Acute salinity tolerance and the control of two prolactins and their receptors in the Nile tilapia (Oreochromis niloticus) and Mozambique tilapia (O. mossambicus): A comparative study

Abstract

Osmoregulation in vertebrates is largely controlled by the neuroendocrine system. Prolactin (PRL) is critical for the survival of euryhaline teleosts in fresh water by promoting ion retention. In the euryhaline Mozambique tilapia (Oreochromis mossambicus), pituitary PRL cells release two PRL isoforms, PRL and PRL, in response to a fall in extracellular osmolality. Both PRLs function via two PRL receptors (PRLRs) denoted PRLR1 and PRLR2. We conducted a comparative study using the Nile tilapia (O. niloticus), a close relative of Mozambique tilapia that is less tolerant to increases in environmental salinity, to investigate the regulation of PRLs and PRLRs upon acute hyperosmotic challenges in vivo and in vitro. We hypothesized that differences in the regulation of PRLs and PRLRs underlie the variation in salinity tolerance of tilapias within the genus Oreochromis. When transferred from fresh water to brackish water (20‰), Nile tilapia increased plasma osmolality and decreased circulating PRLs, especially PRL, to a greater extent than Mozambique tilapia. In dispersed PRL cell incubations, the release of both PRLs was less sensitive to variations in medium osmolality in Nile tilapia than in Mozambique tilapia. By contrast, increases in pituitary and branchial prlr2 gene expression in response to a rise in extracellular osmolality were more pronounced in Nile tilapia relative to its congener, both in vitro and in vivo. Together, these results support the conclusion that inter-specific differences in salinity tolerance between the two tilapia congeners are tied, at least in part, to the distinct responses of both PRLs and their receptors to osmotic stimuli.

Molecular and Histological Studies of Salinity effect on gills and liver of Coptodon zillii in Egypt

“…In the present study, levels of PRLR mRNA relative to BA mRNA (PRLR/BA) in pituitary gland of C. zilli were significantly higher in fish kept in fresh water (FW) than in those in saline water (SW). This is consistent with the change in PRLR mRNA in the pituitary gland following transfer of Nile tilapia to blackish water (20‰), as measured by Northern-blot analysis (Sandra et al, 1995, Yamaguchi et al, 2018. The expression of PRLR mRNA in the pituitary gland seems to be upregulated by the higher levels of circulating PRLs present in FW than in SW or in blackish water (Ayson et al, 1993;Auperin et al, 1994).…”

Transcriptomic response to three osmotic stresses in gills of hybrid tilapia (Oreochromis mossambicus female × O. urolepis hornorum male)

“…Zhu et al found that the NKAα1 mRNA expression levels in the gills of tilapia reached peak level at 24 h after transfer from freshwater to seawater [45]. Yoko et al research showed that PRLR2 facilitates acclimation responses to increased extracellular osmolality [46]. Yuan et al observed the synchronous expression trend of the renal PRLR with pituitary PRL (5d) and the asynchronous expression peaks between branchial (8d) and renal PRLR (5d) in olive flounder Paralichthys olivaceus, and the mRNA levels of PRL receptor (PRLR) in both gill and kidney displayed a similar trend to the pituitary PRL [47].…”

Blood physiological responses and steroidogenetic effects of decreasing salinity on maturing male spotted sea bass (Lateolabrax maculatus )

“…Prolactin (PRL) and its receptor (PRLR) are critical for the survival of euryhaline teleost involving in ion uptake (Juan et al, 2002;Yamaguchi et al, 2017). Besides, cortisol plays a very important role in stress adaptation involving in immune, metabolism and other biological process (Szisch, Papandroulakis, Fanouraki, & Pavlidis, 2005), and its intracellular receptors glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) exert their corresponding biological processes after binding with serum cortisol (Prunet, Sturm, & Milla, 2006).…”

“…Osmoregulation has been studied in many euryhaline teleosts, such as black porgy Acanthopagrus schlegeli (Tomy et al, 2009), golden pompano trachinotus ovatus (Ma et al, 2016), black-chinned tilapia (Sarotherodon melanotheron) (Tine, Guinand, & Durand, 2012) and salmonids (Flores & Shrimpton, 2012;McCormick, Regish, & Christensen, 2009). Prolactin (PRL) and its receptor (PRLR) are critical for the survival of euryhaline teleost involving in ion uptake (Juan et al, 2002;Yamaguchi et al, 2017). Besides, cortisol plays a very important role in stress adaptation involving in immune, metabolism and other biological process (Szisch, Papandroulakis, Fanouraki, & Pavlidis, 2005), and its intracellular receptors glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) exert their corresponding biological processes after binding with serum cortisol (Prunet, Sturm, & Milla, 2006).…”