cDNA Cloning and Functional Expression of a Ca2+-sensing Receptor with Truncated C-terminal Tail from the Mozambique Tilapia (Oreochromis mossambicus)

Abstract

The complete cDNA sequence of the tilapia extracellular Ca 2؉ -sensing receptor (CaR) was determined. The transcript length of tilapia CaR (tCaR) is 3.4 kbp and encodes a 940-amino acid, 7-transmembrane domain protein that is consistent in its structural features with known mammalian and piscine CaRs. The tCaR extracellular domain includes a characteristic hydrophobic segment, conserved cysteine residues that are implicated in receptor dimerization (Cys 129 and Cys 131 ) and in coupling to the transmembrane domain (nine conserved cysteine residues), and conserved serine residues (Ser 147 and The roles for ionic calcium (Ca 2ϩ ) in physiological functions are many and varied and essential for survival. Ca 2ϩ -dependent cellular processes include hormone secretion (stimulussecretion coupling), excitability and cell motility (excitationcontraction coupling), and neurotransmission (Ca 2ϩ -based action potentials). This critical involvement of Ca 2ϩ in these and other cellular functions is unique among ions. Ca 2ϩ is simultaneously a controlled variable in physiological systems, an extracellular messenger in multicellular organisms, and an intracellular mediator in a variety of effector cells.Unicellular organisms acquire Ca 2ϩ from the external environment; they have little control over the composition of the surrounding medium and thus had to evolve plasma membrane-bound and other cellular mechanisms to realize cellular Ca 2ϩ homeostasis eventually permitting some degree of habitat survival and selection. In multicellular organisms, active regulation by integumentary tissues of the composition of an "extracellular fluid," which bathes all cells, assures a constant internal milieu and contributes to normal Ca 2ϩ -dependent cell functions. In terrestrial vertebrates, Ca 2ϩ homeostasis depends upon appropriate dietary intake, renal output, and osseous storage and mobilization of Ca 2ϩ . These processes are well known and are regulated by parathyroid hormone, calcitonin, and 1,25-dihydroxyvitamin D acting on kidney, intestine, and bone. Activation of the Ca 2ϩ -sensing receptor (CaR) 1 by its natural ligand, extracellular Ca 2ϩ , alters parathyroid hormone and calcitonin secretion and inhibits renal 1-hydroxylase to retard the synthesis of 1,25-dihydroxyvitamin D (1, 2). Ca 2ϩ balance is achieved through regulated calciotropic hormone secretion in response to the extracellular Ca 2ϩ concentration ([Ca 2ϩ ] o ); the secreted hormones, in turn, control the activity of Ca 2ϩ -transporting tissues to bring about alterations in [Ca 2ϩ ] o . Interestingly, in fishes, the calcium homeostatic process involves ion-transporting tissues not represented in other vertebrate classes (viz., the mitochondria-rich "chloride cells" of the gills and skin) and a different panel of hormones (prolactin and somatolactin from the pituitary, and stanniocalcin from the piscine corpuscles of Stannius (3)). Opportunities for cutaneous

Activation of gill Ca2+-sensing receptor as a protective pathway to reduce Ca2+-induced cytotoxicity

“…In this study, we provided evidence that the treatment of cells with Ca 2C or Ca 2C /calcimimetics activated PLC-ERK and IP 3 -CaMK2 pathways. The data on PLC-ERK activation are consistent with reports on ectopic expression of tilapia or human CaSR in embryonic kidney cells (Loretz et al 2004, Davies et al 2006 or in bovine parathyroid cells respectively (Kifor et al 2001). Although the activation of CaSR-induced PLC-IP 3 signaling in fish tissues has not been reported previously, a recent study using isolated mouse juxtaglomerular cells described this post-receptor IP 3 pathway (Ortiz-Capisano et al 2013).…”

“…In the present study, our western blotting analysis data support the presence of Casr expression in gill tissues of Japanese eels. The molecular size of the eel Casr protein is similar to the expected molecular mass of non-glycosylated Casr core protein in tilapia (Loretz et al 2004). Moreover the treatment of isolated gill cells with Ca 2C or Ca 2C / calcimimetics activated the conserved CaSR-mediated pathways to increase PLC activity and ERK-and IP 3 / CaMK2-signaling.…”

“…In mammalian models, sensitivity of CaSR to Ca 2C was affected by local ionic strength and pH (Quinn et al 1998(Quinn et al , 2004, where the activation of CaSR results in the stimulation of PLC and Ca 2C mobilization (Hofer & Brown 2003). A number of studies have reported the expression of CaSR in iontransporting tissues (i.e., gill, kidney, and intestine) in shark (Nearing et al 2002), tilapia (Loretz et al 2004), and flounder (Greenwood et al 2009). Although the expression of CaSR was found to be associated with ion (Ca 2C , Mg 2C , and Na C ) sensing (Nearing et al 2002), downstream responses following CaSR-activation were not known.…”

Physiological mechanisms used by fish to cope with salinity stress

“…Not surprisingly, posttranslational modifications such as phosphorylation represent a prominent mechanism for osmosensory signal transduction. For instance, phospholipase C (PLC) and mitogen-activated protein kinase (MAPK) signaling pathways are involved in osmosensing in tilapia (Loretz et al, 2004). MAPK pathways also play a role in osmosensing in killifish and turbot (Kültz and Avila, 2001;Marshall et al, 2005).…”

cDNA Cloning and Expression of the Cardiac Na+/Ca2+ Exchanger from Mozambique Tilapia (Oreochromis mossambicus) Reveal a Teleost Membrane Transporter with Mammalian Temperature Dependence

“…are euryhaline teleosts that inhabit environments ranging from freshwater to seawater of high salinity and can withstand temperatures as high as 42°C (31,32). Due to their tolerance of relatively extreme environments, tilapias have gained important roles as model organisms in the laboratory (31,33,34) and as a prominent fish in aquaculture (32,35). In this study, we have chosen the Mozambique tilapia (Oreochromis mossambicus) as a model system because the cardiac NCX from this species has likely adapted to function at temperatures similar to those in the mammalian heart, but lethal to trout.…”