Expression of the Xenopus D₂ dopamine receptor

Abstract

In the amphibian Xenopus Zuevis the D, dopamine receptor is involved in the regulation of the melanotrope cells of the intermediate pituitary during background adaptation of the animal. The Xenopus D, receptor has been found to be pharmacologically different from the mammalian D, receptor. In a number of mammalian species alternative splicing generates two molecular forms of the D, receptor. These isoforms differ by the presence or absence of 29 amino acids in the third cytoplasmic loop which is thought to be involved in guanine-nucleotide-binding-regulatory-protein (G-protein) binding of the receptor. We previously described a cDNA encoding the large isoform of the Xenopus D, receptor. Here we report on the isolation of a brain cDNA encoding a second, structurally different Xenopus D, dopamine receptor. Both Xenopus receptors correspond to the large isoform of the D, receptor and they display a high degree of sequence identity with their mammalian counterparts. Their occurrence reflects the expression of two Xenopus D, receptor genes and they are expressed to approximately the same level. In contrast to mammals, PCR analysis gave no evidence for alternative splicing during D, receptor expression in Xenopus brain and pituitary. Tissue-specific expression of the Xenopus D, receptor was observed in the pituitary during background adaptation. The low level of receptor mRNA in melanotrope cells of white animals compared to that of black animals may be caused by chronic dopamine stimulation of melanotrope cells in white animals with consequent cellular desensitization and down regulation of the D, receptor gene.Recent cloning of cDNA and genomic DNA fragments has revealed the existence of a number of dopamine-receptor subtypes, namely the D1, D,, DS, D, and D, receptors [l-71. These receptors, which belong to the family of guaninenucleotide-binding-regulatory-protein(G-protein)-coupled receptors, are characterized by the presence of seven putative membrane-spanning domains within their structures [S]. The diversity of dopamine receptors is probably generated by gene duplication events. The D, and D, receptors are structurally and functionally related, and they are encoded by intronless genes. In contrast, the genes encoding the structurally and functionally related D,, D, and D, receptors all contain a number of introns. The structural and functional relationships between the dopamine-receptor subtypes D, and D, on the one hand, and DZ, D, and D4 on the other, may reflect their evolutionary history. In human, bovine, rat and Note. The novel nucleotide sequence data published here has beeen deposited with the EMBL sequence data banks and is available under accession number X72902. mouse the degree of diversity of dopamine-receptor subtypes is further increased by alternative splicing of D,-dopaminereceptor-gene transcripts which results in D, , and D,, receptor subtypes [9-131. The D, receptor isoforms differ from each other by the presence or absence of 29 amino-acid residues in the third cytoplasmic loop. Cells tran...

Distribution of dopamine D2 receptor mRNAs in the brain and the pituitary of female rainbow trout: An in situ hybridization study

“…AJ347728 and AJ347729; Vacher, 2001). These two sequences correspond to the mammalian long isoform, because no evidence for the presence of an alternative splicing of exon 6, generating a short isoform deleted from 29 amino acids in the third intracytoplasmic loop, has been found in trout (Vacher, 2001), similar to the fugu (Macrae and Brenner, 1995) and Xenopus (Martens et al, 1993). These cDNA sequences share 96% of identity and for our in situ hybridization experiments, we used an 810-bp probe that equally hybridizes with the two corresponding messenger species as shown by the dot-blot assay.…”

“…AJ347728 and AJ347729; Vacher, 2001). Sequence identities and conserved positions of putative functional amino acids pointed out in fugu (Macrae and Brenner, 1995), carp (Hirano et al, 1998), Xenopus (Martens et al, 1993), turkey (Schnell et al, 1999), and mammals (Myeong et al, 2000) indicate that both trout sequences belong to the D 2 R subtype. In the present study, we report for the first time the distribution of D 2 receptor mRNAs in the brain and pituitary of a teleost species, the rainbow trout.…”

“…To date, the central distribution of DA receptors is documented in only one fish species, the eel; and this study is limited to subtypes of the D 1 receptors (Kapsimali et al, 2000). Dopamine D 2 R have also been cloned in Xenopus, but there is no information on their central distribution (Martens et al, 1993).…”

Comparative Analysis and Expression of Neuroserpin in <i>Xenopus laevis</i>

“…1A). A number of other Xenopus protein pairs have been shown to occur, including for POMC [19], prohormone convertase PC2 [20], amyloid precursor protein APP [21], D2 dopamine receptor [22] and serum albumins [23], and these pairs are present because a whole-genome duplication event has occurred in the species X. laevis ∼35 million years ago [24]. Since the magnitude of sequence identity observed between the two Xenopus neuroserpin proteins (95%) is similar to those found for the other Xenopus protein pairs (92–95%), it is likely that the two Xenopus neuroserpins do not correspond to allelic variants but rather that they are also the result of the genome duplication.…”

D1A, D1B, and D1C dopamine receptors from Xenopus laevis.

“…preproinsulins, proopiomelanocortins, and proenkephalins which share 92-95% nucleotide and amino acid identity (42)(43)(44)(45)(46). The low homologies displayed between the members of the Xenopus D1 receptor family suggest that they diverged prior to the predicted duplication event, in accord with the proposed early evolutionary appearance (=500 million years) and ancient status of the DI-like receptor subfamily (33).…”