Functional characterization of recombinant gonad-inhibiting hormone (GIH) and implication of antibody neutralization on induction of ovarian maturation in marine shrimp

Ovarian maturation in crustacean is controlled by an eyestalk neuropeptide called gonad-inhibiting hormone (GIH) that is presumed to inhibit vitellogenin synthesis. In this study, a recombinant protein of GIH of Penaeus monodon (rPem-GIH) was expressed in Pichia pastoris expression system and purified to homogeneity by reversed-phase SPE (C₁₈). The purified rPem-GIH significantly reduced vitellogenin mRNA level in primary tissue culture derived from previtellogenic ovary of P. monodon broodstock by 45.7% compared with the untreated group. This effect was similar to that of partially purified optic lobe extract, and demonstrated that the rPem-GIH possessed gonad-inhibiting activity. A monoclonal antibody specific to Pem-GIH (anti-GIH mAb) was able to neutralize the activity of GIH from the partially purified optic lobe extract to about 58% by in vitro assay in primary tissue culture of the ovary. Peptide mapping revealed that amino acids 16 to 20 (MYNKV) of the mature Pem-GIH may serve as an epitope of anti-GIH mAb. A single injection of anti-GIH mAb into wild previtellogenic P. monodon was able to induce ovarian maturation and spawning at a comparable rate to the eyestalk ablation. Our results demonstrate neutralization effect of anti-GIH mAb on vitellogenesis inhibitory action of GIH, and thus provide a potential alternative to induce ovarian maturation in P. monodon broodstock.