Genomic approach in evaluating the role of androgens on the growth of Atlantic cod ( Gadus morhua) previtellogenic oocytes

Abstract

Previous studies have suggested that androgens may play an integral role in early oocyte development in fish. This study evaluated the effects of androgens (11-ketotestosterone: 11-KT and testosterone: T) on gene expression patterns and growth of cod previtellogenic oocytes. cDNA libraries of androgen-responsive genes were generated using suppressive subtractive hybridization (SSH) of clones containing differentially expressed genes in oocytes separately exposed to different concentrations of 11-KT and T, in addition to a solvent control. Secondly, a targeted microarray was developed based on differentially expressed genes. In the experimental setup, tissue was cultured in vitro with different concentrations of 11-KT and T (0, 10 and 100 μM). The array analyses showed 0.5–3.5-fold significant alterations in transcript levels for a number of genes. Real-time PCR and in -situ hybridization were also used to analyze the changes in expression for selected genes. Quantitative histological analyses showed a consistent stereological validation of oocyte growth and development after exposure to androgens. The present study reveals novel roles of androgens on the development of previtellogenic oocytes, suggesting androgen control of early oocyte growth in cod. The strong effects of 11-KT on oocyte growth support our hypothesis that non-aromatizable androgens may exert direct hormonal effects in previtellogenic oocytes, with possible consequences for overt fecundity.