Cloning of Prodynorphin cDNAs from the Brain of Australian and African Lungfish: Implications for the Evolution of the Prodynorphin Gene

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, Protopterus annectens. More recently, characterization of proenkephalin cDNAs separately cloned from the CNS of P. annectens and the Australian lungfish, Neoceratodus forsteri, 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 N. forsteri. 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 P. annectens 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.

Genetic and functional analysis of a Pacific hagfish opioid system

“…It is unclear if the antisera used for Leu-enkephalin in this study would distinguish leucine from isoleucine-enkephalin as we would predict would be a cleavage product of esPENKL2. A separation of the genes encoding of Met-enkephalin and Leu-enkephalin into two genes has already been observed in several non-mammalian vertebrate species (Dores et al, 2004).…”

Functional Characterization and Molecular Marker Development of the Proenkephalin as Biomarker of Food Addiction in Food Habit Domestication of Mandarin Fish (Siniperca chuatsi)

“…PENK-derived ENKs act as endogenous ligands for δand µ-opioid receptors, which may be involved in emotion regulation activities, such as euphoria, and rewarding behavior [15,16]. Studies have shown that the PENK gene is involved in addiction and rewarding behavior [17,18]. Although the positive neurons of Mek and Lek have been significantly detected in the nervous system of African lungfish [19], Penk has not been extensively characterized in mandarin fish.…”

Dynorphin regulates the phagocytic activity of splenic phagocytes in wall lizards: involvement of a κ-opioid receptor-coupled adenylate-cyclase–cAMP–PKA pathway

“…Dynorphins are endogenous opioid peptides encoded by a common proenkaphalin-B gene (hereafter referred to as preprodynorphin, PDYN) (Civelli et al, 1985) that is widely expressed in the central and peripheral nervous systems of vertebrates (Cone et al, 1982;Goldsmith et al, 1992;Dores et al, 2004;Shirayama et al, 2004;Alrubaian et al, 2006). As for various peptide hormones, dynorphins are synthesized as large, biologically inert precursor proteins that undergo post-translational modifications to produce biologically active molecules.…”

“…Cloning and sequence analysis of the preprodynorphin cDNA revealed that it is a highly conserved gene, although some discrepancies have been described in lower ectotherms. In fish and amphibians, the gene encoding PDYN contains an additional opioid sequence for leucine-enkephalin or isoleucine-enkephalin (Dores et al, 2004;Alrubaian et al, 2006) and for methionine-enkephalin (Danielson et al, 2002), respectively. Although the gene encoding PDYN has not been cloned to date in reptiles, different dynorphins such as -neo-endorphin, dynorphin A (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17) , dynorphin A (1)(2)(3)(4)(5)(6)(7)(8) and dynorphin B (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13) in the lizard Anolis carolinensis and -neo-endorphin and dynorphin B (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13) in turtle and alligator have been demonstrated by Goldsmith and colleagues …”