Charlotte Söderberg

Zebrafish genes for neuropeptide Y and peptide YY reveal origin by chromosome duplication from an ancestral gene linked to the homeobox cluster

Abstract: Neuropeptide Y (NPY) and peptide YY (PYY) are related 36‐amino acid peptides. NPY is widely distributed in the nervous system and has several physiological roles. PYY serves as an intestinal hormone as well as a neuropeptide. We report here cloning of the npy and pyy genes in zebrafish (Danio rerio). NPY differs at only one to four amino acid positions from NPY in other jawed vertebrates. Zebrafish PYY differs at three positions from PYY from other fishes and at 10 positions from mammals. In situ hybridization showed that neurons containing NPY mRNA have a widespread distribution in the brain, particularly in the telencephalon, optic tectum, and rhombencephalon. PYY mRNA was found mainly in brainstem neurons, as reported previously for vertebrates as divergent as the rat and the lamprey, suggesting an essential role for PYY in these neurons. PYY mRNA was observed also in the telencephalon. These results were confirmed by immunocytochemistry. As in the human, the npy gene is located adjacent to homeobox (hox) gene cluster A (copy a in zebrafish), whereas the pyy gene is located close to hoxBa. This suggests that npy and pyy arose from a common ancestral gene in a chromosomal duplication event that also involved the hox gene clusters. As zebrafish has seven hox clusters, it is possible that additional NPY family genes exist or have existed. Also, the NPY receptor system seems to be more complex in zebrafish than in mammals, with at least two receptor genes without known mammalian orthologues.

Evolution of the Neuropeptide Y Family of Peptides

Neuropeptide Y (NPY) is a member of a peptide family that also includes peptide YY (PYY), pancreatic polypeptide (PP), and fish pancreatic peptide Y (PY). This family of peptides is sometimes referred to as the pancreatic polypeptide family, since PP was the first of these to be discovered (1). However, we show here that NPY has remained much more conserved during evolution than W. This is why this peptide family should be more appropriately called the NPY family.

Neuropeptide Y receptor subtype with unique properties cloned in the zebrafish: the zYa receptor

Neuropeptide Y (NPY) belongs to a family of structurally related neuroendocrine peptides for which five different G-protein-coupled receptor subtypes have been cloned in mammals. To identify additional subtypes we have performed PCR with degenerate primers in different species. We describe here the cloning and pharmacological profile of a unique NPY receptor subtype in the zebrafish that has tentatively been called the zYa receptor. It has 46-50% amino acid identity to the mammalian Y1, Y4 and y6 receptors and the previously cloned zebrafish receptors zYb and zYc, and only about 27% to Y2 and Y5. The zYa receptor binds NPY and PYY from mammals as well as zebrafish with high affinities and has a K(d) of 28 pM for porcine (125)I-PYY. It has a unique binding profile displaying some features in common with each of the mammalian Y1, Y2 and Y5 receptors. In a microphysiometer assay the receptor responds with extracellular acidification. Chromosomal mapping in the zebrafish genome of zYa, zYb and zYc receptor genes indicates a possible orthologous relationship between zYc and mammalian y6, but identifies no obvious mammalian ortholog for zYa (zYb is a recent copy of zYc in the fish lineage). These results imply that previous studies of NPY in fishes, which have striven to interpret the effects within the framework of mammalian Y1, Y2, and Y5 receptors, need to be reevaluated. Thus, the sequence comparisons, pharmacological properties, and chromosomal localization suggest that the zYa receptor is a novel NPY receptor subtype which is likely to be present also in mammals.

Cloning of two loci for synapse protein Snap25 in zebrafish: Comparison of paralogous linkage groups suggests loss of one locus in the mammalian lineage

Synaptosome‐associated protein of 25 kDa (Snap25) is an intracellular protein that is defined as a target receptor for synapse vesicles prior to neurotransmitter release. Snap25 is highly conserved, with 61% identity between human and Drosophila melanogaster. Whereas mammals and chicken have a single locus for Snap25, the tetraploid goldfish has at least three loci. We report that the zebrafish has two loci with 91% amino acid identity to each other. The alternative splicing of exon 5 arose before the gene duplication. The expression patterns of the two loci are virtually identical in adult zebrafish. The two zebrafish snap25 loci are located in paralogous linkage groups that seem to correspond to human chromosome 20, which harbors the SNAP locus, and human chromosome 14. Because no additional Snap25 homologue has been reported for any mammal or chicken, snap25.2 may have been lost in the amniote or even tetrapod lineage. J. Neurosci. Res. 54:563–573, 1998.

