Cloning of pro-vasotocin and pro-isotocin cDNAs from the flounder Platichthys flesus; Levels of hypothalamic mRNA following acute osmotic challenge

Sequences coding for pro-vasotocin and pro-isotocin have been identified by screening a flounder (Platichthys flesus) hypothalamic cDNA library. The 1 074-bp proVT and 727-bp proIT sequences contain a signal peptide and hormon e, connected to a neurophysin by a Gly-Lys-Arg sequence. Both sequences als o have an elongated carboxyl-terminal with a leucine-rich core resembling c opeptin but lacking the amino terminal Arg residue. The levels of pro-vasot ocin and pro-isotocin mRNA in the hypothalamus were measured concomitantly with pituitary AVT content and plasma AVT concentration following acute tra nsfer of fish between freshwater and seawater. Three days after transfer fr om seawater to freshwater there appears to be a down regulation of the AVT hormone system with a fall in hypothalamic pro-vasotocin mRNA levels, an in crease in pituitary AVT content, and a fall in plasma levels, but these cha nges did not achieve statistical significance compared to controls. No chan ge in the AVT system was detected 3 days following the transfer of fish fro m freshwater to seawater. Hypothalamic isotocin mRNA levels did not change following hypo- or hyperosmotic challenge. (C) 2000 Academic Press.