In penaeid shrimp species, vitellogenin (VTG) synthesis in the ovary and hepatopancreas is under the inhibitory regulation of a neuroendocrine system, the X-organ/sinus gland complex in the paired eyestalks, and eyestalk ablation (removal of the X-organ/sinus gland complex) is widely used for inducing ovarian development. However, the difference in effects of bilateral and unilateral ablation on VTG gene expression has not been clarified so far. In the present study, VTG synthesis was monitored over a 16-day period after ablation and compared between replicates of immature female kuruma prawns, Marsupenaeus (Penaeus) japonicus, that had been bilaterally or unilaterally ablated and control specimens. After bilateral ablation, ovarian development was induced, and the ovarian weight, hemolymph VTG levels, and VTG mRNA levels in the ovary increased significantly. Significant VTG mRNA increase was detected 12 h after bilateral ablation. In contrast, after unilateral ablation, ovarian development was not induced, and the ovarian weight, hemolymph VTG levels, and VTG mRNA levels in the ovary did not change significantly from the control. These results indicate that in immature female prawns, unilateral ablation does not induce VTG gene expression, whereas bilateral ablation induces rapid VTG gene expression (<12 h). The ineffectiveness of unilateral ablation suggests that the remaining X-organ/sinus gland complex in the unilaterally ablated female prawns may secrete sufficient VIH to suppress VTG synthesis.
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