Prolactin Directs Branchial and Intestinal Gene Expression of Solute Transporters and Aquaporins in Mummichog (Fundulus heteroclitus).

Mummichogs (Fundulus heteroclitus) can inhabit a wide range of environmental salinities because of their capacity to modulate the expression of genes that encode solute transporters and water channels within key osmoregulatory organs. Over 60 years ago, the pituitary hormone, prolactin (Prl), was identified as an essential factor that enables mummichogs to tolerate freshwater (FW) environments; nonetheless, the molecular targets of Prl signaling in this model teleost remain unknown. In the current study, we determined that two Prl receptors, designated prlra and prlrb, are expressed in osmoregulatory organs in salinity-dependent fashions. We administered ovine Prl (oPrl; 1 or 5 mg g body weight) by intraperitoneal injection to mummichogs held in brackish water (12 ppt) and first characterized the expression of genes associated with FW-type (ion absorptive) and seawater (SW)-type (ion secretory) ionocytes. Within FW-type ionocytes, oPrl stimulated the expression of Na /Cl cotransporter 2, aquaporin 3, and prlra. Branchial Na /H exchanger 2and -3 gene expression did not respond to oPrl. The expression levels of genes associated with SW-type ionocytes, such as Na /K /2Cl cotransporter 1and cystic fibrosis transmembrane regulator 1, were reduced following oPrl administration. Given the role of aquaporins in supporting fluid absorption by the intestine, we then assessed whether multiple aquaporin encoding genes were responsive to oPrl. We observed that aquaporin 1a and -8 were diminished by oPrl. As in the gill, oPrl stimulated the expression of prlra. Our collective data indicate that Prl promotes the survival of mummichogs in FW by simultaneously modulating a suite of genes within the gill and intestine that underlie critical ion- and water-transporting processes.