Global Gene Expression Profiling in the Hypothalamus and the Pituitary of the Pacific Bluefin Tuna using Next-generation Sequencing

The Pacific bluefin tuna (Thunnus orientalis) aquaculture has expanded and developed as an important commercial enterprise in Japan.  Pacific bluefin tuna typically spawn in June to September under the culture conditions in Japan.  However, the detail mechanisms of ovarian maturation remains poorly understood.  In order to achieve further development of tuna aquaculture, it is necessary to elucidate the mechanisms of ovarian maturation.  Currently accepted model of reproductive regulation is the hypothalamic-pituitary-gonad (HPG) axis.  In particular, the hypothalamus and the pituitary are the central organs for controlling ovarian maturation.  Thus, we performed global gene expression analyses in the hypothalamus and the pituitary using next-generation sequencing.  Complementary DNA was synthesized from mRNA of female tuna that were sampled during different seasons.  Gene expression was profiled using whole genome sequence data, which our research group has reported recently.  In the hypothalamus, cytoskeleton-associated genes were highly expressed.  On the other hand, pituitary hormone genes were highly expressed in the pituitary and the expression patterns of pituitary hormone genes were varied according to ovary maturation.  Our results will lead to the elucidation of reproductive mechanisms of tuna and will contribute to further development of tuna aquaculture.