Effects of Water Temperature and Food Limitation on Pituitary Gonadotropin and Thyrotropin Subunit mRNA Levels in the Female Goldfish Carassius auratus

抄録

Water temperature and the nutritional status of individual fish have a profound effect on the reproductive activities that are mainly mediated by the brain-pituitary-gonad endocrine system. In order to investigate the influence of environmental factors on the expression of gonadotropin (GTH) and thyrotropin (TSH) subunit genes in the pituitary, we examined the effects of temperature manipulation and a limitation of food on mRNA levels for GTH I, GTH II, and TSH subunits in sexually mature female goldfish by Northern blot analysis. After fish were acclimated at 20°C, the fish were maintained at either 10, 20, or 30°C for two weeks. The mRNA levels for the a and GTH Iβ subunits were observed to be higher at 10°C than at 20 or 30°C. In contrast, mRNA levels for the GTH IIβ subunit were not different at those temperatures. Low levels of TSHβ mRNA were observed in fish held at 30°C compared to those held at 10 and 20°C. Although fish were unfed for two weeks, no marked differences were observed in mRNA levels of all the GTH and TSH subunits between unfed and fed fish. These data suggest that, in mature female goldfish, low temperature has a stimulating effect on expressions of α, GTH Iβ, and TSHβ genes, and a limitation of food has no significant effect on expression of the examined GTH and TSH subunit genes at least during two weeks.