In:
Neuroendocrinology, S. Karger AG, Vol. 79, No. 4 ( 2004), p. 185-196
Abstract:
In mammals the opioids Met-enkephalin and Leu-enkephalin are derived from a common precursor, proenkephalin, and as a result these neuropeptides are co-localized in enkephalinergic neurons. The mammalian scheme for enkephalinergic networks is not universal for all classes of sarcopterygian vertebrates. In an earlier study, distinct Met- and Leu-enkephalin-positive neurons were detected in the central nervous system (CNS) of the African lungfish, 〈 i 〉 Protopterus annectens 〈 /i 〉 . More recently, characterization of proenkephalin cDNAs separately cloned from the CNS of 〈 i 〉 P. annectens 〈 /i 〉 and the Australian lungfish, 〈 i 〉 Neoceratodus forsteri 〈 /i 〉 , revealed that the proenkephalin gene in these species encodes only Met-enkephalin-related opioids. In the current study a full-length prodynorphin cDNA (accession No. AY 445637) was cloned and sequenced from the CNS of 〈 i 〉 N. forsteri 〈 /i 〉 . In addition to encoding α-neoendorphin, dynorphin A and dynorphin B sequences unique to the lungfish, two Leu-enkephalin sequences, flanked by paired basic amino acid proteolytic cleavage sites, were detected in this precursor. The partial sequence of a 〈 i 〉 P. annectens 〈 /i 〉 prodynorphin cDNA (accession No. AY445638) also encoded a Leu-enkephalin sequence and a novel YGGFF sequence. The presence of the Leu-enkephalin sequence in the lungfish prodynorphin precursors would explain the origin of the distinct Leu-enkephalin-positive neurons found in the African lungfish CNS. The realization that Met-enkephalin and Leu-enkephalin can be derived from distinct opioid-coding precursor genes calls into question the interpretation of comparative immunohistochemical studies that have mapped ‘enkephalinergic’ networks in non-mammalian vertebrates.
Type of Medium:
Online Resource
ISSN:
0028-3835
,
1423-0194
Language:
English
Publisher:
S. Karger AG
Publication Date:
2004
detail.hit.zdb_id:
1483028-0
Permalink