Teratocytes (TCs) are the cells derived from the embryonic serosal membrane of some parasitic hymenopteran insects. As a parasitic factor, TCs are multifunctional in host regulation by inducing nutritional, immune, and developmental alterations. However, little is understood about their genetic constituents. This study reveals a comprehensive view of the genes expressed by TCs through a transcriptome analysis based on RNAseq technology. More than 6.29 Gb sequences were used to assemble 34,686 contigs (>200 bp) and annotated into different functional categories. The TC transcriptome profile was clearly distinct from those of hemocytes and the fat body. The TC transcriptome contained components of insulin signaling and biosynthesis of juvenile hormone and 20-hydroxyecdysone. TCs also expressed various groups of digestive enzymes, supporting its nutritional role for the growing parasitoid larvae in parasitism. Furthermore, this transcriptome analysis annotated two kinds of immunosuppressive serine protease inhibitors (serpins) and Rho GTPase-activating proteins (RhoGAPs). To determine the biological functions of these factors, we devised ex vivo RNA interference (RNAi) by conducting knockdown of gene expression in in vitro cultured TCs followed by injection of the treated TCs to test insects. Ex vivo RNAi revealed that some serpins and RhoGAPs expressed in TCs inhibited host cellular immunity. This study reports a transcriptome of the unique TC animal cell, and its immunosuppressive genetic factors using ex vivo RNAi technology.

Cotesia plutellae has been known as a natural enemy against the Diamondback moth, Plutella xylostella via laying eggs into a larva. When the larva hatches from the egg, teratocytes also are released and expected to work as immune suppressor via secreting immune suppressive factors. In order to analyze the gene expression in teratocytes, total RNAs were isolated and genes expressed in the teratocyte were sequenced by Illumina HiSeq2000 RNASeq analysis. The information on RNA sequences was assembled by Trinity and contigs were annotated by Blast analysis. The levels of gene expression were calculated by FPKM. Approximately, 6.3 Gbs were obtained and 34,686 contigs were found and annotated. Forty two percent of contigs were homologous to previously reported genes and classified by gene ontologies: the highly abundant components are metabolic process, biological regulation and cellular process in biological function; binding, catalytic activity and transporter activity in molecular function; cell part, membrane part and organelle in cellular function, respectively. In addition, some teratocyte transcripts of C. plutellae are related to host regulation such as immunosuppression and nutrition: Ankyrin repeat proteins, Serpin, protease, lipase, chitinase and scavenger receptor.