The basal function of teleost prolactin as a key regulator on ion uptake identified with zebrafish knockout models

Abstract

Prolactin (PRL) is an anterior pituitary hormone with a broad range of functions. Its ability to stimulate lactogenesis, maternal behavior, growth and development, osmoregulation, and epithelial ion transport has been reported in many vertebrates. In our present study, we have targeted the zebrafish prl locus via transcription activator-like effector nucleases (TALENs). Two independent targeted mutant lines with premature termination of the putative sequence of PRL peptides were generated. All prl-deficient zebrafish progeny died at 6–16 days post-fertilization stage (dpf) in egg water. However, the prl-deficient larvae thrived and survived through adulthood in brackish water (5175 mg/L ocean salts), without obvious defects in somatic growth or reproduction. When raised in egg water, the expression levels of certain key Na+/Cl− cotransporters in the gills and Na+/K+-ATPase subunits, Na+/H+ exchangers and Na+/Cl− transporters in the pronephros of prl-deficient larvae were down-regulated at 5 dpf, which caused Na+/K+/Cl− uptake defects in the mutant fish at 6 dpf. Our present results demonstrate that the primary function of zebrafish prl is osmoregulation via governing the uptake and homeostasis of Na+, K+ and Cl−. Our study provides valuable evidence to understand the mechanisms of PRL function better through both phylogenetic and physiological perspectives.

Neuroendocrine control of ionic balance in zebrafish

“…The prolactin-deficient larvae at 6 dpf had lower whole body levels of Na + , K + and Cl − when compared to the wild-type fish (Shu et al, 2016). Interestingly, the reduction in whole body ion levels in the prolactin-deficient zebrafish was prevented when they were raised in ion-enriched water (163 mOsm/L), allowing them to survive into adults (Shu et al, 2016).…”

“…The prolactin-deficient larvae at 6 dpf had lower whole body levels of Na + , K + and Cl − when compared to the wild-type fish (Shu et al, 2016). Interestingly, the reduction in whole body ion levels in the prolactin-deficient zebrafish was prevented when they were raised in ion-enriched water (163 mOsm/L), allowing them to survive into adults (Shu et al, 2016). Additionally, a decrease in the mRNA expression levels of ncc but increased expression levels of atp1a1a.5 (an HRC marker) was observed in prolactin-deficient zebrafish larvae (Shu et al, 2016).…”

“…In larval zebrafish, prolactin is expressed in the anterior pituitary (Liu et al, 2006;Sbrogna et al, 2003), and its receptors (prlra and prlrb) are abundantly expressed in both the developing gills and kidney (Shu et al, 2016). In adult zebrafish, these receptors are expressed in osmoregulatory organs, including the gills, kidney and intestine (Breves et al, 2013b).…”

“…Using a line of prolactin-knockout mutants, it was further demonstrated that prolactindeficient larvae could not survive to the adult stage when they were raised in typical freshwater (2 mOsm/L) (Shu et al, 2016). The prolactin-deficient larvae at 6 dpf had lower whole body levels of Na + , K + and Cl − when compared to the wild-type fish (Shu et al, 2016).…”

“…Interestingly, the reduction in whole body ion levels in the prolactin-deficient zebrafish was prevented when they were raised in ion-enriched water (163 mOsm/L), allowing them to survive into adults (Shu et al, 2016). Additionally, a decrease in the mRNA expression levels of ncc but increased expression levels of atp1a1a.5 (an HRC marker) was observed in prolactin-deficient zebrafish larvae (Shu et al, 2016). Overall, these studies demonstrate an important role of prolactin in maintaining ionic balance and survival during early development, at least in part via its regulation of the expression of NCC.…”