Targeted cod (CodArray) gene chip: A genomic tool for evaluating the role of androgens on the growth of previtellogenic oocytes in Atlantic cod (Gadus morhua)
Prior to vitellogenesis (previtellogenesis), androgens appear to play pivotal roles in stimulating oocyte growth. In this study, suppression subtractive hybridization (SSH) with subsequent array development was used to open a possible revealing window in understanding the functional aspects of oocyte development. We constructed a targeted cod cDNA array containing 200 differentially-expressed genes using SSH after in vitro exposure of previtellogenic gonad tissue from Atlantic cod to a mixture of androgens. The targeted CodArray was hybridized using total RNA from cod previtellogenic oocyte cultures exposed to 11-ketotestosterone (11-KT) and testosterone (T) (0, 10 and 100 μM) for 5 and 10 days. Array analyses showed 0.5-3.5 -fold significantly altered transcript levels for a wide range of genes. Interestingly, T produced increased levels of zonadhesin and zona pellucida protein-2, whereas the levels of these genes were generally decreased after exposure to 11-KT. 11-KT produced apparent increases of cyclin-B, and suggests a control in the timing of the early embryonic cell cycle. Real-time PCR analysis confirmed the changes in expression for selected genes. In addition, quantitative histological analyses were used to investigate modulations of previtellogenic oocyte growth phases after androgen exposure. Our data show that both 11-KT and T are capable of inducing previtellogenic oocyte growth and development in vitro, with 11-KT being the strongest modulator. Taken together, the present study suggests some novel roles of androgens on the growth and development of previtellogenic oocytes, indicating possible androgen control of early follicular and oocyte growth in the cod ovary.