Prolactin as an osmoregulatory hormone in zebrafish: transcriptional regulation of a Na+/Cl− cotransporter (ncc) in the gill

Abstract

Prolactin (PRL) is a well‐known regulator of ion and water transport within osmoregulatory tissues across vertebrate species, yet how PRL acts on some of its targets remains poorly understood. Along with the genetic and experimental accessibility of the zebrafish (Danio rerio) model, the high capacity for ion‐uptake exhibited by this freshwater teleost positions them as a powerful model for studies aimed at elucidating how the endocrine system governs effectors of ion transport. Here, we show that ionocytes in the gill may directly respond to systemic PRL to regulate ion uptake. Ion‐poor conditions led to increases in the expression of PRL receptor (prlra), Na+/Cl− cotransporter (ncc; slc12a10.2), Na+/H+ exchanger (nhe3b), and epithelial Ca2+ channel (ecac) transcripts within the gill. Intraperitoneal injection of ovine PRL (oPRL) increased ncc and prlra transcripts, but did not affect nhe3b or ecac. Consistent with direct action, the addition of oPRL to cultured gill filaments stimulated ncc in a concentration‐dependent manner, an effect blocked by a pure human PRL receptor antagonist (Δ1–9‐G129R‐hPRL). These results suggest that endocrine PRL signaling through PRL receptors regulates ncc expression, thereby suggesting PRL may be a key hormonal regulator of Cl− uptake mechanisms in zebrafish gill. Supported by NIH [T32‐MH020051–07 and F32‐DK095575].