lobe 4 h after injection, giving an estimated transit rate of 0.4 mm/h.

Structures of two genes coding for melanin-concentrating hormone of chum salmon

Two MCH genes coding for melanin-concentrating hormone (MCH) were isolated from a chum salmon liver DNA library and characterized. They were shown to be intronless genes with 0.63-kb exons, each of which commonly consisted of an about 80-bp 5'-untranslated region, a region coding for 132 amino acids (aa) MCH precursor protein and an approx. 160-bp 3'-untranslated region. About 20 bp upstream from the putative cap site, sequences were found corresponding to the TATA box. The two genes were 86% identical at the nucleotide sequence level. Sequences homologous to the chum salmon MCH genes were present in the genomes of other fish such as catfish, carp and Chinese grass carp, whereas no highly homologous sequence could be detected in other vertebrate genomes.

Two precursors of melanin-concentrating hormone: DNA sequence analysis and in situ immunochemical localization

Two precursors to Chinook salmon (Oncorhynchus tshawytscha) melanin-concentrating hormone, an important factor in teleosts involved in the control of skin pigmentation and stress responsiveness, have been identified from DNA sequence analysis. Both precursors encode proteins of 132 amino acids and they share 107/132 amino acid identities. The biologically active 17-residue peptide is located at the C terminus of both precursors and can be liberated by proteolytic cleavage following two adjacent arginine residues. Additional putative proteolytic processing sites are located within the two precursors. Northern analysis demonstrated an intense hybridization signal of 750 nucleotides in the hypothalamus. Immunocytochemical studies as well as in situ hybridization analyses identify intensely staining cell bodies in the hypothalamus in the area of the lateral tuberal nucleus.

Melanin concentrating hormone. II. Structure and biosynthesis of melanin-concentrating hormone

Melanin-concentrating hormone is a neuropeptide produced in teleost hypothalami and transferred to the neurohypophysis. Salmon MCH was a novel cyclic heptadecapeptide capable of inducing melanin aggregation of integumentary melanophores at picoto nano-molar concentrations in all teleosts tested. The MCH gene is intronless and the exon encodes a 132 amino acid precursor protein, in which the heptadecapeptide of MCH locates at the C-terminal end. Immunohistochemical surveys with anti-salmon MCH antiserum strongly suggest that an MCH-like peptide is present in the hypothalami of higher vertebrates. Biological effects of salmon MCH on other vertebrates are found to be versatile.

Structures of two kinds of mRNA encoding the chum salmon melanin-concentrating hormone

The structures of two kinds of melanin-concentrating hormone (MCH) cDNA clones isolated from a chum salmon hypothalamus cDNA library were described. The MCH heptadecapeptide was present at the C terminus of a putative MCH precursor consisting of 132 amino acid residues. The two clones were 80% homologous with each other at the amino acid sequence level. Two genes, each directing one of the mRNAs was noted at about a single copy per haploid salmon genome. MCH genes were efficiently expressed as 0.9-kb poly(A)+RNA in salmon hypothalamus, and sequences hybridizable with salmon MCH cDNA were found in rat hypothalamus.

Melanin-concentrating hormone-like immunoreactive material in the rat hypothalamus; characterization and subcellular localization

Melanin-concentrating hormone (MCH) is a neurosecretory peptide that induces melanin concentration within teleost melanophores. Here, we characterized MCH-like substance in the rat brain by both an in vitro fish-scale melanophore bioassay and a radioimmunoassay with a salmon MCH antiserum that is directed toward the carboxy-terminus and requires the cyclic configuration for recognition. Furthermore, subcellular localization of the MCH in the rat brain was examined by immunocytochemistry using electron microscopy. We confirmed that MCH-immunoreactivity and MCH-bioactivity were present together in the same effluent fractions of the rat hypothalamic extracts by reverse-phase high-performance liquid chromatography (HPLC). At electron microscopic level, MCH-immunoreactivity was located specifically in secretory granules in MCH-positive cell bodies confined to the hypothalamus with their neuronal processes projecting widely in the rat brain. Although full characterization of substance must await its isolation, our results strongly support the notion that rat MCH-like substance may be homologous but not identical to salmon MCH, and simultaneously may serve some neurotransmitter and/or neuromodulator role in the brain of the rat.

A sensitive bioassay for melanotropic hormones using isolated medaka melanophores

Melanophore-stimulating hormones (MSHs) from chum salmon cause pigment dispersion in isolated melanophores of medaka, a teleost. The in vitro medaka melanophore bioassay that responded to light with pigment dispersion and to the dark with pigment aggregation was utilized for measuring the activity of melanotropic hormones. alpha-MSH I was the most potent melanophore-dispersing agent tested. The minimal dose for the induction of pigment dispersion was 10(-15) M alpha-MSH I, 10(-13) M N-des-acetyl(Ac)-alpha-MSH, and 10(-11) M beta-MSH I, respectively. The melanosome-dispersing activity of beta-MSH I was enhanced about 40% by salmon N-acetyl-endorphin I (N-Ac-EP). The results suggest that N-Ac-EP may act as an enhancer for the activity of certain MSHs. The present bioassay provides a unique method for determining the biological activity of melanotropic peptides.