ABSTRACT
We recently showed that a series of tight junction proteins of the claudin family are regulated in the gill of salmon during salinity acclimation. The aim of the present study was to investigate the role of cortisol, growth hormone (GH) and prolactin (PRL) on regulation of expression of these isoforms. Experiments on primary cultures of gill tissue showed that cortisol stimulates claudin 10e, 27a and 30 mRNA levels while no significant effects were observed on claudin 28a and 28b. The associated receptor signalling pathway was examined using glucocorticoid and mineralocorticoid receptor antagonists RU486 and spironolactone, respectively. The observed in vitro responses were blocked by RU486, suggesting the involvement of a glucocorticoid type receptor. Injections of FW salmon with cortisol increased the expression of claudin 10e, 27a, and 30 but did not affect claudin 28a and 28b significantly. While GH had no effect on its own, the combination of GH and cortisol reduced claudin 28b levels. Injection of SW salmon with PRL selectively increased the expression of claudin 28a but had no effect on the other examined isoforms. The data shows that FW- (27a and 30) and SW-induced (10e) claudins are all stimulated by cortisol while the major osmoregulatory hormones GH and PRL had no effect on these salinity sensitive isoforms. This suggests that other hormones and/or osmotic conditions interact with cortisol to determine claudin composition in the gill.
Subject(s)
Gene Expression Regulation/drug effects , Gills/drug effects , Gills/metabolism , Growth Hormone/pharmacology , Hydrocortisone/pharmacology , Membrane Proteins/metabolism , Prolactin/pharmacology , Salmo salar/metabolism , Animals , Hormone Antagonists/pharmacology , Membrane Proteins/genetics , Mifepristone/pharmacology , Mineralocorticoid Receptor Antagonists/pharmacology , Polymerase Chain Reaction , Receptors, Glucocorticoid/antagonists & inhibitors , Receptors, Glucocorticoid/physiology , Receptors, Mineralocorticoid/physiology , Spironolactone/pharmacology , Water-Electrolyte Balance/drug effectsABSTRACT
It has been suggested that female birds put more resources into eggs fathered by attractive males by laying larger eggs or by adding more testosterone, but this inference could be undermined if eggs of different sex are provisioned differently, as these studies did not control for sex differences. Here we compare hormone concentrations in the yolks of male and female eggs and find that these are significantly different. Our results indicate that it is premature to conclude that female birds invest more in eggs sired by a preferred male, and raise the possibility that yolk sex steroids may be part of the sex-determining process in birds.
