<p>Neuropeptide Y (NPY) is an abundant neurotransmitter in the nervous system and forms a family of evolutionarily related peptides together with peptide YY (PYY), pancreatic polypeptide (PP) and polypeptide Y (PY). These peptides are ligands to a family of receptors that mediate a wide range of physiological effects including stimulation of appetite. This work describes the molecular cloning of four novel NPY receptors.</p><p>In rat a receptor called PP1, later renamed Y₄, was cloned and characterized. It displays the highest amino acid sequence identity to the Y₁ receptor. Rat Y₄ differs extensively from human Y₄, cloned subsequently, in both pharmacological properties, tissue distribution, and amino acid sequence with only 75% identity. Rat and human Y₄are the most diverged orthologues in the NPY receptor family.</p><p>In guinea pig, the y₆ receptor gene was found to be a pseudogene with several frameshift mutations. The gene is a pseudogene in human and pig too, but seems to give rise to a functional receptor in mouse and rabbit. This unusual evolutionary situa- tion may be due to inactivation of the gene in a mammalian ancestor and then restoration of expression in mouse and rabbit, but perhaps more likely due to independent inactivations in guinea pig, human and pig.</p><p>In zebrafish, two new intronless receptor genes were cloned. Sequence comparisons suggest that both receptors are distinct from the mammalian receptors Y₁, Y₄ and y₆, hence they were named Ya and Yb. Chromosomal localization provides further support that Ya and Yb may be distinct subtypes. </p><p>The discoveries of the rat Y₄ and zebrafish Ya and Yb receptors were unexpected and show that the NPY receptor family is larger than previously thought.</p>

Neuropeptide Y (NPY) is an abundant neurotransmitter in the nervous system and forms a family of evolutionarily related peptides together with peptide YY (PYY), pancreatic polypeptide (PP) and polypeptide Y (PY). These peptides are ligands to a family of receptors that mediate a wide range of physiological effects including stimulation of appetite. This work describes the molecular cloning of four novel NPY receptors. In rat a receptor called PP1, later renamed Y4, was cloned and characterized. It displays the highest amino acid sequence identity to the Y1 receptor. Rat Y4 differs extensively from human Y4, cloned subsequently, in both pharmacological properties, tissue distribution, and amino acid sequence with only 75% identity. Rat and human Y4 are the most diverged orthologues in the NPY receptor family. In guinea pig, the y6 receptor gene was found to be a pseudogene with several frameshift mutations. The gene is a pseudogene in human and pig too, but seems to give rise to a functional receptor in mouse and rabbit. This unusual evolutionary situa- tion may be due to inactivation of the gene in a mammalian ancestor and then restoration of expression in mouse and rabbit, but perhaps more likely due to independent inactivations in guinea pig, human and pig. In zebrafish, two new intronless receptor genes were cloned. Sequence comparisons suggest that both receptors are distinct from the mammalian receptors Y1, Y4 and y6, hence they were named Ya and Yb. Chromosomal localization provides further support that Ya and Yb may be distinct subtypes. The discoveries of the rat Y4 and zebrafish Ya and Yb receptors were unexpected and show that the NPY receptor family is larger than previously thought.

<p>Neuropeptide Y (NPY) is known to influence a vast number of physiological and behavioral processes such as vasoconstriction, circadian rhythms, feeding, anxiety and memory. Peptides of the NPY family bind to five different cloned G-protein coupled receptor subtypes (Y1, 2, 4-6). The studies compiled in this thesis present inter-species comparisons of sequence similarities, binding properties and expression patterns among receptors of the NPY family.</p><p>Cloning of Y1 and Y2 receptor subtypes from guinea pigs revealed strong binding profile similarity to the corresponding human receptors. Previously demonstrated atypical binding profiles in the caval vein of guinea pigs were concluded to result from other receptors than the cloned Y1 and Y2 receptors, or possibly combinations of distinct receptor subtypes.</p><p>The guinea pig Y5 receptor was found to be expressed in regions of the brain that have been indicated as important for regulation of food intake. Expression in the hypothalamus, amygdala and brain stem was noticed, similar to studies in rats and humans. In other brain regions, such as the striatum and hippocampus, some species differences were observed.</p><p>Mutagenesis studies of the human Y1 receptor indicated sites important for binding both of endogenous agonists and synthetic antagonists. Putative new sites of interaction with the Y1 antagonists BIBP3226 and/or SR120819A were recognized. The data were used to construct a three-dimensional structure model, based on a high-resolution bovine rhodopsin model.</p><p>Cloning of the chicken (<i>Gallus gallus</i>) Y1, Y2 and Y5 receptors revealed high sequence similarities with mammalian receptors. Most endogenous ligands bound with similar affinities as to mammalian receptors. The strongest exception was the discovery of high-affinity binding to chicken Y2 of [Leu³¹, Pro³⁴]NPY, which was previously considered to bind non-Y2 receptors only. </p><p>The new human Y1 receptor model provides a basis for further investigations of ligand-receptor interactions which will be aided by information on NPY receptors from other taxa. Guinea pigs are concluded to be a good complement to rats and mice for studying NPY signaling. These results demonstrate the benefits of species comparisons for pharmacological studies.</p>

Neuropeptide Y (NPY) is known to influence a vast number of physiological and behavioral processes such as vasoconstriction, circadian rhythms, feeding, anxiety and memory. Peptides of the NPY family bind to five different cloned G-protein coupled receptor subtypes (Y1, 2, 4-6). The studies compiled in this thesis present inter-species comparisons of sequence similarities, binding properties and expression patterns among receptors of the NPY family. Cloning of Y1 and Y2 receptor subtypes from guinea pigs revealed strong binding profile similarity to the corresponding human receptors. Previously demonstrated atypical binding profiles in the caval vein of guinea pigs were concluded to result from other receptors than the cloned Y1 and Y2 receptors, or possibly combinations of distinct receptor subtypes. The guinea pig Y5 receptor was found to be expressed in regions of the brain that have been indicated as important for regulation of food intake. Expression in the hypothalamus, amygdala and brain stem was noticed, similar to studies in rats and humans. In other brain regions, such as the striatum and hippocampus, some species differences were observed. Mutagenesis studies of the human Y1 receptor indicated sites important for binding both of endogenous agonists and synthetic antagonists. Putative new sites of interaction with the Y1 antagonists BIBP3226 and/or SR120819A were recognized. The data were used to construct a three-dimensional structure model, based on a high-resolution bovine rhodopsin model. Cloning of the chicken (Gallus gallus) Y1, Y2 and Y5 receptors revealed high sequence similarities with mammalian receptors. Most endogenous ligands bound with similar affinities as to mammalian receptors. The strongest exception was the discovery of high-affinity binding to chicken Y2 of [Leu31, Pro34]NPY, which was previously considered to bind non-Y2 receptors only. The new human Y1 receptor model provides a basis for further investigations of ligand-receptor interactions which will be aided by information on NPY receptors from other taxa. Guinea pigs are concluded to be a good complement to rats and mice for studying NPY signaling. These results demonstrate the benefits of species comparisons for pharmacological studies.