Identification of three genes in the methyl farnesoate signaling pathway from the Pacific whiteleg shrimp Litopenaeus vannamei and their roles in methyl farnesoate-mediated ovarian development

Methyl farnesoate (MF) is an essential regulator of development and reproduction in arthropods. This study identified the MF signaling response genes and analyzed their potential roles in ovarian development of the Pacific whiteleg shrimp Litopenaeus vannamei. Three critical genes, including Methoprene-tolerant (LvMet), Retinoid X receptor (LvRXR) and Krüppel homolog 1 (LvKr-h1), were identified from L. vannamei. Their expression increased and reached the peak at the ovarian mature stage. In vitro experiments revealed that LvMet, LvRXR, LvKr-h1, and vitellogenin genes (LvVg1 and LvVg2) in the hepatopancreas explants were significantly induced by MF, while LvMet and LvKr-h1 mRNA were significantly induced in the ovarian explants. In vivo injection of MF significantly stimulated LvMet expression in the ovaries, and induced the expression of LvRXR and LvKr-h1 in the hepatopancreas and ovaries. When either LvMet or LvRXR was silenced, LvKr-h1 expression was significantly decreased in the hepatopancreas. Silencing LvKr-h1 expression also significantly decreased LvMet and LvRXR expression. Yeast two-hybrid experiment further proved that LvMet weakly interacted with LvRXR. In conclusion, LvMet, LvRXR and LvKr-h1 constitute crucial components of the MF signaling pathway regulating ovarian development of L. vannamei, and LvMet forms a heterodimer with LvRXR in response to MF to activate the transcription of LvKr-h1.