Mu opioid receptor-like sequences are present throughout vertebrate evolution |
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Authors: | Xia Li Duane E Keith Jr Christopher J Evans |
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Institution: | (1) Department of Psychiatry and Biobehavioral Sciences, School of Medicine, University of California, Los Angeles, 760 Westwood Plaza, Los Angeles, CA 90024-1759, USA, US |
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Abstract: | The sequence of the mu opioid receptor is highly conserved among human, rat, and mouse. In order to gain insights into the
evolution of the mu opioid receptor, polymerase chain reaction (PCR) was used to screen genomic DNA from a number of different
species using degenerate oligonucleotides which recognize a highly conserved region. DNA was assayed from representative species
of both the protostome and deuterostome branches of the metazoan phylogenetic tree. Mu opioid receptor-like sequences were
found in all vertebrate species that were analyzed. These species included bovine, chicken, bullfrog, striped bass, thresher
shark, and Pacific hagfish. However, no mu opioid receptor-like sequences were detected from protostomes or from any invertebrates.
The PCR results demonstrate that the region of the mu opioid receptor gene between the first intracellular loop and the third
transmembrane domain (TM3) has been highly conserved during evolution and that mu opioid receptor-like sequences are present
in the earliest stages of vertebrate evolution. Additional opioid receptor-like sequence was obtained from mRNA isolated from
Pacific hagfish brain using rapid amplification of cDNA ends (RACE). The sequence of the Pacific hagfish was most homologous
with the human mu opioid receptor (72% at the amino acid level between intracellular loop 1 and transmembrane domain 6) although
over the same region high homology was also observed with the delta opioid receptor (69%), the kappa receptor (63%), and opioid
receptor-like (ORL1) (59%). The hagfish sequence showed low conservation with the mammalian opioid receptors in the first
and second extracellular loops but high conservation in the transmembrane and intracellular domains.
Received: 5 January 1996 / Accepted: 7 March 1996 |
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Keywords: | : Mu opioid receptor gene — Vertebrates — Molecular evolution |
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