Identification of a follistatin-related protein from the tick Haemaphysalis longicornis and its effect on tick oviposition

The identification of ovary-associated molecules will lead to a better understanding of the physiology of tick reproduction and vector–pathogen interactions. A gene encoding a follistatin-related protein (FRP) was obtained by random sequencing from the ovary cDNA library of the tick Haemaphysalis longicornis. The full-length cDNA is 1157 bp, including an intact ORF encoding an expected protein with 289 amino acids. Three distinct domains were present in the deduced amino acids, namely, the follistatin-like domain, KAZAL, and two calcium-binding motifs, EFh. The sequence shows homology with the follistatin-related protein (FRP), which was thought to play some roles in the negative regulation of cellular growth. RT–PCR showed that the gene was expressed throughout the developing stages and mainly in the ovary as well as in fat body, hemocytes, salivary glands, and midgut. This gene was expressed in GST-fused recombinant protein with an expected size. The mouse antiserum against the recombinant protein recognized a 56-kDa native protein in both tick ovary and hemolymph. The recombinant proteins were found to have binding activity for both activin A and bone morphogenetic protein-2 (BMP-2). Silencing of FRP by RNAi showed a decrease in tick oviposition, which is consistent with the effect of a recombinant protein vaccine on the adult tick. These results showed that the tick FRP might be involved in tick oviposition. This is the first report of a member of follistatin family proteins in Chelicerata, which include ticks, spiders, and scorpions.