<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.