Evolution of neuropeptide Y and its related peptides

1. The neuropeptide Y (NPY) family of peptides includes also the gut endocrine peptide YY (PYY), tetrapod pancreatic polypeptide (PP), and fish pancreatic peptide-tyrosine (PY). All peptides are 36 amino acids long. 2. Sequences from many types of vertebrates show that NPY has remained extremely well conserved throughout vertebrate evolution with 92% identity between mammals and cartilaginous fishes. 3. PYY has 97-100% identity between cartilaginous fishes and bony fishes, but is less conserved in amphibians and mammals (83% identity between amphibians and sharks and 75% identity between mammals and sharks). 4. NPY and PYY share 70-80% identity in most species. 5. Both NPY and PYY were present in the early vertebrate ancestor because both peptides have been found in lampreys. 6. The tissue distribution appears to have been largely conserved between phyla, except that PYY has more widespread neuronal expression in lower vertebrates. 7. Pancreatic polypeptide has diverged considerably among tetrapods leaving only 50% identity between mammals, birds/reptiles and frogs. 8. Several lines of evidence suggest that the PP gene arose by duplication of the PYY gene, probably in the early evolution of the tetrapods. 9. The pancreatic peptide PY found in anglerfish and daddy sculpin may have resulted from an independent duplication of the PYY gene. 10. The relationships of the recently described mollusc and worm peptides NPF and PYF with the NPY family still appear unclear.

Chapter 4 Peptidergic neurons in the vertebrate spinal cord: evolutionary trends

Publisher Summary This chapter discusses peptidergic neurons in the vertebrate spinal cord. The addresses four questions: (1) how the peptidergic neuron systems in the mammalian CNS evolved; (2) whether they were present in the earliest vertebrates, like many of the nonpeptide transmitter systems, or they appeared at later stages; (3) are the peptidergic systems similarly organized in all species, or do they differ; and (4) would they not only shed light on the evolution of the vertebrate CNS. In some instances, comparisons of peptide sequences among species have made it possible to deduce the mutational events during the evolution of a neuropeptide. However, in order to understand how a specific system of peptidergic neurons has evolved, it is necessary to compare its molecular features, anatomical organization, co-transmitters, target cells, and so on. Because of the anatomical differences between mammals and non-mammals, such comprehensive comparative analyses may be difficult to apply to certain CNS regions, such as the forebrain. In contrast, the spinal cord is well suited for this type of study, as its general outline can be recognized in all vertebrate classes, ranging from cyclostomes to primates. The organization, connectivity, and pharmacology of many spinal neuron systems have been thoroughly analyzed in several different vertebrates, thus providing a well-established framework for comparative studies. This chapter attempts to illustrate some trends in the evolution of spinal peptidergic neurons, by comparing the molecular and anatomical features of systems that have been characterized in mammals and in non-mammals.

A novel Mammalian homologue of a bacterial citrate-metabolizing enzyme.

Abstract: Mammals metabolize citrate to acetyl‐CoA and oxaloacetate via the enzyme, ATP:citrate lyase. Bacteria lack this enzyme, but have the ability to cleave citrate in the form of citryl‐CoA in an analogous manner using a structurally distinct enzyme. We have identified a novel mammalian gene that shows significant amino acid sequence homology to the bacterial CitE gene product that is responsible for cleavage of citryl‐CoA. We propose that this gene encodes an enzyme that catalyzes cleavage of substrates related to CoA esters of citrate or an analogous intermediary metabolite. The product of this novel gene may represent a component of an unknown metabolic pathway in mammals.

EVOLUTION OF THE NEUROPEPTIDE Y-PEPTIDE YY FAMILY

Neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP) form a family of 36-amino-acid peptides. DNA clones for NPY and PYY from several vertebrate species, including the river lamprey, show that both peptide genes were already present in the early vertebrate ancestor and that they have remained highly conserved during evolution. The PP gene probably arose as a copy of the PYY gene in early tetrapods. In situ hybridization shows that PYY expression is more widespread in the brain of lamprey than of mammals. We have cloned the zebrafish PYY (and NPY) gene to investigate whether this is a common feature among vertebrates. Clones have also been isolated for several NPY/PYY receptors in rat, human, and zebrafish to unravel the evolution of the receptor gene family. The results suggest that there may be at least four distinct receptor genes in bony fish and mammals.