Gene expression of the vitellogenins and the receptors during the annual reproductive cycle

Atlantic salmon belongs to the primitive group of protacanthomorph teleost and has two Vtg genes (VtgAsa and VtgAsb) and two VtgR genes (VtgR1 and VtgR2). The focus of our research was to characterize predicted salmon Vtgs and VtgRs by alignment analysis, and to evaluate annual changes in gene expression in four tissues (liver, brain, heart and ovary) during reproductive cycle by qPCR quantification procedure. The annual changes in gonad-somatic index and plasma estrogen concentration were also presented to establish the relationship with Vtgs and VtgRs during reproducing cycle. qPCR revealed that VtgAsa and VtgAsb were predominantly expressed in liver, while weak expression was detected in ovary, brain and heart of female fish. Vtg increased significantly during previtellogenesis, and kept on highest level in vitellogenesis period. VtgR genes were predominantly expressed in ovary but limited in extra-ovarian tissue, and VtgR2 was undetectable in liver tissue. Both VtgR1 and VtgR2 were expressed at highest levels in previtellogenetic, and then gradually decreased with the oocyte growth and E2 accumulation.M-A