Isolation of Estrogen Receptor Subtypes and Vitellogenin Genes: Expression in Female Chalcalburnus Tarichi

Abstract

Reproductively arrested gonadal development has been previously described in the teleost 'pearl mullet (Chalcalburnus tarichi, Cyprinidae) from Van Edremit Gulf of Lake Van, Turkey. Oocyte development in some females was arrested at the previtellogenic stage, while gonadosomatic index (GSI) and plasma 17 beta-estradiol (E-2) level were low. A subset of the females was found to have normal ovaries and relatively higher plasma Ey and GSI. These two groups were termed reproductively arrested (RA) and reproductively non-arrested (RN) females. In this study, we cloned estrogen receptor (ER) isoforms (ER alpha, ER beta 1 and ER beta 2) and vitellogenin (Vtg), and their mRNA levels were measured in RA and RN fish tissues. C tarichi ERs fell in the same clade with other fish ERs and ERa and ER beta 1 had 97% and 98% identity with the roach (Rutilus rutilus) ERs, respectively. Both Vtg and ER isoforms' mRNA abundance were higher in the liver than in the ovary and hypothalamus (liver > ovary > hypothalamus). The level of ERa mRNA was significantly lower in the liver, ovary and brain of RA fish than in the RN fish tissues. ER beta 1 mRNA levels were not different in the liver and ovary from RA and RN fish while ER)32 expression significantly increased in the liver and ovary from RA fish. All ER subtype expression was found to be lower in the brain from RA fish than RN fish. The level of Vtg mRNA was significantly lower in the liver and ovary from RA fish than RN fish tissue. These results suggest that ER subtypes are differentially regulated by Ey, and their functions are also different in vitellogenesis. Analysis of organic contaminants in sediments revealed that C tarichi living in Van Edremit Gulf of Lake Van are exposed to the contaminants bis(2-ethylhexyl) phthalate and 4,4' DDT. We suggest that the RA fish represent a segment of the population that is more sensitive to exposure to endocrine disrupting compounds. (c) 2014 Elsevier Inc All rights reserved.