African lungfish,Protopterus annectens, possess an arginine vasotocin receptor homologous to the tetrapod V2-type receptor

Abstract

SUMMARYIn tetrapods, arginine vasopressin and its counterpart, arginine vasotocin (AVT), are involved in renal water conservation through vascular V1a-type and tubular V2-type receptors, and only the former has thus far been cloned in fish. We successfully cloned the V1a-type and V2-type AVT receptor from the kidney of the African lungfish, Protopterus annectens, and the deduced amino acid sequences exhibited high homology with amphibian V1a-and V2-type receptors, respectively. Functional analysis showed that AVT addition to CHO cells transfected with lungfish V1a-type receptor increased [Ca 2+ ] i in a concentration-dependent manner, whereas CHO cells transfected with lungfish V2-type receptor responded with cAMP accumulation after AVT stimulation. Lungfish V2-type receptor mRNA was strongly expressed in the heart and kidney, while V1a-type receptor mRNA was ubiquitously expressed in all the tissues examined. In the kidney, immunohistochemistry using a specific antibody to lungfish V2-type receptor showed localization in the basolateral area of the cells in the late part of the distal tubules. Artificial estivation (EST) for 90 days significantly increased plasma osmolality and sodium and urea concentrations. There was no significant difference in the V2-type receptor mRNA and protein expression levels in the kidney between the freshwater and EST lungfish, while the AVT precursor mRNA level in the hypothalamus was remarkably higher in the EST lungfish. Our results indicate that African lungfish possess a functional V2-type receptor similar to that in tetrapods, suggesting that elevated plasma AVT during estivation exerts a renal tubular antidiuretic effect through the V2-type receptor expressed in the distal segments of lungfish kidney.

The oxytocin/vasopressin receptor family has at least five members in the gnathostome lineage, inclucing two distinct V2 subtypes

“…A putative V1B ortholog was found in the elephant shark, suggesting that V1B was lost in the teleost ancestor or even earlier in the ray-finned fish lineage. Because we have found all five ancestral subtypes in the genomes of a frog and a lizard, it is reasonable to expect that lungfishes and coelacanths may still possess a V1B-type ortholog as well, although to date only a V2-type receptor and one V1-type receptor have been identified in the African lungfish Protopterus annectens [25,26].…”

Vasotocin and isotocin regulate aquaporin 1 function in the sea bream

“…In fact, the expression of wildtype Aqp genes has previously been demonstrated to increase water P f values in Xenopus oocytes (Fushimi et al, , 1993Kuwahara et al, 1995;Yang and Verkman, 1997). AVT and IT receptors have recently been cloned in different teleost species, including the sea bream, and are considered to be relevant elements in osmoregulation (Konno et al, 2009;Lema, 2010;Martos-Sitcha et al, 2013). These receptors achieve the biological actions of the ligands via intracellular second-messenger pathways.…”

“…The endocrine effects of AVT and IT rely on the presence of membrane receptors that mediate the hormonal intrinsic information to carry out their physiological action. AVT and IT receptors (AVTR and ITR) have been cloned in some fish such as the Amargosa pupfish (Cyprinodon variegatus amargosae; Lema, 2010), the African lungfish (Protopterus annectens; Konno et al, 2009) and the gilthead sea bream (Sparus aurata, Martos-Sitcha et al, 2014;Martos-Sitcha et al, 2013). In the last of these, two AVTR types (V1a2-type and V2-type) and a single ITR are expressed in a wide range of organs/tissues, especially in those with an osmoregulatory role.…”

Amphibious fishes: evolution and phenotypic plasticity

“…In aestivating lungfish (Protopterus annectens), the hormone vasotocin may induce the upregulation of vasotocin V 2 receptor and aquaporin mRNA levels in the kidney to control water conservation (Konno et al, 2009(Konno et al, , 2010. The V 2 receptor gene shows high homology to amphibian sequences.…”